The regulation of gastrointestinal immune responses

156

immt~nology lo@', A~g~.rl 198/

cigarette smoke is due to oxidation reactions 9. The report indicates that inactivation of %-antitrypsin depended in part on O> H 2 0 2 and myeloperoxidase. Monocytes and leucocytes from patients with chronic granulomatous disease, in whom the generation of O 2 and H 2 0 2 are depressed, did not inactivate the antiprotease after exposure to PMA. The effect of cigarette smoke on alveolar macrophage activity suggests that these cells produce reactive oxygen species which should result in enhanced inactivation References 1 Morse, J. O. (1978) .N. Eng/. J. Med. 299, 1045-1048; 1099-1105 2 ,Janoff, A., White, R., Carp, H., tfarel, S., Dearing, R. and Lee, D. (1979) Am.J. l°ntaol. 97, 111-136 3 Merrill, W. W., Naegel, G. P., Matthay, R. A. and Reynolds, tl. Y. (1980),7. C/in. Irtve.~/.65,268-276 4 Gadek, J. E., Hunninghake, G. W., Zimmerman, R. L. and Crystal, R. G. (1980) Am. Re¢~.Re.@r. Dis. 121,723-733

of antiproteases leading to increased destruction of alveolar connective tissue. It appears from these studies that alveolar macrophages and leucocytes are largely responsible for the generation of emphysema. Exposure to cigarette smoke has a profound effect on t h e hemostatic mechanisms of the lung leading to emphysema. BRUCE

S. Z ' W 1 L L I N G

Depar/ment ~!fMicrobiology, Od/ege ~!/"Biologica! Sciences and Comprehens'iz,e Caneer (>,let, The Ohir; S/ale University, Odumbus, OH d3210, U.S.A.

5 Hunninghake, G. W., Davidson,j. M., Rennard, S., Szapiel, S., Gadek,.J.E. and Crystal, R. G. (19811 Science 212, 925-927 6 Janoff, A., Carp. H., Lee, 1). K. and Drew, R. T. (19791 Science 206, 1313-1314 7 Gadek, J. E., Fellis, G. A. and Crystal, R. G. (1979) &ience 206, 1315 1316 8 Carp, It. andJanoff, A. (19801,7. (Yi,. I, vesl. 66, 987-995 9 Carp, H. andJanoff, A. (1978) Am. Rev. Respir. Dis 118,617-621

) The regulation of gastrointestinal immune responses Warren Strober, Lee K. Richman and Charles O. Elson hnmunophysiology Section, Metabolism Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20205, U.S.A. The antigenic environment of the mucosal i m m u n e system differs from that of the systemic i m m u n e system. The mucosae are in constant contact with a myriad of substances that have readily demonstrable i m m u n o s t i m u l a t o r y or i m m u n o m o d u l a t o r y properties and within such an environment lymphoid tissue could conceivably undergo excessive stimulation. As a result responses to potentially pathogenic stimuli might be pre-empted by responses to an overwhelming array of inconsequential materials. For this reason it would not be surprising to find that the mucosal i m m u n e system had regulatory mechanisms allowing it to react selectively to m a n y or most substances found in the mucosal environment. It is reasonable to suppose that such mechanisms would be mediated by cellular components that differ qualitatively a n d / o r quantitatively from those found elsewhere in the i m m u n e system (see Fig. i ). In the following review, we will discuss mucosal i m m u n e responses from an i m m u n o r e g u l a t o r y viewpoint. We shall first consider studies ,in which ¢ Else~i(J/North I lolland Biomcdica~ Press 1981 0167

