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Avian Leukocytic Cytokines
Avian Leukocytic Cytokines KIRK C. KLASING Department of Avian Sciences, University of California, Davis, California 95616 ABSTRACT Leukocytic cytokines are produced by cells of the immune system and are prominent regulators of the immune response and in some cases various systemic responses. Leukocytic cytokines are released during immune responses and may act in autocrine, paracrine, or endocrine manners. Although over a dozen avian leukocytic cytokines have been described based on functional activities, characterization at the molecular level is not well developed. Two exceptions are 1) myelomonocytic growth factor, a colony-stimulating factor-like cytokine required for the growth and differentiation of hematopoietic precursor cells, particularly myelomonocytic cells; and 2) the avian transforming growth factor-/3 (TGF-J3) family of cytokines, which modulate wound healing, bone metabolism, and cellular differentiation. Cytokines with bioactivities similar to mammalian interleukin (IL)-l, IL-2, IL-6, and interferon-7 have been at least partially purified. Cytokines with bioactivities similar to mammalian IL-8, colony-stimulating factor, and tumor necrosis factor-a have been reported but are not well characterized at the molecular level. With a few exceptions, including TGF-|8 and thymulin, highly purified leukocytic cytokines of mammalian origin have diminished or no specific activity in avian assay systems. The chicken IL-1 receptor has been cloned and the predicted amino acid sequence shares 60% homology with the human IL-1 receptor. A component of the chicken IL-2 receptor has been partially purified but little is known about other avian leukocytic cytokine receptors. Potential applications of leukocytic cytokines in poultry production originate from their regulation of a variety of functions such as disease resistance, wound healing, bone accretion, nutrient partitioning, appetite, growth, and reproduction. (Key words: aves, cytokines, interleukins, immune response, vaccination) 1994 Poultry Science 73:1035-1043
GENERAL CYTOKINE NOMENCLATURE AND PHYSIOLOGY The proliferation, differentiation, and metabolism of avian cells are regulated by soluble mediators including hormones, growth factors, cytokines, prostaglandins, leukotrienes, and thromboxanes. The best characterized are the hormones that originate from the endocrine system and thus have an endocrine gland as their origin. Cytokines are peptide mediators not produced by a discreet endocrine gland, but rather by widely dispersed cells and tissues. Characterization of cytokines has
Received for publication July 25, 1993. Accepted for publication March 10, 1994.
been difficult due to their diffuse origin and often localized actions. Nevertheless, cytokines have been subjected to intense investigation because they are implicated in the etiology of a variety of processes underlying homeostasis and disease, including regulation of the immune response. Leukocytic cytokines are produced by cells of the immune system and are prominent regulators of the immune response and in some cases various systemic responses. The large family of leukocytic cytokines are frequently subdivided in several ways. The most common subdivision is by the cell of origin, including lymphokines and monokines, produced by lymphocytes and monocytes, respectively. Subdivisions based on functional
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criteria include interleukin (IL), colonystimulating factor (CSF), and chemokine, which describe interlymphocyte communication, induction of differentiation and maturation of leukocytic precursors, and chemoattractive functions, respectively. All of the nomenclature schemes adopted to date suffer from multiple cell sources of most cytokines and extensive redundancy and pleiotropy of cytokine actions. For example, IL-1 is typically classified as either a monokine or an IL, indicating that it is a cytokine produced by macrophages that acts in the communication between lymphocytes. Although the main source of IL-1 is macrophages, this IL also produced by many other cell types. Interleukin-1 has actions on a myriad of cell types other than lymphocytes, including granulocytes, fibroblasts, endothelial cells, osteoblasts, osteoclasts, hepatocytes, neurons, muscle cells, adipocytes, and leukocyte progenitor cells. Depending on the target cell, the actions of IL-1 include the induction of proliferation, cell death, anabolism, catabolism, activation, deactivation, chemotaxis, migration inhibition, differentiation, or dedifferentiation. It is clear that development of a specific and accurate nomenclature for cytokines is difficult. Contributing to the confusion is the historical naming of cytokines by members of different disciplines based on various functions. For example, IL-1 was previously named "lymphocyte activating factor", "B cell activating factor", and "T cell replacement factor" by immunologists; "endogenous pyrogen" and "hepatocyte activating factor" by pathologists interested in the acute phase response; "catabolin", "osteoclast activating factor", and "leukocyte activating factor" by physiologists interested in metabolism; and "hemopoietin 1" by hematologists. The numerous isolations, characterizations, and molecular clonings of what is now called IL-1 by many different groups in disparate disciplines demonstrates the tremendous pleiotropy of its actions. There is also considerable redundancy among the leukocytic cytokines. For example, IL-1, IL-2, IL-4, IL-6, tumor necrosis factor-a (TNF-a), RANTES (regulated upon activation, normal T cell expressed and secreted factor), and several CSF all
