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Cytokines and regulation of allergic sensitization to chemicals
ELSEVIER
Toxicology 93 (1994) I - 11
Review article
Cytokines and regulation of allergic sensitization to chemicals * Ian Kimber Zeneca Central Toxicology Laboratory. Alderley Park, Uacclesfield, Cheshire, SK10 4TJ, UK
Received 3 October 1993; accepted 22 November
1993
Abstract Sensitization to chemicals and the elicitation of allergic reactions results from the stimulation of specific immune responses. Adaptive immunity is orchestrated by cytokines, a family of inducible glycoproteins that influence in many ways the behaviour of, and interaction between, cells which mediate immune and inflammatory responses. In this article the role of cytokines in the development of cutaneous immune responses to chemical allergens and in directing the quality of immune responses provoked by such materials is discussed.
Keywords: Cytokines; Chemical allergy; Dendritic cells; T lymphocytes
1. Introduction Allergy results from the exposure of susceptible individuals to sensitizing chemicals and is dependent upon the induction of specific immune responses. The nature of immune responses provoked by chemical allergens is essentially no different from that which characterizes protective immunity and provides host resistance against infectious disease. The immune system comprises a systemic network of tissues, cells *Presented
at the Second
1993. Elsevier Science Ireland Ltd. SSDI 0300-483X(94)02879-Y
Summer
School
in Immunotoxicology,
Beaune, France, 13-15 October
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I. Kimber/Toxicology 93 (1994) 1-11
and molecules which must act in concert, and in an ordered fashion, to initiate and sustain adaptive immune responses. It is now apparent that normal immune function is orchestrated by cytokines; a diverse family of inducible glycoproteins, produced by various cell types, which mediate local interaction and distant communication between cellular elements of immune and inflammatory responses. Cytokines may act directly as inducers and regulators of cell growth, division and differentiation, as stimulators of cell movement and directed migration and as controllers of cell function and cellular interaction via induced changes in the expression of membrane determinants such as major histocompatibility complex antigens, adhesion molecules and receptors for cytokines themselves. The biology of cytokines is complex. They may act in endocrine, paracrine or autocrine fashion and may exhibit complementary, synergistic or antagonistic effects. The purpose of this article is to examine the role of cytokines in two aspects of the immune response to chemical allergens: (i) the role of epidermal cytokines and Langerhans cells during the induction phase of sensitization to chemicals encountered in the skin and (ii) the influence of T lymphocyte cytokines on the characteristics of immune responses to chemical allergens.
2. Epidermal cytokines, Langerhans cells and skin sensitization Langerhans cells (LCs) are members of the family of dendritic cells (DCs) - - bone marrow-derived cells characterized by possession of dendrites and a large surface area:volume ratio - - which are found in small numbers in lymphoid organs and in those tissues that come into closest apposition with the external environment (Steinman, 1991). LCs form a contiguous network in the epidermis where they are considered to serve as a trap for exogenous skin antigens (Shelley and Juhlin, 1976). Following topical exposure to skin sensitizing chemicals, DCs accumulate in the lymph nodes draining the site of contact. Many of the DCs which arrive in the nodes bear high levels of the inducing allergen. Indeed, during the first 24 h following skin sensitization all the cell-bound allergen found within draining nodes appears to be associated with DCs (Knight et al., 1985; Macatonia et ai., 1986, 1987; Kinnaird et al., 1989; Cumberbatch and Kimber, 1990; Kimber and Cumberbatch, 1992). The DCs which arrive in the lymph nodes derive from LCs which, in response to local sensitization, migrate from the skin and travel to the nodes via afferent lymphatics (Macatonia et al., 1987; Munn et al., 1989; Kripke et al., 1990; Kimbe'r and Cumberbatch, 1992). This process of LC movement and antigen transport is thought to be of central importance for the effective induction of skin sensitization. An interesting feature is that LCs resident within the epidermis are comparatively inefficient antigen presenting cells (Schuler and Steinman, 1985). However, following receipt of the stimulus to migrate and by the time of arrival in the draining nodes, LCs have acquired the characteristics of lymphoid DCs and are able efficiently to stimulate T cell activation. Thus, the antigen-bearing DCs found within local lymph nodes following skin sensitization are effective antigen presenting cells both in vitro (Knight et al., 1985; Macatonia et al., 1986; Jones et al., 1989; Robinson, 1989) and in vivo (Knight et al., 1985; Kinnaird et al., 1989; Macatonia and Knight, 1989).
1. Kimber / ToxiCOlogy:93 (1994J 1- I 1
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Moreover, unlike epidermal LCs, the antigen-bearing DCs within draining nodes form stable clusters with T lymphocytes (Cumberbatch et al., 1991a). Langerhans cells in the skin are able to interact with and process foreign antigen (Streilein and Grammer, 1989). While in transit to the lymph nodes, however, this property is exchanged for immunostimulatory potential. The functional maturation of LCs into active antigen presenting cells is associated with and facilitated by an increased expression of several membrane determinants required for interaction with, and presentation of antigen to, T lymphocytes including major histocompatibility complex MHC class II (Ia) gene products (Cumberbatch et al., 1991b), intercellular adhesion molecule-1 (ICAM-1) (Cumberbatch et al., 1992) and the costimulatory molecule B7/BB1, a ligand for CD28 (Larsen et al., 1992). These events mirror in large part the changes to which LCs are subject during culture (Schuler and Steinman, 1985; Shimada et al., 1987; Witmer-Pack et al., 1987; Tang and Udey, 1991) and, by analogy with such in vitro studies, it is likely that granulocyte/macrophage colony-stimulating factor (GM-CSF), interleukin 1 (IL-1) and possibly other cytokines effect the functional maturation of LCs in vivo (WitmerPack et al., 1987; Heufler et al., 1988; Picut et al., 1988). The epidermis is a rich source of cytokines. In addition to GM-CSF and IL-1, epidermal cells (keratinocytes and Langerhans cells) produce, or can be stimulated to produce, a variety of cytokines including interleukins 6, 7, 8 and 10 (IL-6, IL-7, IL-8 and IL-10), macrophage inflammatory proteins lot and 2 (MIP-Ioc and MIP-2), tumour necrosis factor ot (TNF-Ot), transforming growth factors ot and/~ (TGF-Ot and TGF-/3) and interferon (IFN)-induced protein 10 (IP-10) (Barker, 1992; Enk and Katz, 1992a, b; Heufler et al., 1992). It is probable that epidermal cytokines are responsible not only for effecting the functional maturation of LCs during migration, but also for providing the stimulus for migration itself. Recent studies have demonstrated that TNF-Ot may represent an important stimulus for the movement of LCs from the epidermis following skin sensitization (Cumberbatch and Kimber, 1992; Cumberbatch et al., 1994). Consistent with the local availability ofcytokines being a requirement for the migration and maturation of LCs during skin sensitization is evidence that topical exposure of mice to contact allergens results in upregulation of epidermal mRNA for interleukin 1/3 (IL-1/~), IL-10, TNF-ot, GM-CSF and IP-10 (Enk and Katz, 1992a, b). The following sequence of events is therefore proposed to occur following skin contact with a chemical allergen. The sensitizing agent, either directly or indirectly, stimulates the increased synthesis and secretion of certain epidermal cytokines, including those known or suspected to influence LC behaviour. Tumour necrosis factor ot provides one signal for LC migration. Subsequently, GM-CSF and possibly other cytokines induce a functional and phenotypic maturation of LCs in transit to the lymph nodes such as to permit effective antigen presentation and the initiation of T lymphocyte responses. Langerhans cells and DCs were considered originally not to produce cytokines. It is of some interest, therefore, that recent investigations have shown LCs to be the major or exclusive source within the epidermis of IL-I~ (Enk and Katz, 1992a; Heufler et al., 1992; Matsue et al., 1992; Schreiber et al., 1992) and MIP-lot (Heufler et al., 1992; Matsue et al., 1992). Furthermore, there is evidence that the expression
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L Kimber / Toxicology 93 (1994) 1-11
Table 1 Epidermal cytokine expression by murine Langerhans cells Cytokine
Selective expression by LCs
Expression by keratinocytes
Modulationduring culture of LCs
Interleukin i/3 (IL-I/3) Macrophage inflammatoryprotein l a
+ +
-
Increased Decreased
-
+
Decreased
-
+
Increased
(MIP-i~)
Macrophage inflammatoryprotein 2 (MIP-2) Interleukin 6 (IL-6)
Data from Enk and Katz (1992a), Heufler et al. (1992), Matsue et al. (1992) and Schreiber et al. (1992).
of cytokines by LCs is modulated differentially during culture, a process which can be considered equivalent to the functional maturation of these cells in vivo. Expression of IL-1/3 is upregulated strongly following culture of LCs, while m R N A for MIP-lc~ (and MIP-2) is decreased (Heufler et al., 1992). In addition, cultured LCs produce IL-6 (Heufler et al., 1992; Schreiber et al., 1992) (Table 1). With regard to the acquisition by LCs of immunostimulatory and antigen presenting potential it may be relevant that culture is associated with an increased expression of two cytokines (IL-1/3 and IL-6) which are known to act as important costimulatory molecules for T lymphocyte activation. The significance of LC-derived MIP-Ic~ and the downregulation of this cytokine during culture is uncertain, although it has been suggested that this molecule serves as a paracrine regulator of keratinocyte stem cell development in the skin (Heufler et al., 1992). The expression of certain epidermal cytokines is increased in response to various types of cutaneous stimuli. Thus, for example, it is known that skin sensitizers, skin irritants and local irradiation with ultraviolet (UV) light all induce the increased production of epidermal TNF-c~ (Kock et al., 1990; Enk and Katz, 1992a). It has been demonstrated, however, that the upregulation of some epidermal cytokines is provoked selectively by chemical allergens. Enk and Katz (1992a, b) have shown that topical exposure of mice to chemical allergens such as dinitrofluorobenzene
Table 2 Selective upregulation of certain epidermal cytokines by chemical allergens Cytokine Interleukin 1/3 (IL-I/3) lnterleukin 10 (IL-10) Interferon-induced protein 10 (IP-10) Macrophage inflammatoryprotein 2 (MIP-2)
Source Langerhans cells
Keratinocytes
--
+
--
+
+
+
Taken from Enk and Katz (1992a, b) and Heufler et al. (1992).