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antigen feeding fails to result in i m m u n i z a t i o n and, instead, induces unresponsiveness (tolerance) to subsequent challenge with the antigen. We shall then consider studies in which antigen feeding results in immunization as well as priming of the animal for secondary antibody responses. Finally, we will discuss studies of a mechanism by which the mucosal i m m u n e system can compartmentalize its regulation of a response, so that simultaneous e n h a n c e m e n t and suppression can be obtained, depending on the Ig class of the induced responses. Such a mechanism is indicative of the complexity of mucosal i m m u n o r e g u l a t i o n and provides evidence that regulation in this area may have several unique features. M e c h a n i s m s of oral u n r e s p o n s i v e n e s s (tolerance) Suppre.rsiorz of oral res~Jm~.sesby 13 cells or B-cell products

Oral unresponsiveness was first studied within the context of modern immunology by Chase in 1946, although related observations were made as early as the mid-nineteenth century ~. Chase showed that after

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Fig. 1. Diagrammatic representation of antigenic stimulation occurring in the mucosal immune system. The gut lumen is filled with antigenic material (A) which gains entry to organized gut lymphoid tissues such as tl']e Peyer's patches, tlere the encounter B ceils as well as regulatory T cells which can migrate to draining lymphoid tissues (mesenteric lymph node) and then to the systemic and mucosal circulations. Both helper and suppressor T cells may be stimulated in the Payer's patch and this may account for the fact that both responsiveness and unresponsivenesscan followantigen feeding.

guinea pigs were fed with a chemically simple skinsensitizing substance, dinitrochlorobenzene (DNCB), they did not show contact s e n s i t i z a t i o n with this material. This p h e n o m e n o n has been recently reinvestigated by Asherson e! a/., who studied the e q u i v a l e n t u n r e s p o n s i v e n e s s which follows oral challenge of rats with the skin-sensitizing agents oxazalone and picryl chloridC. These investigators showed, in cell-transfer studies, that unresponsiveness was associated with the development of (1) suppressor B cells capable of suppressing skin reactivity in recipient animals which had been transferred in suspensions of lymph-node or spleen cells obtained from skin-sensitized animals; and (2) suppressor T cells capable of suppressing DNA proliferation of lymph-node cells of recipient animals and which were present in the recipients as a result of prior skin sensitization. In other studies, Asherson et a[. observed that the suppressor B cells are not only associated with the unresponsive states we have mentioned but also with responsive states, e.g. responsiveness in animals receiving topical applications of contactant 3. O n e interpretation of this data is that, after oral exposure to c o n t a c t a n t , suppressor B cells are generated early in the response and in large enough numbers to prevent any observable i m m u n e response at all, whereas after topical application of contactant the suppressor B cells occur late in the response and in lower numbers, so that an i m m u n e response does

develop but is eventually shut off. An alternative explanation, based on the fact that suppressor B cells occur during states of both responsiveness and unresponsiveness, is that the suppressor B cells are not involved in oral tolerance to contactants; in this case, the suppressor T cells or other suppressor components (as discussed below) might be important factors. Assuming that suppressor B cells do play a role in oral unresponsiveness, several mechanisms of suppression are possible. In the first place, it is well known that antibody to stimulating antigen may cause immunosuppression4, so suppressor B cells might act by producing antibodies that have suppressor effects. There is some support for this explanation in the observation that mice orally immunized with sheep red blood cells (SRBC) develop serum suppressor factors which, at least in part, react with i m m u n i z i n g antigen. In the relevant studies, mice were given SRBC by intragastric i n t u b a t i o n and cells and serum from such animals were examined for suppressor capabilityL Feeding with SRBC, unlike contactants (mentioned above) or soluble proteins (mentioned below), induced no suppressor cells in the spleen of recipient animals but their serum contained a substance which suppressed the responses of both unfed animals subsequently i m m u n i z e d with SRBC irz ~,i~o and virgin cells cultured with SRBC zr~ vilro. This suppressor capability was antigen-specific and nonH-2 restricted; in addition, it was absorbed by staphylococcal protein A or ~Sephadex' coated with anti-mouse-lg, whereas absorption with i m m u n i z i n g antigen (SRBC) was succ'essful only some of the time 5. A. B. +660