induce the proliferation of T cells. The molecular cloning of most of the leukocytic cytokines from human or murine cells has helped reduce the confusion and permits more consistent nomenclature and exact characterization. In aves, molecular characterization is incomplete and the identification of leukocytic cytokines is usually based on mammalian equivalents with similar bioactivities. Leukocytic cytokines are released during immune responses and may act in autocrine, paracrine, or endocrine manners. High levels of specific cytokine activities can be seen in culture supernatant of freshly isolated leukocytes induced with a mitogen or immunogen in vitro. Some cytokine activities can also be observed in the blood from chicks challenged with pathogens or immunogens. For example, coccidiosis increases plasma concentrations of TNF-a activity, CSF activity, and interferon (Byrnes et al., 1993b), and Salmonella typhimuriutn lipopolysaccharide increases the plasma concentrations of IL-1 activity in chicks (Klasing et al, 1987). Presumably, some cytokines are released at the site of challenge in sufficient quantities to make their way into the general circulation, where they may act on distant tissues to coordinate recruitment of new leukocytes and the acute phase response. Monokines in particular have systemic, hormone-like roles, whereas lymphokines generally act locally. AVIAN EQUIVALENTS OF MAMMALIAN LEUKOCYTIC CYTOKINES Culture supernatants from stimulated avian leukocytes possess many bioactivities similar to those described in mammals. A list of bioactivities described in the literature using avian cells as the source of, or target for, cytokines is presented in Table 1. Several reviews on avian lymphokines and monokines have been published recently and serve as valuable references for IL-1, IL-2, interferon, TNF-a, and several undefined leukocytic cytokines (Klasing, 1991; Schat, 1991; Lillehoj et al, 1992). Characterization of most of the avian cytokines for which functional activities
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TABLE 1. Avian leukocytic cytokines that have mammalian equivalents based on bioactivity1 Cytokine2
Source
IL-1
Bombara and Taylor, 1991 Klasing and Peng, 1990 Hayari et al, 1982 Byrnes et al, 1993a cSplenocytes chickens T corticosterone Brezinschek et al, 1990 cPBL, spleen cLymphocyte mitogen Fredericksen and Sharma, 1987 Vainio et al, 1986 Meyers et al, 1992 rHuman clntestine anion secretion Chang et al, 1990 cMacrophage cHepatocyte t fibrinogen synthesis Amrani et al, 1986 cFibroblast cHepatocyte t fibronectin synthesis Samad et al, 1993 rHuman cHepatocyte t fibrinogen synthesis Amrani, 1990 cHDH cMyeloblasts t colony formation Leutz et al, 1988, 1989 cSerum cMarrow t colony formation Byrnes et al, 1993b cFibroblast cHeterophils chemotaxis Barker et al, 1993 cFibroblast cDNA expression Gonneville et al, 1991 rHuman cHeterophils chemotaxis Rot, 1991 cLymphocyte cPBL i migration Joshi and Glick, 1990 cSpleen antiviral Dijkmans et al, 1990 cSpleen Fredericksen and Sharma, 1987 cSpleen antiviral cEmbryo rHuman cFibroblasts mitogen Sieweke et al, 1990 Jakowlew et al, 1992 cFibroblasts cDNA expression rHuman cFibroblasts mitogen Sieweke et al, 1990 Qureshi et al, 1990 cytolysis cMacrophage RP9 Klasing and Peng, 1990 I LPL cMacrophage cAdipocyte Byrnes et al, 1993a T cytolysis cMacrophage mL929 Gendron et al, 1991 cDNA expression cNeurons Barger et al, 1991 maturation cThymus cMarrow Chang and Marsh, 1993 maturation cThymus cT cell
IL-2 IL-3 IL-63 CSF4 IL-8 MIF5 IFN PDF TGF-/3 TNF-a
TH Thymulin
cMacrophage
Target
Activity
cThymocyte
co-mitogen
Reference
Abbreviations: c = chicken; CSF = colony-stimulating factor; h = human; IL = interleukin; INF = interferon; LPL = lipoprotein lipase; m = murine; MIF = migration inhibitory factor; PBL = peripheral blood lymphocyte; PDF = platelet derived growth factor; TGF = transforming growth factor; TH = thymic hormone; TNF = tumor necrosis factor; 2 Names are those given to the human cytokine that was defined by the bioactivity demonstrated in an avian system. 3 Referred to as hepatocyte stimulating factor by the investigators, but activity is similar to what is now called IL-6 in mammals. 4 Referred to as myelomonocytic growth factor by the investigators, but activity is typical of a CSF in mammals. 5 Referred to as lymphocyte inhibitory factors by the investigators, but activity is similar to that of MIF in mammals.