L Kirnber / Toxicology 93 (1994) 1-11
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(DNFB), but not to skin irritants, induces increased epidermal cell mRNA for IL-1/3, IL-10, MIP-2 and IP-10 (Table 2). Interleukin 1/3 is of particular interest. This cytokine is expressed solely by LCs within the epidermis and production is increased in situ by chemical allergens and also during the maturation of LCs into immunostimulatory DCs. It has been found recently that intradermal injection of mice with IL-1/~causes a rapid and significant increase in epidermal mRNA for a number of cytokines including TNF-a (Enk et al., 1993). Moreover, skin sensitization was shown to be inhibited if the availability of local IL-1/~was reduced (Enk et al., 1993). On the basis of these data it may be that an early and essential event during the induction phase of contact sensitization is the stimulation of IL-I~ production by LCs which in turn induces the release of keratinocyte-derived cytokines necessary for LC migration and maturation. Although uncertainties remain, the importance of epidermal cytokines for the initiation of cutaneous immune responses is beyond doubt. Further work should provide a detailed picture of the molecular interactions which are induced in the skin by chemical allergens and which result in the development of contact sensitization.
3. T helper cells, cytokines and allergic responses Some chemical sensitizers are able to cause occupational respiratory allergy, while others are contact allergens but fail to induce pulmonary hypersensitivity. The type of sensitization caused by chemicals, and the form allergic reactions will take following subsequent re-exposure of a sensitized individual, is to a large extent governed by the quality of immune responses induced. Immune effector mechanisms can be divided broadly into cell-mediated and humoral (antibody-mediated) reactions. Both play important roles in allergic responses. Contact hypersensitivity, one form of delayed-type hypersensitivity reaction, is effected by a cell-mediated immune response in which T lymphocytes play a central role. In contrast, immediate-type hypersensitivity reactions, such as those that characterize the acute onset of respiratory allergy, are provoked by antibody, and in particular by antibody of the IgE class. In considering the relationship between cell-mediated and humoral processes in the development of immune responses the activity of T helper cells and the cytokines they elaborate are of particular relevance. T helper (Th) cells, defined by possession of the membrane determinant CD4, promote immune responses and cooperate with B lymphocytes in the generation of antibody responses. In 1986 it was demonstrated that in mice there exists a functional heterogeneity among CD4 ÷ Th cells. Two main classes were recognized and designated Thl and Th2 (Mosmann et al., 1986). These populations differ with respect to their cytokine products. In mice both populations produce interleukin 3 (IL-3) and GM-CSF. However, only Thl cells secrete interleukin 2 (IL-2), interferon 3' (IFN-3') and tumour necrosis factor/3 (TNF-/3; lymphotoxin) and only Th2 cells produce interleukins 4, 5, 6 and 10 (IL-4, IL-5, IL-6 and IL-10) (Mosmann and Coffman, 1989; Mosmann et al., 1991) (Table 3). A similar, but not identical, heterogeneity among human Th cells has now been described also (Romagnani, 1991). The relevance of Th cell subpopulations to the development of allergic disease is that their soluble products exert opposing regula-
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L Kirnber/Toxicology 93 (1994) 1-11
Table 3 Cytokine secretion by murine Th I and Th2 cells Cytokine
Thl cells
Th2 cells
Interleukin 3 (IL-3) Granulocyte/macrophagecolony-stimulatingfactor (GM-CSF) Interferon-3,(IFN-3,) lnterleukin 2 (IL-2) Tumour necrosis factor B (TNF-#; lymphotoxin) Interleukin 4 (IL-4) lnterleukin 5 (1L-5) lnterleukin 6 (IL-6) interleukin 10 (IL-10)
+ +
+ +
+ + + -
+ + + +
Taken from Mosmann et al. (1991).
tory effects on IgE production and on other aspects of allergic processes. The induction of IgE responses in mice is dependent upon IL-4 (Finkelman et al., 1988a). Mice homozygous for a mutation that inactivates the gene for IL-4 lack detectable IgE and fail to mount IgE responses (Kuhn et al., 1991), while mice which possess a transgene for the cytokine and constitutively produce high levels of IL-4 exhibit increased concentrations of serum IgE (Tepper et al., 1990; Burstein et al., 1991). In contrast, IFN-3,, a product of Thl cells, antagonizes the production of IgE antibody (Finkelman et al., 1988b). In man, also, these cytokines regulate reciprocally the synthesis of IgE (Del Prete et al., 1988; Pene et al., 1988). The initiation of IgE responses and the development of immediate-type hypersensitivity will be favoured, therefore, by allergens, or conditions of exposure to allergens, which result in a preferential stimulation of Th2-type responses. The selective activation of Th 1 cells will not normally be permissive for IgE production. Th ltype immune responses are, however, compatible with the induction by chemical allergens of contact sensitization. It has been found that delayed-type hypersensitivity responses are effected by Thl cells. (Cher and Mosmann, 1987), and that IFN-3, plays an important role in this process (Diamanstein et al., 1988; Fong and Mosmann, 1989). Consistent with the stimulation of preferential Th cell activation by contact and respiratory sensitizers are the characteristics of immune responses provoked in mice by chemical allergens. Topical exposure of mice to respiratory chemical allergens, such as trimellitic anhydride and phthalic anhydride, results in strong IgE responses. In contrast, under the same conditions of exposure, contact allergens known or suspected not to cause respiratory hypersensitivity (such as dinitrochlorobenzene and oxazolone) fail to elicit an IgE response but do provoke comparatively high levels of IgG2a antibody, an isotype known to be stimulated by IFN-3, (Dearman and Kimber, 1991, 1992; Dearman et al., 1992). It can be suggested therefore that the physico-chemical properties of the allergen itself, or the way in which it is handled, processed and presented will determine the characteristics of the immune response induced and the type of allergic reaction that will be provoked following subsequent challenge.
I. Kimber / Toxicology 93 (1994) 1-11
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Cytokines appear also to play an important role in the initial generation of divergent Th cell subpopulations themselves. Th cells displaying a phenotype of selective cytokine synthesis develop as the immune system matures. It has been shown that IL-4 favours the development of Th2 cells, while IFN-~, promotes Thl cells (Coffman et al., 1991; Abehsira-Amar et al., 1992; Gross et al., 1993; Kopf et al., 1993). Cellular vectors of the natural immune system, mast cells and natural killer (NK) cells, may be the source of these cytokines (IL-4 and IFN-~, respectively) during the early stages of an adaptive immune response prior to the appearanCe of differentiated Thl and Th2 cells (Romagnani, 1992). Other cytokines, such as IL-12 (IL-12) (Trinchieri, 1993) and IL-10 (Hsieh et al., 1992) may also be promotors, respectively, of Thl and Th2 cell development. In addition to regulating the production of IgE antibody and controlling the development of Th subpopulations, the soluble products of Th I and Th2 cells influence in other ways the allergic response. Interleukins 3, 4 and 10 are all mast cell growth factors or cofactors (Smith and Rennick, 1986; Thomson-Snipes et al., 1991) and I L5 is a growth and differentiation factor for eosinophils (Yokota et al., 1987). Moreover, IL-4 will enhance the secretory potential of mast cells in vitro (Coleman et al., 1992, 1993). Here again IFN-~, has a reciprocal effect and serves to reduce serotonin release by mast cells activated in culture (Coleman et al., 1991, 1992, 1993). The severity of local allergic reactions may be influenced in other ways by cytokines. Interleukin 5 controls the accumulation of eosinophils at the site of allergen-induced respiratory reactions (Chand et al., 1992; Gulbenkian et al., 1992; Iwami et al., 1992, 1993), a process antagonized by IFN-~ (Iwamoto et al., 1993). In addition, IL-4 has been shown to depress dermal contact hypersensitivity reactions (Gautam et ai., 1992). Divergent Th cell responses also characterize human allergic disease. Clones of T lymphocytes derived from the peripheral blood of nickel sensitive donors secrete IFN-~,, but only low or undetectable levels of Th2 cytokines (Kapsenberg et al., 1991, 1992). In contrast, T cell clones specific for aeroallergens which induce in man IgE-mediated hypersensitivity reactions have been shown to produce Th2 cytokines but not IFN-~, (Parronchi et al., 1991). Also, CD4 ÷ T cell clones prepared from lesional skin biopsies of house dust mite-allergic atopic donors were found to be of Th2 phenotype on the basis of cytokine production (van der Heijden et al., 1991). A predominance of Th2-type cells in the sites of cutaneous reactions in atopic individuals has been demonstrated also by in situ hybridization. Cells infiltrating lesional skin expressed mRNA for IL-3, IL-4, IL-5 and GM-CSF, but not for IFN-~, (Kay et al., 1991). Finally, it should be emphasized that other cytokines may also influence IgE antibody responses. It has been suggested that interleukin 9 (IL-9) may potentiate IL-4-induced IgE synthesis (Petit-Frere et al., 1993) and that a recently characterized product of T lymphocytes, interleukin 13 (IL-13), is able to induce an IL-4independent synthesis of IgE by human B lymphocytes (Punnonen et al., 1993). The available data indicate therefore that cytokines, and more particularly the relative availability of cytokines, influence not only the development of allergic responses but also the hypersensitivity reactions that are provoked by exposure to