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158 I n a n o t h e r study, o n zl,-e,ilro responses, the suppressor substance was shown to be an IgG a n t i b o d y specific for S R B C and to be p r e d o m i n a n t l y iGgf'. The soluble suppressor substance was not an IgA antibody as suggested in earlier' studies conducted by some of the same invest!gatorsL Suppressor B cells induced during oral immunization may also mediate suppression through the production of antibodies with specificity for antigen receptors on immune cells (anti-idiotypic antibodies). Such antibodies can induce negative feedback effects. However, the data in support of such a mechanism are very scanty and consist mainly of the observation that prototype antibody responses can be negatively regulated by anti-idiotypic antibodies s. In the study mentioned above 5, the serum suppressor factor associated with unresponsiveness to oral administra' t i o n of S R B C could not always be a b s o r b e d out with immunizing antigen, raising the possibility that at least part of the activity was due to anti-idiotypic antibody. A third possibility is that suppressor B cells induced during oral immunization cause unresponsiveness by the secondary induction of suppressor T cells. B-cell blasts can induce suppression through activation of inducer T cells which, in turn, activate suppressor T cells ~). In addition, antigen-coated cells, p r e s u m a b l y including antigen-coated B cells, can activate a network of suppressor T cells, first those with specificity for antigen, then those with specificity for idiotypC °. W h e t h e r or not such mechanisms operate in the intestinal tract is not yet known.

Suppression of oral re.;pon.resby T cells Oral i m m u n i z a t i o n with protein antigens is the best d o c u m e n t e d i n s t a n c e in which a n t i g e n - s p e c i f i c DONOR FED

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suppressor T cells are observed after antigen feeding. Typically animals are fed antigen and at some later point cells from their Peyer's patches or spleen are transferred to a syngeneic recipient that is concomitantly or sequentially i m m u n i z e d with the same antigen via a parenteral route (see inset to Fig. 3). The response of the recipient is then c o m p a r e d with that of animals not receiving cells or receiving cells from unfed donor animals. In such studies first the Peyer's patches and later the spleens of fed animals are found to contain T cells (but not B cells), which can specifically suppress the response of recipient animals ~'. This suppression includes IgG and lgE antibody responses as well as antigeninduced T-cell proliferation and delayed skin reactions. In oral unresponsiveness induced by the soluble protein ovalbumin (OVA) no circulating suppressor substance accompanies the suppressor T cells: serum from such animals did not suppress a n t i - O V A responses when given to recipients which were subsequently immunized parenterally. In addition, although OVA-fed animals and recipients of spleen ceils from OVA-fed animals did not support secondary antiO V A responses, irradiated OVA-fed animals could support such secondary responses% This indicates that the suppression in this system is radiosensitive and therefore cannot be a n t i b o d y - m e d i a t e d . There is recent evidence that orally induced suppressor T cells may operate (at least in part) through an antigen-specific factor '3 released during culture of spleen cells fi'om SRBC-fed mice. Animals treated with anti-lymphocyte serum (ALS) did not produce the suppressor factor, indicating that the factor was Tcell dependent if not produced by T cells. Interestingly, a helper factor with a different molecular weight and separable from the suppressor factor on a size RESPONSES IN RECIPIENT SPLEEN

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In this experiment ceils are transferred between donor and recipient animals in the manner illustrated in the insert. Bars represent plaque-forming cell response (PFC's) measured in spleen of recipient animals 3 days after transfer of Peyer's patch T cells obtained from saline or OVA-fed donor animals. Recipients of T cells from OVA fed animals have a decreased IgG anti-OVA response and an increased IgA anti-OVA response. Thus, as in the polyclonal system (Fig. 2) the regulation of IgG and lgA are independent.