have been described (Table 1) at the molecular level is not well developed with a few notable exceptions (Table 2). The best characterized of the avian leukocytic cytokines is myelomonocytic growth factor (MGF), a CSF-like cytokine required for the growth and differentiation of hematopoietic precursor cells, particularly myelomonocytic cells. Bacterial lipopolysaccharide-stimulated HD11 macrophages release MGF in multiple forms as deter-
mined by molecular weight. The different forms are generated by the posttranslational glycosylation of a 24-kDa polypeptide precursor (Leutz et al, 1988). Both the MGF cDNA and the MGF gene have been cloned, revealing that the MGF gene, but not its promoter, is related to the mammalian granulocyte CSF and IL-6 genes (Leutz et al, 1989; Sterneck et al, 1992). The nucleotide sequences for the avian transforming growth factor-/3 (TGF-/3) fa-
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KLASING TABLE 2. Molecular characterization of avian leukocytic cytokines1
Cytokine2
Protein size
cDNA Cloned
Homology
Reference
MGF
24 kDa
Yes
41% with hIL-6
Leutz et al, 1988, 1989; Sterneck et al, 1992
TGF-& IL-1
Yes No
ATH
112 amino acids 16 to 21.5 kDa 53 kDa 10, 20.5 kDa 14, 26 kDa 17.5 to 25, 36 to 39 kDa 25 to 40 kDa 20.5 kDa 20 to 29 kDa 17, 36 kDa 22-30 kDa 29 to 52, 15 to 29 kDa 15 to 16 kDa
No
-80% with ha-parvalbumin5
Thymulin
9 amino acids6
No
-100% with hThymulin
IL-2
IL-63 IFN
MIF4
56% with hG-CSF 79% with hTGF-/32
No
No No
Jakowlew et al., 1988 Brezinschek et al., 1990 Klasing and Peng, 1990 Schnetzler et al, 1983 Fredericksen and Sharma, 1987 Meyers et al, 1992 Amrani et al, 1986 Pusztai et al, 1986 Krempien et al, 1985 Fredericksen and Sharma, 1987 Dijkmans et al, 1990 Joshi and Glick, 1990
No
Barger et al, 1991 Brewer et al, 1989, 1991 Marsh, 1993
Abbreviations: ATH = avian thymic hormone; c = chicken; CSF = colony-stimulating factor; h = human; IL = interleukin; INF = interferon; MGF = myelomonocytic growth factor; MIF = migration inhibitory factor; TGF = transforming growth factor; TNF = tumor necrosis factor. 2 Except where noted, names are those given to the human cytokines that were defined by the bioactivity demonstrated in an avian system. 3 Referred to as hepatocyte stimulating factor by the investigators, but activity is similar to what is now called IL-6 in mammals. ^Referred to as lymphocyte inhibitory factors by the investigators, but activity is similar to that of MIF in mammals. 5 Homology is based on amino acid sequences. 6 Deduced from mammalian sequence and comparison with bioactivity of mammalian preparation in avian systems.
mily of cytokines have been determined and include at least two isoforms (TGF-184 and TGF-/35), which have not been found in mammals (Jackolew et al, 1988, 1992). Functions of TGF-/3 demonstrated in avian systems are mostly related to cellular differentiation, wound repair, and bone metabolism and growth. For example, in aves, TGF-/3 stimulates fibroblast (Sieweke et al, 1990) and chondrocyte proliferation (Rosier et al, 1989). In mammals, TGF-/3 has a variety of immunoregulatory functions, including induction of monokine release, chemotaxis of monocytes and neutrophils, and stimulation of IgA secretion from B cells.