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1. Kimber/Toxicology 93 (1994) 1-11
allergen in sensitized individuals. The induction of Th2-type responses will promote immediate type hypersensitivity. The products of activated Th2 cells stimulate IgE production, serve as growth factors for mast cells and eosinophils and as potentiators of mast cell function, promote the accumulation of eosinophils at inflammatory sites and will encourage the further development of Th2 cells themselves. In contrast, preferential Th 1-type responses will favour cell-mediated immunity and the development of contact hypersensitivity. Interferon-7 produced by Thl cells antagonizes IgE responses, downregulates mast cell function and inhibits other aspects of immediate type hypersensitivity reactions. Moreover, IFN-7 stimulates the generation of Thl cells. Other cytokines, and other regulatory cells and molecules, influence the initiation of IgE responses and allergic processes. It is apparent, however, that the products of differentiated Th cells play a central, and probably decisive, role in determining the characteristics of immune responses that will be provoked by exposure to chemical allergens. References Abehsira-Amar, O., Gibert, M., Joliy, M., Theze, J. and Jankovic, D.L. (1992) IL-4 plays a dominant role in the differential development of Tho into Thl and Th2 cells. J. Immunol. 148, 3820-3829. Barker, J.N.W.N. (1992) Role of keratinocytes in allergic contact dermatitis. Contact Derm. 26, 145-148. Burstein, H.J., Tepper, R.I., Leder, P. and Abbas, A.K. (1991) Humoral immune functions in IL-4 transgenic mice. J. Immunol. 147, 2950-2956. Chand, N., Harrison, J.E., Rooney, S., Pillar, J., Jakubicki, R., Nolan, K. Diamantis W. and Sofia, R.D. (1992) Anti-IL-5 monoclonal antibody inhibits allergic late phase bronchial eosinophilia in guinea pigs: a therapeutic approach. Eur. J. Pharmacol. 211, 121-124. Cher, D.J. and Mosmann, T.R. (1987) Two types of murine helper T cell clone. 1I. Delayed type hypersensitivity is mediated by Thl clones. J. Immunol. 138, 3688-3694. Coffman, R.L., Varkila, K., Scott, P. and Chatelain, R. (1991) Role of cytokines in the differentiation of CD4+ T-cell subsets in vivo. Immunol. Rev. 123, 189-207. Coleman, J.W., Buckley, M.G., Holliday, M.R. and Morris, A.G. (1991) Interferon-y inhibits serotonin release from mouse peritoneal mast cells. Eur. J. Immunol. 21, 2559. Coleman, J.W., Holliday, M.R. and Buckley, M.G. (1992) Regulation of the secretory function of mouse peritoneal mast cells by IL-3, IL-4 and IFN-% int. Arch. Allergy Immunol. 99, 408-410. Coleman, J.W., Holliday, M.R., Kimber, I., Zsebo, K.M. and Galli, S.J. (1993) Regulation of mouse peritoneal mast cell secretory function by stem cell factor, IL-3 or IL-4. J. Immunol. 150, 556-562. Cumberbatch, M. and Kimber, 1. (1990) Phenotypic characteristics of antigen bearing cells in the draining lymph nodes of contact sensitized mice. Immunology 71,404-410. Cumberbatch, M. and Kimber, I. (1992) Dermal tumonr necrosis factor-a induces dendritic cell migration to draining lymph nodes, and possibly provides one stimulus for Langerhans cell migration. Immunology 75, 257-263. Cumberbatch, M., lllingworth, I. and Kimber, I. (1991a) Antigen-bearing dendritic cells in the draining lymph nodes of contact sensitized mice. Cluster formation with lymphocytes. Immunology 74, 139-145. Cumberbatch, M., Gould, S.J. Peters, S.W. and Kimber, 1. (1991b) MHC class II expression by Langerhans cells and lymph node dendritic cells: possible evidence for maturation of Langerhans cells following contact sensitization. Immunology 74, 414-419. Cumberbatch, M., Peters, S.W., Gould, S.J. and Kimber, 1. (1992) Intercellular adhesion molecule-I (ICAM-1) expression by lymph node dendritic cells. Comparison with epidermal Langerhans cells. lmmunol. Lett. 32, 105-110.
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Cumberbatch, M., Fielding, I. and Kimber, I. (1994) Modulation of epidermal Langerhans cell frequency by tumour necrosis factor c~ (TNF-ct). Immunology 81, 395-401. Dearman, R.J. and Kimber, I. (1991) Differential stimulation of immune function by respiratory and contact chemical allergens. Immunology 72, 563-570. Dearman, R.J. and Kimber, I. (1992) Divergent immune responses to respiratory and contact chemical allergens: antibody elicited by phthalic anhydride and oxazolone. Clin. Exp. Allergy 22, 241-250. Dearman, R.J., Basketter, D.A., Coleman, J.W. and Kimber, 1. (1992) The cellular and molecular basis for divergent allergic responses to chemicals. Chem.-Biol. Interact. 84, 1-10. Del Prete, G., Maggi, E., Parronchi, P., Chretien, 1., Tiri, D., Macchia, M., Ricci, J., Banchereau, J., De Vries, J. and Romagnani, S. (1988) 1L-4 is an essential factor for the IgE synthesis induced in vitro by human T cell clones and their supernatants. J. Immunol. 140, 4193-4198. Diamanstein, T., Eckert, R., Volk, H-D. and Kupier-Weglinski, J-W. (1988) Reversal by interferon-'y of inhibition of delayed-type hypersensitivity induction by anti-CD4 or anti-interleukin 2 receptor (CD25) monoclonal antibodies. Evidence for the physiological role of CD4+ Thl+ subset in mice. Eur. J. Immunol. 18, 2101-2103. Enk, A.H. and Katz, S.I. (1992a) Early molecular events in the induction phase of contact sensitivity. Proc. Natl. Acad. Sci, USA 89, 1398-1402. Enk, A.H. and Katz, S.I. (1992b) Identification and induction of keratinocyte derived IL-10. J. lmmunol. 149, 92-95. Enk, A.H., Angeloni, V.L., Udey, M.C. and Katz, S.I. (1993) An essential role for Langerhans cellderived IL-I/~ in the initiation of primary immune responses in the skin. J. lmmunol. 150, 3698-3704. Finkelman, F.D., Katona, I.M., Urban Jr. J,F., Holmes, J., Ohara, J. Tung, A.S., Sample, J.G. and Paul, W.E. (1988a) IL-4 is required to generate and sustain in vivo lgE responses. J. lmmunol. 144, 2335-2341. Finkelman, F.D., Katona, I.M., Mosmann, T.R. and Coffman, R.L. (1988b) I FN-3, regulates the isotypes of lg secreted during in vivo humoral immune responses. J. lmmunol. 140, 1022-1027. Fong, T.A.T. and Mosmann, T.R. (1989) The role of IFN-'t in delayed-type hypersensitivity mediated by Thl clones. J. Immunol. 143, 2887-2893. Gautam, S.C., Chikkala, N.F. and Hamilton, T.A. (1992) Anti-inflammatory action of 1L-4. Negative regulation of contact sensitivity to trinitrochlorobenzene. J., Immunol. 148, 1411-1415. Gross, A., Ben-Sasson, S.Z. and Paul, W.E. (1993) Anti-IL-4 diminishes in vivo priming for antigenspecific IL-4 production by T cells. J. Immunol. 150, 2112-2120. Gulbenkian, A.R., Egan, R.W., Fernandes, X., Jones, H., Kreutner, W. Kung, T., Payvandi, F., Sullivan, L., Zurcher, J.A. and Watnik, A.S. (1992) Interleukin-5 modulates eosinophil accumulation in allergic guinea pig lung. Am. Rev. Respir. Dis. 146, 263-268. Heufler, C. Koch, F. and Schuler, G. (1988) Granulocyte/macrophage colony stimulating factor and interleukin 1 mediate the maturation of murine epidermal Langerhans cells into potent immunostimulatory dendritic cells. J. Exp. Med. 167, 700-705. Heufler, C., Topar, G., Koch, F., Trockenbacher, B., Kampgen, E. Romani, N. and Schuler, G. (1992) Cytokine gene expression in murine epidermal cell suspensions: interleukin 1/3 and macrophage inflammatory protein lc~ are selectively expressed in Langerhans cells but are differentially regulated in culture. J. Exp. Med. 176, 1221-1226. Hsieh, C-S., Heimberger, A.B., Gold, J.S., O'Garra, A. and Murphy, K.M. (1992) Differential regulation of T helper phenotype development by interleukin 4 and 10 in an c~ T-cell-receptor transgenic system. Proc. Natl. Acad. Sci. USA 89, 6065-6069. lwami, T., Nagai, H., Suda, H., Tsuruoka, N. and Koda, A. (1992) Effect of murine recombinant interleukin-5 on the cell population in the guinea-pig airways. Br. J. Pharmaco|. 195, 19-22. Iwami, T., Nagai, H., Tsuruoka, N. and Koda, A. (1993) Effect of murine recombinant interleukin-5 on bronchial reactivity in guinea pigs. Clin. Exp. Allergy 23, 32-38. Iwamoto, I., Nakajima, H., Endo, H. and Yoshida, S. (1993) Interferon -/ regulates antigen-induced eosinophil recruitment into the mouse airways by inhibiting the infiltration of CD4+ T cells. J. Exp. Med. 177, 573-576. Jones, D.A., Morris, A.G. and Kimber, !. (1989) Assessment of the functional activity of antigen-bearing