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immunologyto@, August 7981 basis was also found in spleen-cell supernatants from fed animals; this factor was obtained from cells from ALS-treated mice but not adult thymectomized mice. It should be added that in unfractionated supernatants suppression dominated over help since the net effect was suppression. One additional point of interest is that suppressor T cells and not suppressor factors appear to mediate the suppression of delayed-type responses after oral exposure to SRBC; this is true in spite of the fact that the same antigen given orally, as indicated above, evokes a serum suppressor factor, but not suppressor cells ~4. Thus, the humoral and delayed-type hypersensitivity (DTH) unresponsiveness following oral SRBC exposure are mediated by different mechanisms which appear to be independent of one another.

Oral unresponsiveness mediated by clone inhibition Although various suppressor cells a n d / o r factors have been shown to be capable of mediating oral unresponsiveness, one must be cautious about concluding that they are actually responsible for the unresponsive state. This caveat has greater validity as a result of the recent work by Miller el al. 15 who studied the unresponsiveness induced by injecting mice with hapten-modified autologous lymphoid cells (e.g. DNP-spleen cells). It preceded the appearance of suppressor T cells and persisted long after they could no longer be demonstrated by adoptive transfer. The term 'clonal inhibition' has been given to the mechanism governing the state of unresponsiveness; it applies either to the actual elimination of cells bearing antigen-specific receptors for the antigen/tolerogen ('clonal deletion') or to the inactivation of such cells without actual cell destruction ('clonal blockade'). That clonal inhibition is involved in oral unresponsiveness is inherent in the studies of R i c h m a n et al:, who found that suppressor T cells, which could be easily demonstrated 1 week after O V A feeding, could not be demonstrated 4 weeks after O V A feeding even though the mice were still unresponsive at this time when challenged with O V A in complete Freund's adjuvant (CFA) 16. Additional work is necessary to define the importance of clonal inhibition in oral unresponsiveness and to determine whether or not the apparent absence of suppressor cells during unresponsiveness is real or due to our inability to detect them with currently available methods~ Role of non-spee~c suppression in oral unresponsiveness Until now we have focussed on antigen-specific suppression induced by antigens presented from the intestinal lumen. Recently, however; it has become clear that lumenal material, particularly bacterial endotoxin, induces a good deal of non-specific (or

159 more accurately, polyspecific) suppression in both mucosal and systemic lymphoid tissues. As for the cellular mechanism of this non-specific suppression, it has been shown that conventional mice have greater suppressor T-cell activity than do germfree mice relative to the proliferative response induced by mitogens (LPS) and the antibody response induced by antigen (TNP-LPS) 17. Furthermore, LPS-unresponsive C 3 H / H e J mice have greater helper T-cell activity than do LPS-responsive C 3 H / H e N mice relative to the antibody response induced by oral administration of TNP-SRBC. These data imply that LPS and other gut constituents induce T-cell-mediated suppression of mucosal immuiae responses. Non-specific suppressor mechanisms are also seen in the rat, but in this species the responsible cell is a macrophage. It has been known for some time that normal (conventional) rat spleen contains a strong non-specific suppressor activity due to adherent cells with macrophage characteristics. Mattingly et al. have found that such suppressor activity is not present in the spleens of germfree rats and that the generation of suppressor macrophages is dependent on the presence of a normal bacterial flora in the intestine 18. Nonspecific suppressor cells may also be pre.sent in the mucosal lymphoid tissues of the rabbit ~ and in the h u m a n lamina propria 2°, so this p h e n o m e n o n p r o b a b l y represents an i m p o r t a n t host defense mechanism. H o w non-specific suppression relates to the antigen-specific unresponsiveness seen after antigen feeding is unknown. It is clear, however, that the mucosat lymphoid tissues operate in an extremely complex milieu compared with lymphoid tissues at other sites, and that a variety of non-specific factors are likely to affect the responsiveness or nonresponsiveness to specific enteric antigens. Role of the liver in oral unresJ2onsiveness Over a decade ago experiments done by Cantor and Dumont strongly implicated the liver as an important factor in oral tolerance. They found that portacaval shunting in dogs, i.e. diversion of blood emanating from the intestinal tract away from the liver, abolished the unresponsiveness that normally follows ingestion of dinitrochlorobenzene 2~. These findings suggest that antigens going to the liver via the portal system induce specific unresponsiveness, but the mechanism of such unresponsiveness is unknown. Because antigens going to the liver would necessarily involve liver macrophages (Kupffer cells), it is likely that liver macrophages are critical to the induction of suppressor responses. Recent techniques for Kupffer cell isolation have shown that purified Kupffer cells pulsed with antigen in vitro are fully capable of inducing T-cell proliferation 22. However, whether or not the T cells so induced are more likely to be suppressor.T cells remains unknown and awaits further work.