Characterization of avian cytokines by different groups often result in discrepancies in either the size or charge determined (Table 2). Presumably, this is due to glycosylation differences, aggregation with other proteins, or the formation of dimers and trimers under some conditions. Alternately, there are often several distinct cytokines that demonstrate a bioactivity used to monitor purification. Different investigators may have isolated different cytokines and given them the same name. Protein sequencing and cloning of the genes must be done to resolve these possibilities. There is considerable confusion regarding the species specificity between avian
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and mammalian cytokines. Highly purified cytokines of human and murine origin are commercially available and in some instances are active in avian cell systems, although with a considerable loss in specific activity. Human recombinant IL-6 stimulates the synthesis of the acute phase proteins, fibrinogen and fibronectin, in chick hepatocytes in a dose-dependent manner (Amrani, 1990; Samad et ah, 1993). Human recombinant TNF-a has activity on avian cells as indicated by angiogenesis in the developing chick chorioallantoic membrane (Leibovich et ah, 1987) and increased fatty acid synthesis in chick hepatic cells (Butterwith and Griffin, 1989). Chick fibroblasts proliferate in response to porcine TGF-|8 (Jakowlew et ah, 1992), human recombinant TGF-a, human recombinant platelet-derived growth factor, and human recombinant epidermal growth factor (Sieweke et ah, 1990). Mammalian thymulin is active on avian thymocytes and bone marrow cells (Chang and Marsh, 1993). In contrast, rIL-1 does not stimulate chicken thymocytes to increase their rate of division in the presence of submitogenic levels of phytohemagglutinin (PHA) (Klasing and Peng, 1987). Similarly, mammalian IL-2 does not induce the proliferation of chicken lymphocytes (Schauenstein et ah, 1987). There is strict species specificity for the interferons, IL-3, IL-4, and the CSF between humans and mice, suggesting that activity of these mammalian cytokines on avian cells would be negligible given the greater evolutionary distance. Going the other direction, crude or partially purified preparations of avian cytokines have been tested for activity in mammalian assay systems. For example, purified chicken MGF is devoid of activity in murine colony-stimulating assays and human liver assays (Leutz et ah, 1989), and partially purified chicken IL-1 shows only weak activity at inducing mitogenesis in murine thymocytes (Klasing and Peng, 1987) or cytotoxicity in murine LM cells (Klasing and Peng, 1990).
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characterized and cloned (see review by Taga and Kishimoto, 1993), and many of the second messengers have been determined. The receptors have been assigned to several families based on structural similarities. Many receptors require a separate receptor-associated protein in order to bind ligand with high affinity or transmit signals to the cytoplasm. The sharing of the same receptor-associated protein and signal transduction pathways between unrelated cytokines gives insight into their redundancy in bioactivities. The chicken IL-1 receptor has been cloned and the predicted amino acid sequence shares 60% homology with the human IL-1 type-1 receptor (Guida et ah, 1992). The intracellular domain, which is responsible for signal transduction, has 79 and 80% homology with the same region in the human receptor and the Toll receptor of Drosophila melanogaster, respectively. The extracellular region of the receptor has a typical Ig-like structure typical of mammalian IL-1 receptors. Although the mechanism of signal transduction of avian and mammalian IL-1 is controversial, Bombara and Taylor (1991) demonstrated that maximal IL-1 release from chicken HD11 macrophages occurs through mechanisms requiring both protein kinase and calmodulin-dependent protein kinase and that elevated levels of cyclic adenosine 5'-monophosphate enhances IL-1 release. Hala et ah (1986) and Schauenstein et ah (1988) characterized a monoclonal antibody that reacts with a 48- to 50-kDa cell surface antigen on chicken T lymphocytes. This protein corresponds to the mammalian CD25, light chain of mammalian IL-2 (Fedecka-Bruner et ah, 1991). The time course of expression of the surface antigen following the activation of T lymphocytes is similar to that seen for the mammalian IL-2 receptor. The IL-2-dependent proliferation of mitogen-stimulated lymphocytes is competitively inhibited by the surface antigen, further suggesting that it is a component of the IL-2 receptor. Similarly, Lee and Tempelis (1991) have characterized a monoclonal antibody that reacts RECEPTORS AND INHIBITORS strongly with lymphoblasts but not resting spleen cells, and inhibits the IL-2 activity The receptors for most of the mam- of conditioned medium from concanavalin malian leukocytic cytokines have been