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dendritic cells isolated from the lymph nodes of contact-sensitized mice. Int. Arch. Allergy Appl. lmmunol. 90, 230-236. Kapsenberg, M.L., Wierenga, E.A., Bos, J.D. and Jansen, H.M. (1991) Functional subsets of allergenreactive human CD4 ÷ T cells. Immunol. Today 12, 392-395. Kapsenberg, M.L., Wierenga, E.A., Stiekma, F.C.M., Tiggelman, A.M.B.C. and Bos, J.D. (1992) Thl lymphokine production profiles of nickel-specific CD4+ T lymphocyte clones from nickel contact allergic and non-allergic individuals. J. Invest. Derm. 98, 59-63. Kay, A.B., Ying, S., Varney, V., Gaga, M., Durham, S.R., Moqbel, R. Wardlaw, A.J. and Hamid, Q (1991) Messenger RNA expression of the cytokine gene cluster, interleukin 3 (IL-3), IL-4, IL-5 and granulocyte/macrophage colony stimulating factor, in allergen-induced late phase cutaneous reactions in atopic subjects. J. Exp. Med. 173, 775-778. Kimber, I. and Cumberbatch, M. (1992) Dendritic cells and cutaneous immune responses to chemical allergens. Toxicol. Appl. Pharmacol. 117, 137-146. Kinnaird, A., Peters, S.W., Foster, J.R. and Kimber, I. (1989) Dendritic cell accumulation in the draining lymph nodes during the induction phase of contact allergy in mice. Int. Arch. Allergy Appl. Immunol. 89, 202-210. Knight, S.C., Krejci, J., Malkovsky, M., Colizzi, V., Gautam, A. and Asherson, G.L. (1985) The role of dendritic cells in the initiation of immune responses to contact sensitizers. I. In vivo exposure to antigen. Cell. lmmunol. 94, 427-434. Kock, A., Schwarz, T., Kirnbauer, R., Urbanski, A., Perry, P. Ansel, J.C. and Luger, T.A. (1990) Human keratinocytes are a source for tumour necrosis factor tx: evidence for synthesis and release upon stimulation with endotoxin or ultraviolet light. J. Exp. Med. 172, 1609-1614. Kopf, M., Le Gros, G., Bachmann, M., Lamers, M.C., Bluethmann, H. and Kohler, G. (1993) Disruption of the murine IL-4 gene blocks Th2 cytokine synthesis. Nature 362, 245-248. Kripke, M.L., Munn, C.G., Jeevan, A., Tang, J-M. and Bucana, C. (1990) Evidence that cutaneous antigen-presenting cells migrate to regional lymph nodes during contact sensitization. J. lmmunol. 145, 2833-2838. Kuhn, R., Rajewsky, K. and Muller, W. (1991) Generation and analysis of interleukin-4 deficient mice. Science 254, 707-710. Larsen, C,P., Ritchie, S.C., Pearson, T.C., Linsley, P.S. and Lowry, R.P. (1992) Functional expression of the costimulatory molecule, B7/BBI, on murine dendritic cell populations. J. Exp. Med. 176, 1215-1220. Macatonia, S.E. and Knight, S.C. (1989) Dendritic cells and T cells transfer sensitization for delayed-type hypersensitivity after skin painting with contact sensitizer. Immunology 66, 96-99. Macatonia, S.E., Edwards, A.J. and Knight, S.C. (1986) Dendritic cells and the initiation of contact sensitivity to fluorescein isothiocyanate. Immunology 59, 509-514. Macatonia, S.E., Knight, S.C., Edwards, A.J., Griffiths, S. and Fryer, P. (1987) Localization of antigen on lymph node dendritic cells after exposure to the contact sensitizer fluorescein isothiocyanate. Functional and morphological studies. J. Exp. Med. 166, 1654-1667. Matsue, H., Cruz Jr. P.D., Bergstresser, P.R. and Takashima, A. (1992) Langerhans cells are the major source ofmRNA for IL-IB and MIP-la among unstimulated mouse epidermal cells. J. Invest. Derm. 99, 537-541. Mosmann, T.R. and Coffman, R.L. (1989) Heterogeneity of cytokine secretion patterns and functions of helper T cells. Adv. lmmunol. 46, 111-147. Mosmann, T.R., Cherwinski, H., Bond, M.W., Giedlin, M.A. and Coffman, R.L. (1986) Two types of murine helper T cell clone. I. Definition according to profiles of lymphokine activities and secreted proteins. J. immunol. 136, 2348-2357. Mosmann, T.R., Schumacher, J.H., Street, N.F., Budd, R., O'Garra, A. Fong, T.A.T., Bond, M.W. Moore, K.W.M., Sher, A. and Fiorentino, D.F. (1991) Diversity of cytokine synthesis and function of mouse CD4+ T cells. Immunol. Rev. 123, 209-229. Munn, C.G. Bucana, C. and Kripke, M.L. (1989) Antigen-binding cells from lymph nodes of mice sensitized epicutaneously with hapten have features of epidermal Langerhans cells. J. Invest. Derm. 92, 487. Parronchi, P., Macchia, D., Piccinni, M-P., Biswas, P., Simonelli, C. Maggi, E., Ricci, M., Ansari, A.A.
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11
and Romagnani, S. (1991) Allergen and bacterial antigen-specific T-cell clones established from atopic donors show a different profile of cytokine production. Proc. Natl. Acad. Sci. USA 88, 4538-4542. Pene, J., Rousset, F., Briere, F., Chretien, 1., Paliard, X., Banchereau, J. Spits, H. and De Vries, J.E. (1988) IgE production by normal human B cells induced by alloreactive T cell clones is mediated by IL-4 and suppressed by 1FN~. J. lmmunol. 141, 1218-1224. Petit-Frere, C., Dugas, B., Braquet, P. and Mencia-Huerta, J.M. (1993) lnterleukin-9 potentiates the interleukin-4-induced IgE and lgGl release from murine B lymphocytes. Immunology 79, 146-151. Picut, C.A., Lee, C.S., Dougherty, E.P., Anderson, K.L. and Lewis, R.M. (1988) lmmunostimulatory capabilities of highly enriched Langerhans cells in vitro. J. Invest. Derm. 90, 201-206. Punnonen, J., Aversa, G., Cocks, B.G., McKenzie, A.N.J., Menon, S. De Waal Malefyt, R. and De Vries, J.E. (1993) Interleukin 13 induces interleukin 4-independent IgG4 and IgE synthesis and CD23 expression by human B cells. Proc. Natl. Acad. Sci. USA 90, 3730-3734. Robinson, M.K. (1989) Optimization of an in vitro lymphocyte blastogenesis assay for predictive assessment of immunologic responsiveness to contact sensitizers. J. Invest. Derm. 92, 860-867. Romagnani, S. (1991) Human THI and TH2 subsets: doubt no more. lmmunol. Today 12, 256-257. Romagnani, S. (1992) Induction of THI and TH2 responses: a key role for the "natural' immune responses. Immunol. Today 13, 379-381. Schreiber, S., Kilgus, O., Payer, E., Kutil, R., Elbe, A., Mueller, C. and Stingl, G. (1992) Cytokine pattern of Langerhans cells isolated from murine epidermal cell cultures. J. Immunol. 149, 3525-3534. Schuler, G. and Steinman, R.M. (1985) Murine epidermal Langerhans cells mature into potent immunostimulatory dendritic cells in vitro. J. Exp. Med. 161,526-546. Shelley, W.B. and Juhlin, L. (1976) Langerhans cells form a reticuloepithelial trap for external contact allergens. Nature 261, 46-47. Shimada, S., Caughman, S.W., Sharrow, S.O., Stephany, D. and Katz, S.I. (1987) Enhanced antigenpresenting capacity of cultured Langerhans cells is associated with markedly increased expression of la antigen. J. lmmunol. 139, 2551-2555. Smith, C.A. and Rennick, D.M. (1986) Characterization of a murine lymphokine distinct from interleukin 3 (1L-3) possessing a T-cell growth factor activity and a mast cell growth factor activity that synergizes with IL-3. Proc. Natl. Acad. Sci. USA 83, 1857-1861. Steinman, R.M. (1991) The dendritic cell system and its role in immunogenicity. Annu. Rev. lmmunol. 9, 271-296. Streilein, J.W. and Grammer, S.F. (1989) In vitro evidence that Langerhans cells can adopt two functionally distinct forms capable of antigen presentation to T lymphocytes. J. Immunol. 143, 3925-3933. Tang, A. and Udey, M.C. (1991) Inhibition of epidermal Langerhans cell function by low dose ultraviolet B radiation: ultraviolet B radiation selectively modulates ICAM-I (CD54) expression by murine Langerhans cells. J. Immunol. 146, 3347-3355. Tepper, R.I., Levinson, D.A., Stanger, B.Z., Campos-Torres, J. Abbas, A.K. and Leder, P. (1990) IL-4 induces allergic-like inflammatory disease and alters T cell development in transgenic mice. Cell 62, 457-467. Thomson-Snipes, L., Dhar, V., Bond, M.W., Mosmann, T.R., Moore, K.W. and Rennick, D.M. (1991) Interleukin-10: a novel stimulatory factor for mast cells and their progenitors. J., Exp. Med. 173, 507-510. Trinchieri, G. (1993) Interleukin-12 and its role in the generation of THI cells. Immunol. Today 14, 335-338. van der Heijden, F.L., Wierenga, E.A., Bos, J.D. and Kapsenberg, M.L. (1991) High frequency of IL-4producing CD4+ allergen-specific T lymphocytes in atopic dermatitis lesional skin. J. Invest. Derm. 97, 389-394. Witmer-Pack, M.D., Olivier, W., Valinsky, J., Schuler, G. and Steinman, R.M. (1987) Granulocyte/macrophage colony-stimulating factor is essential for the viability and function of cultured murine epidermal Langerhans cells. J. Exp. Med. 166, 1484-1498. Yokota, T., Coffman, R.L., Hagiwara, H., Rennick, D.M., Takebe, Y. Yokota, K., Gemmell, L., Shrader, B., Yang, G., Meyerson, P., Luh, J., Hoy, P., Pene, J., Briere, F., Spits, H., Banchereau, J., De Vries, J., Lee, F.D., Arai, N. and Arai, K-I. (1987) Isolation and characterization of lymphokine cDNA clones encoding mouse and human IgA-enhancing and eosinophil-colony stimulating factor activities. Relationship to interleukin 5. Proc. Natl. Acad. Sci. USA 84, 7388-7392.