160

Some generalizalion,~ concerning ora! imresponsiveness Clearly we are .just beginning to understand oral unresponsiveness but the various studies reviewed above suggest several tentative conclusions. Firstly, the unresponsiveness which follows the feeding of any given antigen may involve more than one mechanism. Consequently, the presence of one does not exclude the involvement of others. Secondly, different mechanisms of unresponsiveness may exist simultaneously for B-cell-mediated (humoral) and T-cell-mediated (delayed-type hypersensitivity) responses. Thirdly, there appear to be many similarities between the unresponsiveness which follows antigen feeding and the more familiar unresponsiveness which follows parenteral injection of antigen. For example, unresponsiveness after the feeding of h u m a n gammaglobulin (HGG) and the injection of it both have the same kinetics and both affect the same cell compartments 23. In addition, the suppressive serum factor which appears after the feeding of SRBC to mice is indistinguishable from the factor induced by injection of mice with SRBC hemolysate 24. Despite these similarities one must be mindful of the fact that oral administration of antigen can frequently lead to unresponsiveness even if systemic administration of the same antigen leads to stimulation of an immune response; this implies that differences in regulatory mechanisms in the mucosal and systemic immune systems do exist.

Oral immunization Thus far in this discussion, we have considered only the mechanisms of unresponsiveness which follows antigen feeding. However, antigen feeding can also result in immunization, both after natural infection with a variety of viruses and bacteria and after the feeding of experimental antigens - many of them the same antigens which can induce unresponsiveness, as discussed above. Presentation of antigen by the enteric route appears to prime particularly 25 but not exclusively 2" for local mucosal responses of the IgA class. There is, in fact, very little information available on cellular mechanisms involved in oral immunization, although recent work by Pierce and Koster in the cholera toxin system has given us a glimpse into what appears to be a number of complex regulatory circuits 27. They have shown that intraperitoneal administration of cholera toxoid in CFA 2 weeks before oral administration of cholera toxin leads to an augmented mucosal anti-cholera toxoid response, whereas cholera toxoid given intrapetitoneally without adjuvant induces suppression of the response to the same oral dose of cholera toxin. Furthermore, prior ir~jection of cholera toxoid intravenously, or subcutaneously (with or without adjuvant), leads to suppression of the mucosal response after antigen feeding. This last experiment is, in effect, a mirror image of the experiments detailed above i n ' w h i c h

imm~mologlrl(~dar,,,b~g~c~t19~1 antigen feeding prior to systemic immunization led to suppression of the systemic immune response. Finally, whereas toxoid in CFA given i.p. 14 days before the oral immunizing doses enhances the local immune response, the same antigen given 1 14 days before the oral response is suppressive. These studies show that the route and timing of antigen are quite critical in determining the precise set of regulatory cells which will eventually participate in a mucosal immune response.