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A (Con A)-activated spleen cells. The monoclonal antibody was used to immunoprecipitate a surface protein from Con A-activated lymphocytes with a molecular weight of about 110 kDa (Lee and Tempelis, 1992). This receptor may be analogous to the y subunit of the IL-2 receptor. The ligand binding (extracellular) regions of IL-1, IL-2, IL-4, IL-6, IL-7, IL-9, TNF-a, granulocyte-CSF, and interferon-7 receptors have been detected in culture supernatants of stimulated mammalian cells or in blood plasma of infected mammals (Taga and Kishimoto, 1993). In some cases these soluble receptors are released from the cell membrane by proteolysis. In other cases they are secreted from the cell due to alternative splicing of the mRNA. In most cases the soluble receptor inhibits the biological activity of their respective ligands, providing an additional opportunity for regulation of the immune response. In the case of IL-1, another mechanism for downregulation is the release of an antagonist that binds to the receptor but does not elicit signal transduction; thus blocking the binding of authentic IL-la and IL-1/3. It is generally thought that cells produce soluble receptors for IL-1, TNF-a, and the IL-1 receptor antagonist in order to blunt the local cytotoxic effects of high levels of IL-1 and TNF-a. Several avian cytokine inhibitors have been described in the literature. Davila et al. (1987), isolated a 61-kDa peptide from chicken blood serum that inhibits lectininduced splenocyte proliferation and IL-2 synthesis. These characteristics suggest that the factor may be a soluble IL-1 receptor or receptor antagonists. Schaefer et al. (1985) found that Con A-stimulated peripheral blood monocytes produce a factor that inhibits the mitogenesis of peripheral blood lymphocytes. This suppressor activity is opposed by stimulatory factors, possibly IL-2, suggesting that the suppressor factor inhibits either IL-1 or IL2 action. Similarly, splenic macrophagelike cells stimulated by infectious bursal disease virus produce a soluble factor that markedly reduces Con-A-induced mitogenesis of splenic lymphocytes and release of IL-2-like activity (Sharma and
Fredericksen, 1987). Klasing (unpublished data) has examined the supernatants from Escherichia coli lipopolysaccharidestimulated peritoneal macrophages for activity that blocks IL-1 induced comitogenesis of broiler thymic cells (Figure 1). Peaks of IL-1-inhibiting activity were observed at -65 and 30 kDa, along with a very low molecular weight inhibitor, possibly a prostaglandin. The size of the larger IL-1 inhibitor is similar to the circulating inhibitor described by Davila et al (1987) and the human soluble IL-1 receptor. APPLICATIONS
Potential applications of leukocytic cytokines originate from their regulatory roles in a variety of processes that are fundamental to poultry production. Their roles in disease resistance include regulation of leukocyte maturation and recruitment, regulation of the intensity of cellu-
.0
E 55
0
5
10
15
20
25
30
35
40
Fraction number
FIGURE 1. Sephadex-elicited peritoneal macrophages were stimulated with Escherichia coli lipopolysaccharide and supernatants were concentrated 50x and subjected to molecular sizing chromatography and fractions were tested for inhibition of thymocyte mitogenesis driven by 4 /*g/mL phytohemagglutinin (PHA)-P and partially purified chicken interleukin (IL)-l (Klasing and Peng, 1990). Stimulation index is expressed as the ratio of 3 H-thymidine incorporation into thymocytes in the presence of the column fraction, PHA-P, and IL-1 to that with PHA-P alone.
SYMPOSIUM: CURRENT ADVANCES IN AVIAN IMMUNOLOGY
lar, humoral, and inflammatory immune responses, and determination of the type of immune response that predominates following a challenge (i.e., tolerance, cellular immunity, humoral immunity, or inflammation). Many of these same cytokines also regulate other physiological systems including wound healing, bone accretion, nutrient partitioning, appetite, growth, and reproduction (Baxter and Ross, 1991; Klasing and Johnstone, 1991). Initial optimism that marked improvements in immunocompetence and disease resistance could be gained by continuous supplementation of a leukocytic cytokine or amplifying its endogenous expression by transgenic manipulations has proven to be unwarranted. Leukocytic cytokines, such as IL-1, IL-2, IL-6, and TNF-a that might augment immunocompetence, impair growth and reproduction (Klasing and Johnstone, 1991). Nevertheless, understanding the biology of leukocytic cytokines may permit the use of leukocytic cytokines, their agonists, or antagonists to optimize disease resistance through vaccination. For example, in mammals IL-1 is important in initiating and sustaining cellular and humoral immune responses. In broilers, partially purified preparations can act as an adjuvant to boost the antibody response to a vaccination with SRBC (Klasing, 1987). This information may permit optimization of commercial adjuvants and allow better management of vaccination programs. Mammalian cytokines responsible for directing the type of immune response that follows recognition of disease organisms have been defined. Interferon y, IL-4, IL-10, and IL-12 interact to drive naive T helper (Th) cells toward T hl or T^ subsets, initiating cell-mediated or humoral immunity, respectively (Scott, 1993). Modulation of these cytokines may allow the direction of the immune response to a vaccine toward the type that offers the best protection against a specific pathogen. Leukocytic cytokines are peptides that are expensive to manufacture and administer. Relative to individually valuable large animals such as cattle or horses, poultry are not generally considered a target species for administration of cytokines for commercial benefit due to
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their low individual cost. However, manipulation of the release or action of leukocytic cytokines may have a variety of applications in modern poultry production. Cook et al. (1993) demonstrated that conjugated isomers of linoleic acid ameliorates the monokine-mediated reduction in appetite and growth rate that follows a repeated challenge with E. coli lipopolysaccharide. Linoleic acid is a precursor for the synthesis of prostaglandins, including prostaglandin E2, which mediate many of the catabolic and anorectic effects of IL-1 and TNF-a (Meydani, 1992). The selective blocking of the systemic catabolic actions of IL-1 and other cytokines that mediate the acute phase response without interfering with local immunoregulatory actions of the cytokine may have commercial utility in poultry production.