Toxicology 93 (1994) I - 11
Review article
Cytokines and regulation of allergic sensitization to chemicals * Ian Kimber Zeneca Central Toxicology Laboratory. Alderley Park, Uacclesfield, Cheshire, SK10 4TJ, UK
Received 3 October 1993; accepted 22 November
1993
Abstract Sensitization to chemicals and the elicitation of allergic reactions results from the stimulation of specific immune responses. Adaptive immunity is orchestrated by cytokines, a family of inducible glycoproteins that influence in many ways the behaviour of, and interaction between, cells which mediate immune and inflammatory responses. In this article the role of cytokines in the development of cutaneous immune responses to chemical allergens and in directing the quality of immune responses provoked by such materials is discussed.
Keywords: Cytokines; Chemical allergy; Dendritic cells; T lymphocytes
1. Introduction Allergy results from the exposure of susceptible individuals to sensitizing chemicals and is dependent upon the induction of specific immune responses. The nature of immune responses provoked by chemical allergens is essentially no different from that which characterizes protective immunity and provides host resistance against infectious disease. The immune system comprises a systemic network of tissues, cells *Presented
at the Second
1993. Elsevier Science Ireland Ltd. SSDI 0300-483X(94)02879-Y
Summer
School
in Immunotoxicology,
Beaune, France, 13-15 October
2
I. Kimber/Toxicology 93 (1994) 1-11
and molecules which must act in concert, and in an ordered fashion, to initiate and sustain adaptive immune responses. It is now apparent that normal immune function is orchestrated by cytokines; a diverse family of inducible glycoproteins, produced by various cell types, which mediate local interaction and distant communication between cellular elements of immune and inflammatory responses. Cytokines may act directly as inducers and regulators of cell growth, division and differentiation, as stimulators of cell movement and directed migration and as controllers of cell function and cellular interaction via induced changes in the expression of membrane determinants such as major histocompatibility complex antigens, adhesion molecules and receptors for cytokines themselves. The biology of cytokines is complex. They may act in endocrine, paracrine or autocrine fashion and may exhibit complementary, synergistic or antagonistic effects. The purpose of this article is to examine the role of cytokines in two aspects of the immune response to chemical allergens: (i) the role of epidermal cytokines and Langerhans cells during the induction phase of sensitization to chemicals encountered in the skin and (ii) the influence of T lymphocyte cytokines on the characteristics of immune responses to chemical allergens.
2. Epidermal cytokines, Langerhans cells and skin sensitization Langerhans cells (LCs) are members of the family of dendritic cells (DCs) - - bone marrow-derived cells characterized by possession of dendrites and a large surface area:volume ratio - - which are found in small numbers in lymphoid organs and in those tissues that come into closest apposition with the external environment (Steinman, 1991). LCs form a contiguous network in the epidermis where they are considered to serve as a trap for exogenous skin antigens (Shelley and Juhlin, 1976). Following topical exposure to skin sensitizing chemicals, DCs accumulate in the lymph nodes draining the site of contact. Many of the DCs which arrive in the nodes bear high levels of the inducing allergen. Indeed, during the first 24 h following skin sensitization all the cell-bound allergen found within draining nodes appears to be associated with DCs (Knight et al., 1985; Macatonia et ai., 1986, 1987; Kinnaird et al., 1989; Cumberbatch and Kimber, 1990; Kimber and Cumberbatch, 1992). The DCs which arrive in the lymph nodes derive from LCs which, in response to local sensitization, migrate from the skin and travel to the nodes via afferent lymphatics (Macatonia et al., 1987; Munn et al., 1989; Kripke et al., 1990; Kimbe'r and Cumberbatch, 1992). This process of LC movement and antigen transport is thought to be of central importance for the effective induction of skin sensitization. An interesting feature is that LCs resident within the epidermis are comparatively inefficient antigen presenting cells (Schuler and Steinman, 1985). However, following receipt of the stimulus to migrate and by the time of arrival in the draining nodes, LCs have acquired the characteristics of lymphoid DCs and are able efficiently to stimulate T cell activation. Thus, the antigen-bearing DCs found within local lymph nodes following skin sensitization are effective antigen presenting cells both in vitro (Knight et al., 1985; Macatonia et al., 1986; Jones et al., 1989; Robinson, 1989) and in vivo (Knight et al., 1985; Kinnaird et al., 1989; Macatonia and Knight, 1989).
1. Kimber / ToxiCOlogy:93 (1994J 1- I 1
3
Moreover, unlike epidermal LCs, the antigen-bearing DCs within draining nodes form stable clusters with T lymphocytes (Cumberbatch et al., 1991a). Langerhans cells in the skin are able to interact with and process foreign antigen (Streilein and Grammer, 1989). While in transit to the lymph nodes, however, this property is exchanged for immunostimulatory potential. The functional maturation of LCs into active antigen presenting cells is associated with and facilitated by an increased expression of several membrane determinants required for interaction with, and presentation of antigen to, T lymphocytes including major histocompatibility complex MHC class II (Ia) gene products (Cumberbatch et al., 1991b), intercellular adhesion molecule-1 (ICAM-1) (Cumberbatch et al., 1992) and the costimulatory molecule B7/BB1, a ligand for CD28 (Larsen et al., 1992). These events mirror in large part the changes to which LCs are subject during culture (Schuler and Steinman, 1985; Shimada et al., 1987; Witmer-Pack et al., 1987; Tang and Udey, 1991) and, by analogy with such in vitro studies, it is likely that granulocyte/macrophage colony-stimulating factor (GM-CSF), interleukin 1 (IL-1) and possibly other cytokines effect the functional maturation of LCs in vivo (WitmerPack et al., 1987; Heufler et al., 1988; Picut et al., 1988). The epidermis is a rich source of cytokines. In addition to GM-CSF and IL-1, epidermal cells (keratinocytes and Langerhans cells) produce, or can be stimulated to produce, a variety of cytokines including interleukins 6, 7, 8 and 10 (IL-6, IL-7, IL-8 and IL-10), macrophage inflammatory proteins lot and 2 (MIP-Ioc and MIP-2), tumour necrosis factor ot (TNF-Ot), transforming growth factors ot and/~ (TGF-Ot and TGF-/3) and interferon (IFN)-induced protein 10 (IP-10) (Barker, 1992; Enk and Katz, 1992a, b; Heufler et al., 1992). It is probable that epidermal cytokines are responsible not only for effecting the functional maturation of LCs during migration, but also for providing the stimulus for migration itself. Recent studies have demonstrated that TNF-Ot may represent an important stimulus for the movement of LCs from the epidermis following skin sensitization (Cumberbatch and Kimber, 1992; Cumberbatch et al., 1994). Consistent with the local availability ofcytokines being a requirement for the migration and maturation of LCs during skin sensitization is evidence that topical exposure of mice to contact allergens results in upregulation of epidermal mRNA for interleukin 1/3 (IL-1/~), IL-10, TNF-ot, GM-CSF and IP-10 (Enk and Katz, 1992a, b). The following sequence of events is therefore proposed to occur following skin contact with a chemical allergen. The sensitizing agent, either directly or indirectly, stimulates the increased synthesis and secretion of certain epidermal cytokines, including those known or suspected to influence LC behaviour. Tumour necrosis factor ot provides one signal for LC migration. Subsequently, GM-CSF and possibly other cytokines induce a functional and phenotypic maturation of LCs in transit to the lymph nodes such as to permit effective antigen presentation and the initiation of T lymphocyte responses. Langerhans cells and DCs were considered originally not to produce cytokines. It is of some interest, therefore, that recent investigations have shown LCs to be the major or exclusive source within the epidermis of IL-I~ (Enk and Katz, 1992a; Heufler et al., 1992; Matsue et al., 1992; Schreiber et al., 1992) and MIP-lot (Heufler et al., 1992; Matsue et al., 1992). Furthermore, there is evidence that the expression
4
L Kimber / Toxicology 93 (1994) 1-11
Table 1 Epidermal cytokine expression by murine Langerhans cells Cytokine
Selective expression by LCs
Expression by keratinocytes
Modulationduring culture of LCs
Interleukin i/3 (IL-I/3) Macrophage inflammatoryprotein l a
+ +
-
Increased Decreased
-
+
Decreased
-
+
Increased
(MIP-i~)
Macrophage inflammatoryprotein 2 (MIP-2) Interleukin 6 (IL-6)
Data from Enk and Katz (1992a), Heufler et al. (1992), Matsue et al. (1992) and Schreiber et al. (1992).
of cytokines by LCs is modulated differentially during culture, a process which can be considered equivalent to the functional maturation of these cells in vivo. Expression of IL-1/3 is upregulated strongly following culture of LCs, while m R N A for MIP-lc~ (and MIP-2) is decreased (Heufler et al., 1992). In addition, cultured LCs produce IL-6 (Heufler et al., 1992; Schreiber et al., 1992) (Table 1). With regard to the acquisition by LCs of immunostimulatory and antigen presenting potential it may be relevant that culture is associated with an increased expression of two cytokines (IL-1/3 and IL-6) which are known to act as important costimulatory molecules for T lymphocyte activation. The significance of LC-derived MIP-Ic~ and the downregulation of this cytokine during culture is uncertain, although it has been suggested that this molecule serves as a paracrine regulator of keratinocyte stem cell development in the skin (Heufler et al., 1992). The expression of certain epidermal cytokines is increased in response to various types of cutaneous stimuli. Thus, for example, it is known that skin sensitizers, skin irritants and local irradiation with ultraviolet (UV) light all induce the increased production of epidermal TNF-c~ (Kock et al., 1990; Enk and Katz, 1992a). It has been demonstrated, however, that the upregulation of some epidermal cytokines is provoked selectively by chemical allergens. Enk and Katz (1992a, b) have shown that topical exposure of mice to chemical allergens such as dinitrofluorobenzene
Table 2 Selective upregulation of certain epidermal cytokines by chemical allergens Cytokine Interleukin 1/3 (IL-I/3) lnterleukin 10 (IL-10) Interferon-induced protein 10 (IP-10) Macrophage inflammatoryprotein 2 (MIP-2)
Source Langerhans cells
Keratinocytes
--
+
--
+
+
+
Taken from Enk and Katz (1992a, b) and Heufler et al. (1992).