Class specific regulation of mucosal immune responses From the studies reviewed above it is far from clear when oral antigen will induce a positive immune response (immunization) or a negative response (tolerance, unresponsiveness). Some insight into this problem may be gained from the observation that oral unresponsiveness applies, for the most part, to systemic immune responses involving lgG and IgM antibodies, whereas oral immunization applies mainly to mucosal immune responses, involving IgA antibodies. This raises the possibility that there is classspecific regulation which allows for the concomitant suppression of the systemic lgG and IgM response and enhancement of the mucosal lgA response. Recent data have shown that IgA responses are governed by regulatory mechanisms distinct from those governing IgG and lgM responses2S. 2'). The relevant studies involve both a polyclonal mitogenactivated indicator system and an antigen-activated indicator system. In the former case, it was shown first that LPS induces synthesis of IgM, lgG and lgA in both routine spleen and Peyer's patch cultures as indicated by the presence of secreted imnmnoglobulin in culture supernatants (measured by radioimmunoassay). It was then shown that con A-pulsed spleen T cells (i.e. T cells with enhanced suppressor activity) added to spleen-cell cultures containing LPS caused suppression of immunoglobulin synthesis involving all immunoglobulin classes including IgA, whereas con A-pulsed Peyer's patch T cells added to Peyer's patch cultures (also containing LPS) caused suppression of IgM and igG synthesis but enhancement of IgA synthesis (Fig. 2). Con A-pulsed cells from Peyer's patches, but not spleen, apparently had a differential etTect on immunoglobulin synthesis, in that the 'mix' of regulatory cells induced by con A in Peyer's patches had a net helper effect for lgA and a net suppressor effect for IgM and lgG. This differential effect was not due to the fact that B cells in Peyer's patches and B cells in spleen respond difterently to regulatory influences because the same effect, i.e. enhanced lgA synthesis, was obtained if spleen was used as the B-cell source. Finally, the enhanced lgA response seen with Peyer's patch con A-treated T cells is not due to increased helper" activity for all Ig classes, the latter being masked by the greater sensitivity of

immu~olos;y Loda),, Augur! 19~;1

IgM a n d lgG B cells to suppressor signals, because when con A-pulsed T cells are a d d e d to cultures under c o n d i t i o n s in which h e l p e r T-cell effects are maximized, both Peyer's patch T cells and spleen T cells have an equal capacity to help IgM, lgG and IgA synthesis. In all, these data indicate that IgA regulatory T-cell activity varies independently of IgM and IgG regulatory T-cell activity; they are thus most compatible with the concept that separate classspecific regulatory cells exist for IgA as distinct from other immunoglobulin classes. A similar conclusion was reached with an antigenspecific system 2'). In this case, Peyer's patch cells from OVA-fed mice were transferred to syngeneic recipients immunized with O V A at the time of transfer. Recipient response was assessed from the n u m b e r of antigen-specific plaque-forming cells in spleen. As in previous studies of this kind, recipients of Peyer's patch cells from the fed mice had lower lgG a n t i - O V A responses than had recipients of cells from saline-fed donor animals but at the same time they had higher IgA a n t i - O V A responses (Fig. 3). Thus, as in the case of the polyclonal response, antigen-specific IgG suppression was a c c o m p a n i e d by antigen-specific IgA enhancement. In an elaboration of this experiment the donor cell population was depleted of all T cells (treatment with a n t i - T h y 1.2 + complement) or only suppressor T cells (treatment with anti-Lyt 1.2 + complement). In the former case suppression of IgG and enhancement of IgA in the recipient were both eliminated, whereas in the l a t t e r l g G a n t i - O V A s u p p r e s s i o n was eliminated but |gA a n t i - O V A enhancement was maintained. Thus IgA help and IgG suppression again a p p e a r to be independent events, an independence which is best explained by the presence of class-specific regulatory T cells. In these studies, lgA class-specific regulatory T cells were defined on the basis of functional studies. This cell must be identified by morphological (marker) studies. It may be found in the population of T cells which b e a r m e m b r a n e l g A - F c but not I g G - F c receptors -~. This T-cell population could recognize lgA via its Fc receptor and therefore respond in a positive or negative regulatory tashion toward B cells producing lgA antibody. However, recent studies indicate that there is no simple relationship between the distribution of IgA-Fc receptor-bearing cells in various tissues and IgA synthesis in such tissues ~. Thus, the role of this cell population in IgA regulation awaits functional studies of purified IgA-Fc receptorbearing T-cell populations. Role of clas.~-.speci/ic regulalory T cells in lhe pkenomerm of oral re.spoz~siver~ess and non-responsivene.~s.