L Kirnber / Toxicology 93 (1994) 1-11
5
(DNFB), but not to skin irritants, induces increased epidermal cell mRNA for IL-1/3, IL-10, MIP-2 and IP-10 (Table 2). Interleukin 1/3 is of particular interest. This cytokine is expressed solely by LCs within the epidermis and production is increased in situ by chemical allergens and also during the maturation of LCs into immunostimulatory DCs. It has been found recently that intradermal injection of mice with IL-1/~causes a rapid and significant increase in epidermal mRNA for a number of cytokines including TNF-a (Enk et al., 1993). Moreover, skin sensitization was shown to be inhibited if the availability of local IL-1/~was reduced (Enk et al., 1993). On the basis of these data it may be that an early and essential event during the induction phase of contact sensitization is the stimulation of IL-I~ production by LCs which in turn induces the release of keratinocyte-derived cytokines necessary for LC migration and maturation. Although uncertainties remain, the importance of epidermal cytokines for the initiation of cutaneous immune responses is beyond doubt. Further work should provide a detailed picture of the molecular interactions which are induced in the skin by chemical allergens and which result in the development of contact sensitization.
3. T helper cells, cytokines and allergic responses Some chemical sensitizers are able to cause occupational respiratory allergy, while others are contact allergens but fail to induce pulmonary hypersensitivity. The type of sensitization caused by chemicals, and the form allergic reactions will take following subsequent re-exposure of a sensitized individual, is to a large extent governed by the quality of immune responses induced. Immune effector mechanisms can be divided broadly into cell-mediated and humoral (antibody-mediated) reactions. Both play important roles in allergic responses. Contact hypersensitivity, one form of delayed-type hypersensitivity reaction, is effected by a cell-mediated immune response in which T lymphocytes play a central role. In contrast, immediate-type hypersensitivity reactions, such as those that characterize the acute onset of respiratory allergy, are provoked by antibody, and in particular by antibody of the IgE class. In considering the relationship between cell-mediated and humoral processes in the development of immune responses the activity of T helper cells and the cytokines they elaborate are of particular relevance. T helper (Th) cells, defined by possession of the membrane determinant CD4, promote immune responses and cooperate with B lymphocytes in the generation of antibody responses. In 1986 it was demonstrated that in mice there exists a functional heterogeneity among CD4 ÷ Th cells. Two main classes were recognized and designated Thl and Th2 (Mosmann et al., 1986). These populations differ with respect to their cytokine products. In mice both populations produce interleukin 3 (IL-3) and GM-CSF. However, only Thl cells secrete interleukin 2 (IL-2), interferon 3' (IFN-3') and tumour necrosis factor/3 (TNF-/3; lymphotoxin) and only Th2 cells produce interleukins 4, 5, 6 and 10 (IL-4, IL-5, IL-6 and IL-10) (Mosmann and Coffman, 1989; Mosmann et al., 1991) (Table 3). A similar, but not identical, heterogeneity among human Th cells has now been described also (Romagnani, 1991). The relevance of Th cell subpopulations to the development of allergic disease is that their soluble products exert opposing regula-
6
L Kirnber/Toxicology 93 (1994) 1-11
Table 3 Cytokine secretion by murine Th I and Th2 cells Cytokine
Thl cells
Th2 cells
Interleukin 3 (IL-3) Granulocyte/macrophagecolony-stimulatingfactor (GM-CSF) Interferon-3,(IFN-3,) lnterleukin 2 (IL-2) Tumour necrosis factor B (TNF-#; lymphotoxin) Interleukin 4 (IL-4) lnterleukin 5 (1L-5) lnterleukin 6 (IL-6) interleukin 10 (IL-10)
+ +
+ +
+ + + -
+ + + +
Taken from Mosmann et al. (1991).
tory effects on IgE production and on other aspects of allergic processes. The induction of IgE responses in mice is dependent upon IL-4 (Finkelman et al., 1988a). Mice homozygous for a mutation that inactivates the gene for IL-4 lack detectable IgE and fail to mount IgE responses (Kuhn et al., 1991), while mice which possess a transgene for the cytokine and constitutively produce high levels of IL-4 exhibit increased concentrations of serum IgE (Tepper et al., 1990; Burstein et al., 1991). In contrast, IFN-3,, a product of Thl cells, antagonizes the production of IgE antibody (Finkelman et al., 1988b). In man, also, these cytokines regulate reciprocally the synthesis of IgE (Del Prete et al., 1988; Pene et al., 1988). The initiation of IgE responses and the development of immediate-type hypersensitivity will be favoured, therefore, by allergens, or conditions of exposure to allergens, which result in a preferential stimulation of Th2-type responses. The selective activation of Th 1 cells will not normally be permissive for IgE production. Th ltype immune responses are, however, compatible with the induction by chemical allergens of contact sensitization. It has been found that delayed-type hypersensitivity responses are effected by Thl cells. (Cher and Mosmann, 1987), and that IFN-3, plays an important role in this process (Diamanstein et al., 1988; Fong and Mosmann, 1989). Consistent with the stimulation of preferential Th cell activation by contact and respiratory sensitizers are the characteristics of immune responses provoked in mice by chemical allergens. Topical exposure of mice to respiratory chemical allergens, such as trimellitic anhydride and phthalic anhydride, results in strong IgE responses. In contrast, under the same conditions of exposure, contact allergens known or suspected not to cause respiratory hypersensitivity (such as dinitrochlorobenzene and oxazolone) fail to elicit an IgE response but do provoke comparatively high levels of IgG2a antibody, an isotype known to be stimulated by IFN-3, (Dearman and Kimber, 1991, 1992; Dearman et al., 1992). It can be suggested therefore that the physico-chemical properties of the allergen itself, or the way in which it is handled, processed and presented will determine the characteristics of the immune response induced and the type of allergic reaction that will be provoked following subsequent challenge.
I. Kimber / Toxicology 93 (1994) 1-11
7
Cytokines appear also to play an important role in the initial generation of divergent Th cell subpopulations themselves. Th cells displaying a phenotype of selective cytokine synthesis develop as the immune system matures. It has been shown that IL-4 favours the development of Th2 cells, while IFN-~, promotes Thl cells (Coffman et al., 1991; Abehsira-Amar et al., 1992; Gross et al., 1993; Kopf et al., 1993). Cellular vectors of the natural immune system, mast cells and natural killer (NK) cells, may be the source of these cytokines (IL-4 and IFN-~, respectively) during the early stages of an adaptive immune response prior to the appearanCe of differentiated Thl and Th2 cells (Romagnani, 1992). Other cytokines, such as IL-12 (IL-12) (Trinchieri, 1993) and IL-10 (Hsieh et al., 1992) may also be promotors, respectively, of Thl and Th2 cell development. In addition to regulating the production of IgE antibody and controlling the development of Th subpopulations, the soluble products of Th I and Th2 cells influence in other ways the allergic response. Interleukins 3, 4 and 10 are all mast cell growth factors or cofactors (Smith and Rennick, 1986; Thomson-Snipes et al., 1991) and I L5 is a growth and differentiation factor for eosinophils (Yokota et al., 1987). Moreover, IL-4 will enhance the secretory potential of mast cells in vitro (Coleman et al., 1992, 1993). Here again IFN-~, has a reciprocal effect and serves to reduce serotonin release by mast cells activated in culture (Coleman et al., 1991, 1992, 1993). The severity of local allergic reactions may be influenced in other ways by cytokines. Interleukin 5 controls the accumulation of eosinophils at the site of allergen-induced respiratory reactions (Chand et al., 1992; Gulbenkian et al., 1992; Iwami et al., 1992, 1993), a process antagonized by IFN-~ (Iwamoto et al., 1993). In addition, IL-4 has been shown to depress dermal contact hypersensitivity reactions (Gautam et ai., 1992). Divergent Th cell responses also characterize human allergic disease. Clones of T lymphocytes derived from the peripheral blood of nickel sensitive donors secrete IFN-~,, but only low or undetectable levels of Th2 cytokines (Kapsenberg et al., 1991, 1992). In contrast, T cell clones specific for aeroallergens which induce in man IgE-mediated hypersensitivity reactions have been shown to produce Th2 cytokines but not IFN-~, (Parronchi et al., 1991). Also, CD4 ÷ T cell clones prepared from lesional skin biopsies of house dust mite-allergic atopic donors were found to be of Th2 phenotype on the basis of cytokine production (van der Heijden et al., 1991). A predominance of Th2-type cells in the sites of cutaneous reactions in atopic individuals has been demonstrated also by in situ hybridization. Cells infiltrating lesional skin expressed mRNA for IL-3, IL-4, IL-5 and GM-CSF, but not for IFN-~, (Kay et al., 1991). Finally, it should be emphasized that other cytokines may also influence IgE antibody responses. It has been suggested that interleukin 9 (IL-9) may potentiate IL-4-induced IgE synthesis (Petit-Frere et al., 1993) and that a recently characterized product of T lymphocytes, interleukin 13 (IL-13), is able to induce an IL-4independent synthesis of IgE by human B lymphocytes (Punnonen et al., 1993). The available data indicate therefore that cytokines, and more particularly the relative availability of cytokines, influence not only the development of allergic responses but also the hypersensitivity reactions that are provoked by exposure to
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allergen in sensitized individuals. The induction of Th2-type responses will promote immediate type hypersensitivity. The products of activated Th2 cells stimulate IgE production, serve as growth factors for mast cells and eosinophils and as potentiators of mast cell function, promote the accumulation of eosinophils at inflammatory sites and will encourage the further development of Th2 cells themselves. In contrast, preferential Th 1-type responses will favour cell-mediated immunity and the development of contact hypersensitivity. Interferon-7 produced by Thl cells antagonizes IgE responses, downregulates mast cell function and inhibits other aspects of immediate type hypersensitivity reactions. Moreover, IFN-7 stimulates the generation of Thl cells. Other cytokines, and other regulatory cells and molecules, influence the initiation of IgE responses and allergic processes. It is apparent, however, that the products of differentiated Th cells play a central, and probably decisive, role in determining the characteristics of immune responses that will be provoked by exposure to chemical allergens. References Abehsira-Amar, O., Gibert, M., Joliy, M., Theze, J. and Jankovic, D.L. (1992) IL-4 plays a dominant role in the differential development of Tho into Thl and Th2 cells. J. Immunol. 148, 3820-3829. Barker, J.N.W.N. (1992) Role of keratinocytes in allergic contact dermatitis. Contact Derm. 26, 145-148. Burstein, H.J., Tepper, R.I., Leder, P. and Abbas, A.K. (1991) Humoral immune functions in IL-4 transgenic mice. J. Immunol. 147, 2950-2956. Chand, N., Harrison, J.E., Rooney, S., Pillar, J., Jakubicki, R., Nolan, K. Diamantis W. and Sofia, R.D. (1992) Anti-IL-5 monoclonal antibody inhibits allergic late phase bronchial eosinophilia in guinea pigs: a therapeutic approach. Eur. J. Pharmacol. 211, 121-124. Cher, D.J. and Mosmann, T.R. (1987) Two types of murine helper T cell clone. 1I. Delayed type hypersensitivity is mediated by Thl clones. J. Immunol. 138, 3688-3694. Coffman, R.L., Varkila, K., Scott, P. and Chatelain, R. (1991) Role of cytokines in the differentiation of CD4+ T-cell subsets in vivo. Immunol. Rev. 123, 189-207. Coleman, J.W., Buckley, M.G., Holliday, M.R. and Morris, A.G. (1991) Interferon-y inhibits serotonin release from mouse peritoneal mast cells. Eur. J. Immunol. 21, 2559. Coleman, J.W., Holliday, M.R. and Buckley, M.G. (1992) Regulation of the secretory function of mouse peritoneal mast cells by IL-3, IL-4 and IFN-% int. Arch. Allergy Immunol. 99, 408-410. Coleman, J.W., Holliday, M.R., Kimber, I., Zsebo, K.M. and Galli, S.J. (1993) Regulation of mouse peritoneal mast cell secretory function by stem cell factor, IL-3 or IL-4. J. Immunol. 150, 556-562. Cumberbatch, M. and Kimber, 1. (1990) Phenotypic characteristics of antigen bearing cells in the draining lymph nodes of contact sensitized mice. Immunology 71,404-410. Cumberbatch, M. and Kimber, I. (1992) Dermal tumonr necrosis factor-a induces dendritic cell migration to draining lymph nodes, and possibly provides one stimulus for Langerhans cell migration. Immunology 75, 257-263. Cumberbatch, M., lllingworth, I. and Kimber, I. (1991a) Antigen-bearing dendritic cells in the draining lymph nodes of contact sensitized mice. Cluster formation with lymphocytes. Immunology 74, 139-145. Cumberbatch, M., Gould, S.J. Peters, S.W. and Kimber, 1. (1991b) MHC class II expression by Langerhans cells and lymph node dendritic cells: possible evidence for maturation of Langerhans cells following contact sensitization. Immunology 74, 414-419. Cumberbatch, M., Peters, S.W., Gould, S.J. and Kimber, 1. (1992) Intercellular adhesion molecule-I (ICAM-1) expression by lymph node dendritic cells. Comparison with epidermal Langerhans cells. lmmunol. Lett. 32, 105-110.
L Kimber / Toxicology 93 (1994) 1-11
9
Cumberbatch, M., Fielding, I. and Kimber, I. (1994) Modulation of epidermal Langerhans cell frequency by tumour necrosis factor c~ (TNF-ct). Immunology 81, 395-401. Dearman, R.J. and Kimber, I. (1991) Differential stimulation of immune function by respiratory and contact chemical allergens. Immunology 72, 563-570. Dearman, R.J. and Kimber, I. (1992) Divergent immune responses to respiratory and contact chemical allergens: antibody elicited by phthalic anhydride and oxazolone. Clin. Exp. Allergy 22, 241-250. Dearman, R.J., Basketter, D.A., Coleman, J.W. and Kimber, 1. (1992) The cellular and molecular basis for divergent allergic responses to chemicals. Chem.-Biol. Interact. 84, 1-10. Del Prete, G., Maggi, E., Parronchi, P., Chretien, 1., Tiri, D., Macchia, M., Ricci, J., Banchereau, J., De Vries, J. and Romagnani, S. (1988) 1L-4 is an essential factor for the IgE synthesis induced in vitro by human T cell clones and their supernatants. J. Immunol. 140, 4193-4198. Diamanstein, T., Eckert, R., Volk, H-D. and Kupier-Weglinski, J-W. (1988) Reversal by interferon-'y of inhibition of delayed-type hypersensitivity induction by anti-CD4 or anti-interleukin 2 receptor (CD25) monoclonal antibodies. Evidence for the physiological role of CD4+ Thl+ subset in mice. Eur. J. Immunol. 18, 2101-2103. Enk, A.H. and Katz, S.I. (1992a) Early molecular events in the induction phase of contact sensitivity. Proc. Natl. Acad. Sci, USA 89, 1398-1402. Enk, A.H. and Katz, S.I. (1992b) Identification and induction of keratinocyte derived IL-10. J. lmmunol. 149, 92-95. Enk, A.H., Angeloni, V.L., Udey, M.C. and Katz, S.I. (1993) An essential role for Langerhans cellderived IL-I/~ in the initiation of primary immune responses in the skin. J. lmmunol. 150, 3698-3704. Finkelman, F.D., Katona, I.M., Urban Jr. J,F., Holmes, J., Ohara, J. Tung, A.S., Sample, J.G. and Paul, W.E. (1988a) IL-4 is required to generate and sustain in vivo lgE responses. J. lmmunol. 144, 2335-2341. Finkelman, F.D., Katona, I.M., Mosmann, T.R. and Coffman, R.L. (1988b) I FN-3, regulates the isotypes of lg secreted during in vivo humoral immune responses. J. lmmunol. 140, 1022-1027. Fong, T.A.T. and Mosmann, T.R. (1989) The role of IFN-'t in delayed-type hypersensitivity mediated by Thl clones. J. Immunol. 143, 2887-2893. Gautam, S.C., Chikkala, N.F. and Hamilton, T.A. (1992) Anti-inflammatory action of 1L-4. Negative regulation of contact sensitivity to trinitrochlorobenzene. J., Immunol. 148, 1411-1415. Gross, A., Ben-Sasson, S.Z. and Paul, W.E. (1993) Anti-IL-4 diminishes in vivo priming for antigenspecific IL-4 production by T cells. J. Immunol. 150, 2112-2120. Gulbenkian, A.R., Egan, R.W., Fernandes, X., Jones, H., Kreutner, W. Kung, T., Payvandi, F., Sullivan, L., Zurcher, J.A. and Watnik, A.S. (1992) Interleukin-5 modulates eosinophil accumulation in allergic guinea pig lung. Am. Rev. Respir. Dis. 146, 263-268. Heufler, C. Koch, F. and Schuler, G. (1988) Granulocyte/macrophage colony stimulating factor and interleukin 1 mediate the maturation of murine epidermal Langerhans cells into potent immunostimulatory dendritic cells. J. Exp. Med. 167, 700-705. Heufler, C., Topar, G., Koch, F., Trockenbacher, B., Kampgen, E. Romani, N. and Schuler, G. (1992) Cytokine gene expression in murine epidermal cell suspensions: interleukin 1/3 and macrophage inflammatory protein lc~ are selectively expressed in Langerhans cells but are differentially regulated in culture. J. Exp. Med. 176, 1221-1226. Hsieh, C-S., Heimberger, A.B., Gold, J.S., O'Garra, A. and Murphy, K.M. (1992) Differential regulation of T helper phenotype development by interleukin 4 and 10 in an c~ T-cell-receptor transgenic system. Proc. Natl. Acad. Sci. USA 89, 6065-6069. lwami, T., Nagai, H., Suda, H., Tsuruoka, N. and Koda, A. (1992) Effect of murine recombinant interleukin-5 on the cell population in the guinea-pig airways. Br. J. Pharmaco|. 195, 19-22. Iwami, T., Nagai, H., Tsuruoka, N. and Koda, A. (1993) Effect of murine recombinant interleukin-5 on bronchial reactivity in guinea pigs. Clin. Exp. Allergy 23, 32-38. Iwamoto, I., Nakajima, H., Endo, H. and Yoshida, S. (1993) Interferon -/ regulates antigen-induced eosinophil recruitment into the mouse airways by inhibiting the infiltration of CD4+ T cells. J. Exp. Med. 177, 573-576. Jones, D.A., Morris, A.G. and Kimber, !. (1989) Assessment of the functional activity of antigen-bearing