T h e identification of a separate regulatory system governing IgA responses has certain implications for our understanding of oral responsiveness and non-

161

responsiveness. In the first place, since IgA responses are highly T-cell dependent, a class-specific regulatory T cell for IgA adds a new element to the mix of factors that must be considered in the investigation of the mucosal immune responses. In this regard, it is possible that the intestinal environment leads tO the induction of a cadre of class-specific regulatory T cells vital to the expansion of the lgA B-cell system. According to this view, IgA-bearing B cells can p r o b a b l y differentiate from B-cell precursors bearing I g M and IgD in the absence of T cells but they must await a p p r o p r i a t e T-cell signals before their final level of expansion is determined. T h e mucosal environment is thus operating through regulatory T cells in the generation of IgA responses, In the second place, the existence of separate classspecific regulatory systems for each of the Ig classes leads to the prediction that any of a variety of responses can occur, depending on the way in which the regulatory cells were stimulated. As indicated above, under some circumstances, oral stimulation m a y lead to IgG suppression (systemic suppression) associated with lgA enhancement (mucosal enhancement). U n d e r other conditions, both IgG and IgA responses m a y be e n h a n c e d , or b o t h m a y be suppressed. The challenge for further research is to define the conditions and cellular interactions which produce these various outcomes. References I Chase, M. W. (1946) Proc. Soc. t'2vp. Biol. Med. 61,257-259 2 Asherson, G. l.., Zembala, M., Perera, M. A. C. C., Mayhew, B., Thomas, W. R. (1977) (.?ll. Immurml. 33, 145-155 3 Asherson, G. L., Perera, M. A. C. C., Thomas, W. R., Zembala, M. (1979) in Immuzlolr~gy r~fBreast Milk (Ogra, P. L. and Dayton, D. eds) pp. 19-36, Raven Press, New York 4 Weigle, W. O. (1975) Adv. Immunol. 21, 87-lli 5 Kagnoff, M. F. (1978) (,?[l. hmmmol. 40, 186-203 6 Chalon, M. P., Milne, R. W., Vaerman, J. P. (1979) Eur. J. lmmunol. 9, 747-751 7 AndrE, C., Heremans, J. F., Vaerman, J. P., Cambiaso, C. L. (1975),7. Exp. Med. 142, 1509-1519 8 Sy, M. S., Moorhead, J. W., Claman, tl. N. (1979)J. lmmurm[. 123, 2593-2598 9 L'Age-Stehr, J., Teichmann, H., Gershon, R. K, Cantor, H. (1980) Eur. J. Immuzml. 10, 21-26 10 Sy, M. S., Brown, A. R., Benacerraf, B., Greene, M. I. (1980) J. Exp. Med. 151,896-909 11 Richman, L. K., Chiller, J. M., Brown, W. R., Hanson, 1). G., Vaz, N. M. (1978) J. lmmurwl. 121, 2429-2434 12 Hanson, D. G., Vaz, N. M., Maia, L. C. S., Lynch, .J.M. (1979) J. [mmunol. 123, 2337-2343 13 Mattingly, ,J. A., Waksman, B. H. (1978),7. Immunol. 121, 1878-1883 14 Kagnoff,J.F.(1978)J. lmmurml.120,1509 1513 I5 Miller, S. D., Sy, M.-S., Claman, H. N. (1977) Eur. J. Immzmd. 7, 165-170 16 Richman, L. K. (1979) in lmmur~dog3~ cJ Breas! Milk (Ogra, P. L. and Dayton, I). eds) pp. 49-59, Raven Press, New York 17 McGhee, J. R., Kiyono, H., Michalek, S. M., Babb, J. L., Rosenstreich, I). L., Mergenhagen, S. E. (1980)J. bnmunol. 124, 1603-1611 18 Mattingly, J. A., Eardley, l). D., Kemp,.J. l)., Gershon, R. K.