10
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dendritic cells isolated from the lymph nodes of contact-sensitized mice. Int. Arch. Allergy Appl. lmmunol. 90, 230-236. Kapsenberg, M.L., Wierenga, E.A., Bos, J.D. and Jansen, H.M. (1991) Functional subsets of allergenreactive human CD4 ÷ T cells. Immunol. Today 12, 392-395. Kapsenberg, M.L., Wierenga, E.A., Stiekma, F.C.M., Tiggelman, A.M.B.C. and Bos, J.D. (1992) Thl lymphokine production profiles of nickel-specific CD4+ T lymphocyte clones from nickel contact allergic and non-allergic individuals. J. Invest. Derm. 98, 59-63. Kay, A.B., Ying, S., Varney, V., Gaga, M., Durham, S.R., Moqbel, R. Wardlaw, A.J. and Hamid, Q (1991) Messenger RNA expression of the cytokine gene cluster, interleukin 3 (IL-3), IL-4, IL-5 and granulocyte/macrophage colony stimulating factor, in allergen-induced late phase cutaneous reactions in atopic subjects. J. Exp. Med. 173, 775-778. Kimber, I. and Cumberbatch, M. (1992) Dendritic cells and cutaneous immune responses to chemical allergens. Toxicol. Appl. Pharmacol. 117, 137-146. Kinnaird, A., Peters, S.W., Foster, J.R. and Kimber, I. (1989) Dendritic cell accumulation in the draining lymph nodes during the induction phase of contact allergy in mice. Int. Arch. Allergy Appl. Immunol. 89, 202-210. Knight, S.C., Krejci, J., Malkovsky, M., Colizzi, V., Gautam, A. and Asherson, G.L. (1985) The role of dendritic cells in the initiation of immune responses to contact sensitizers. I. In vivo exposure to antigen. Cell. lmmunol. 94, 427-434. Kock, A., Schwarz, T., Kirnbauer, R., Urbanski, A., Perry, P. Ansel, J.C. and Luger, T.A. (1990) Human keratinocytes are a source for tumour necrosis factor tx: evidence for synthesis and release upon stimulation with endotoxin or ultraviolet light. J. Exp. Med. 172, 1609-1614. Kopf, M., Le Gros, G., Bachmann, M., Lamers, M.C., Bluethmann, H. and Kohler, G. (1993) Disruption of the murine IL-4 gene blocks Th2 cytokine synthesis. Nature 362, 245-248. Kripke, M.L., Munn, C.G., Jeevan, A., Tang, J-M. and Bucana, C. (1990) Evidence that cutaneous antigen-presenting cells migrate to regional lymph nodes during contact sensitization. J. lmmunol. 145, 2833-2838. Kuhn, R., Rajewsky, K. and Muller, W. (1991) Generation and analysis of interleukin-4 deficient mice. Science 254, 707-710. Larsen, C,P., Ritchie, S.C., Pearson, T.C., Linsley, P.S. and Lowry, R.P. (1992) Functional expression of the costimulatory molecule, B7/BBI, on murine dendritic cell populations. J. Exp. Med. 176, 1215-1220. Macatonia, S.E. and Knight, S.C. (1989) Dendritic cells and T cells transfer sensitization for delayed-type hypersensitivity after skin painting with contact sensitizer. Immunology 66, 96-99. Macatonia, S.E., Edwards, A.J. and Knight, S.C. (1986) Dendritic cells and the initiation of contact sensitivity to fluorescein isothiocyanate. Immunology 59, 509-514. Macatonia, S.E., Knight, S.C., Edwards, A.J., Griffiths, S. and Fryer, P. (1987) Localization of antigen on lymph node dendritic cells after exposure to the contact sensitizer fluorescein isothiocyanate. Functional and morphological studies. J. Exp. Med. 166, 1654-1667. Matsue, H., Cruz Jr. P.D., Bergstresser, P.R. and Takashima, A. (1992) Langerhans cells are the major source ofmRNA for IL-IB and MIP-la among unstimulated mouse epidermal cells. J. Invest. Derm. 99, 537-541. Mosmann, T.R. and Coffman, R.L. (1989) Heterogeneity of cytokine secretion patterns and functions of helper T cells. Adv. lmmunol. 46, 111-147. Mosmann, T.R., Cherwinski, H., Bond, M.W., Giedlin, M.A. and Coffman, R.L. (1986) Two types of murine helper T cell clone. I. Definition according to profiles of lymphokine activities and secreted proteins. J. immunol. 136, 2348-2357. Mosmann, T.R., Schumacher, J.H., Street, N.F., Budd, R., O'Garra, A. Fong, T.A.T., Bond, M.W. Moore, K.W.M., Sher, A. and Fiorentino, D.F. (1991) Diversity of cytokine synthesis and function of mouse CD4+ T cells. Immunol. Rev. 123, 209-229. Munn, C.G. Bucana, C. and Kripke, M.L. (1989) Antigen-binding cells from lymph nodes of mice sensitized epicutaneously with hapten have features of epidermal Langerhans cells. J. Invest. Derm. 92, 487. Parronchi, P., Macchia, D., Piccinni, M-P., Biswas, P., Simonelli, C. Maggi, E., Ricci, M., Ansari, A.A.
1. Kimber / Toxicology 93 (1994) 1-11
11
and Romagnani, S. (1991) Allergen and bacterial antigen-specific T-cell clones established from atopic donors show a different profile of cytokine production. Proc. Natl. Acad. Sci. USA 88, 4538-4542. Pene, J., Rousset, F., Briere, F., Chretien, 1., Paliard, X., Banchereau, J. Spits, H. and De Vries, J.E. (1988) IgE production by normal human B cells induced by alloreactive T cell clones is mediated by IL-4 and suppressed by 1FN~. J. lmmunol. 141, 1218-1224. Petit-Frere, C., Dugas, B., Braquet, P. and Mencia-Huerta, J.M. (1993) lnterleukin-9 potentiates the interleukin-4-induced IgE and lgGl release from murine B lymphocytes. Immunology 79, 146-151. Picut, C.A., Lee, C.S., Dougherty, E.P., Anderson, K.L. and Lewis, R.M. (1988) lmmunostimulatory capabilities of highly enriched Langerhans cells in vitro. J. Invest. Derm. 90, 201-206. Punnonen, J., Aversa, G., Cocks, B.G., McKenzie, A.N.J., Menon, S. De Waal Malefyt, R. and De Vries, J.E. (1993) Interleukin 13 induces interleukin 4-independent IgG4 and IgE synthesis and CD23 expression by human B cells. Proc. Natl. Acad. Sci. USA 90, 3730-3734. Robinson, M.K. (1989) Optimization of an in vitro lymphocyte blastogenesis assay for predictive assessment of immunologic responsiveness to contact sensitizers. J. Invest. Derm. 92, 860-867. Romagnani, S. (1991) Human THI and TH2 subsets: doubt no more. lmmunol. Today 12, 256-257. Romagnani, S. (1992) Induction of THI and TH2 responses: a key role for the "natural' immune responses. Immunol. Today 13, 379-381. Schreiber, S., Kilgus, O., Payer, E., Kutil, R., Elbe, A., Mueller, C. and Stingl, G. (1992) Cytokine pattern of Langerhans cells isolated from murine epidermal cell cultures. J. Immunol. 149, 3525-3534. Schuler, G. and Steinman, R.M. (1985) Murine epidermal Langerhans cells mature into potent immunostimulatory dendritic cells in vitro. J. Exp. Med. 161,526-546. Shelley, W.B. and Juhlin, L. (1976) Langerhans cells form a reticuloepithelial trap for external contact allergens. Nature 261, 46-47. Shimada, S., Caughman, S.W., Sharrow, S.O., Stephany, D. and Katz, S.I. (1987) Enhanced antigenpresenting capacity of cultured Langerhans cells is associated with markedly increased expression of la antigen. J. lmmunol. 139, 2551-2555. Smith, C.A. and Rennick, D.M. (1986) Characterization of a murine lymphokine distinct from interleukin 3 (1L-3) possessing a T-cell growth factor activity and a mast cell growth factor activity that synergizes with IL-3. Proc. Natl. Acad. Sci. USA 83, 1857-1861. Steinman, R.M. (1991) The dendritic cell system and its role in immunogenicity. Annu. Rev. lmmunol. 9, 271-296. Streilein, J.W. and Grammer, S.F. (1989) In vitro evidence that Langerhans cells can adopt two functionally distinct forms capable of antigen presentation to T lymphocytes. J. Immunol. 143, 3925-3933. Tang, A. and Udey, M.C. (1991) Inhibition of epidermal Langerhans cell function by low dose ultraviolet B radiation: ultraviolet B radiation selectively modulates ICAM-I (CD54) expression by murine Langerhans cells. J. Immunol. 146, 3347-3355. Tepper, R.I., Levinson, D.A., Stanger, B.Z., Campos-Torres, J. Abbas, A.K. and Leder, P. (1990) IL-4 induces allergic-like inflammatory disease and alters T cell development in transgenic mice. Cell 62, 457-467. Thomson-Snipes, L., Dhar, V., Bond, M.W., Mosmann, T.R., Moore, K.W. and Rennick, D.M. (1991) Interleukin-10: a novel stimulatory factor for mast cells and their progenitors. J., Exp. Med. 173, 507-510. Trinchieri, G. (1993) Interleukin-12 and its role in the generation of THI cells. Immunol. Today 14, 335-338. van der Heijden, F.L., Wierenga, E.A., Bos, J.D. and Kapsenberg, M.L. (1991) High frequency of IL-4producing CD4+ allergen-specific T lymphocytes in atopic dermatitis lesional skin. J. Invest. Derm. 97, 389-394. Witmer-Pack, M.D., Olivier, W., Valinsky, J., Schuler, G. and Steinman, R.M. (1987) Granulocyte/macrophage colony-stimulating factor is essential for the viability and function of cultured murine epidermal Langerhans cells. J. Exp. Med. 166, 1484-1498. Yokota, T., Coffman, R.L., Hagiwara, H., Rennick, D.M., Takebe, Y. Yokota, K., Gemmell, L., Shrader, B., Yang, G., Meyerson, P., Luh, J., Hoy, P., Pene, J., Briere, F., Spits, H., Banchereau, J., De Vries, J., Lee, F.D., Arai, N. and Arai, K-I. (1987) Isolation and characterization of lymphokine cDNA clones encoding mouse and human IgA-enhancing and eosinophil-colony stimulating factor activities. Relationship to interleukin 5. Proc. Natl. Acad. Sci. USA 84, 7388-7392.