immemo/og O, todr(y, A:Lg:~.sl 1~)~1

162

(1979) ..7. Immured. 122, 787-790 19 Reid, R. H. (19'79) Oaslroel~lerot%rea76, 1225 20 Clancy, R., Pucci, A. (1978) Adv. Ev/). Med. 13lot. 107, 575-582 21 Cantor, H. M., I)umont, A. E. (1967) .Vatlere (Lomhm) 215, 744-745 22 Riehman, L. K., Klingenstein, R. J., Richman, J. A., Strober, W., Berzofsky,J. (1980) ,7. Immlmd. 123, 2602-2608 23 Vives, J., Parks, D. E., Weigle, W. O. (1980) ,7. Imm~mol. 125, 1811-1816 24 Kagnoff, M. F. (1980) (:a~Lroe~lerologia79, 54-61 25 Crabbe, P. A., Nash, 1). R., Bazin, H., Eyssen, H., Heremans,

J. F. (1969) J. Evl2.Med. 130, 723-744 26 Fujita, K., Finkelstein, R. A. (1972) J. l@~cl. Dis. 125,647-655 27 Pierce, N. F., Koster, F. T. (1980) J. lmrrmnol. 124, 307-311 28 Elson, C. O., Heck, J. A., Strober, W. (1979).7. E.vp. Med. 149, 632-643 29 Richman, L. K., Graefl, A. S., Yarchoan, R., Strober, W. (1981) (submitted), 30 Strober, W., Hague, N. E., Lum, L. (2-., Henkart, P. (1978) J. Immune/. 127, 2440-2445 31 Arnaud-Battandier, F., Hague, N. E., Lure, L. G., Elson, C. O., Strober, W. (1980) (,'ell. Immanol. 55, 106-113

The delayed hypersensitivity T cell and its interaction with other T cells A. A. Nash and P. G. H. Gell Department of Pathology, University of Cambridge, Cambridge, U.K. In this review T<)ny JV cells, not at the I region. (ii) Lymphokines are always induced by antigen under the influence of specifically sensitized '1;~H cells,

though not always exclusively from them 2. The most conveniently, or at least most frequently measured lymphokine is macrophage inhibition factor (MIF). This factor, defined in terms of its test, has been used as a definitive criterion for the occurrence of a I)H reaction; however, release of M I F is not always immunologically mediated ~. Possibly other lymphokines might be more suitable; but the ' l y m p h o k i n e s ' grade into the group of inflammatory factors which are released as the result of almost any mild t r a u m a or stimulation of lymphoid cells, and are unlikely ever to supply a really tight criterion. (iii) The proliferation assay ([3H]thymidine uptake in the presence of antigen) has been uncritically accepted as a firm indication of I)H without any demonstration that antigen stimulation of other T cells (TH, Tcr and even Ts) m a y not on occasion lead to cell proliferation. Moreover, we have found (Nash, unpublished observation) that in mice tolerized to herpes virus (see b e l o w ) a brisk proliferation response occurs in vitro without any macroscopic evidence in the intact animal of the presence of DH. It might perhaps be argued that the in-e:itro response gives a truer picture of the presence of D t t cells than the in-e~ivoskin test (supposing the latter to be interfered with by such factors as defects in m a c r o p h a g e presentation of antigen, suppressor cells, a n t i - i n f l a m m a t o r y prostaglandins etc.), hampering the production or release of mitogenic factor in viva but not in vitro. However this is yet to be proved, and would in any case be of little clinical value. It is possible that DH would best be defined, or