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Purificaaffinity chromatography and sodium tion of avian T cell growth factor and immune dodecyisulfate-polyacrylamide gel electrophoreinterferon using gel filtration high resolution sis. J. Interferon Res. 5:209. chromatography. Page 145 in: Avian Immunology. W. T. Weber and D. L. Ewert, ed. Alan R. Lee, T., and C. H. Tempelis, 1991. Characterization of Liss, New York, NY. a receptor on activated chicken T cells. Dev. Comp. Immunol. 15:329-339. Gendron, R. L., F. P. Nestel, and W. S. Lapp, 1991. Expression of tumor necrosis factor alpha in the Lee, T., and C. H. Tempelis, 1992. Possible 110 kDa developing nervous system. Int. J. Neurosci. 60: receptor for Interleukin 2 in the chicken. Dev. 129-136. Comp. Immunol. 16:463-472. Gonneville, L., T. J. Martins, and P. A. Bedard, 1991. Leibovich, S. Joseph, P. J. Polverini, H. M. Shepard, Complex expression pattern of the CEF-4 D. M. Wiseman, V. Shively, and N. Nuseir, 1987. cytokine in transformed and mitogenically Macrophage-induced angiogenesis is mediated stimulated cells. Oncogene 6:1825-1833. by tumour necrosis factor-a. Nature 329: 630-632. Guida, S., A. Heguy, and M. Melli, 1992. The chicken IL-1 receptor: differential evolution of the Leutz, A., H. Beug, C. Walter, and T. Graf, 1988. cytoplasmic and extracellular domains. Gene Hematopoietic growth factor glycosylation. J. 111:239-243. Biol. Chem. 263:3905-3911. Hala, K., K. Schauenstein, M. Neu, G. Kromer, H. Leutz, A., K. Damm, E. Sterneck, E. Kowenz, S. Ness, R. Frank, H. Gausepohl, Y. E. Pan, J. Smart, M. Wolf, G. Bock, and G. Wick, 1986. A monoclonal Hayman, and T. Graf, 1989. Molecular cloning antibody reacting with a membrane deterof the chicken myelomonocytic growth factor minant expressed on activated chicken T lym-
SYMPOSIUM: CURRENT ADVANCES IN AVIAN IMMUNOLOGY (cMGF) reveals relationship to interleukin 6 and granulocyte colony stimulating factor. EMBO J. 8:175-181. Lillehoj, H. S., B. Kaspers, M. C. Jenkins, and E. P. Lillehoj, 1992. Avian interferon and interleukin2. A review by comparison with mammalian homologues. Poultry Sci. Rev. 4:67-85. Marsh, J. A., 1993. The humoral activity of the avian thymic microenvironment. Poultry Sci. 72: 1294-1300. Meydani, S. N., 1992. Modulation of cytokine production by dietary polyunsaturated fatty acids. PSEBM 200:189-193. Myers, T. J., H. S. Lillehoj, and R. H. Fetterer, 1992. Partial purification and characterization of chicken interleukin-2. Vet. Immunol. Immunopathol. 34:94-114. Pusztai, R., B. Tarodi, and I. Beladi, 1986. Production and characterization of interferon induced in chicken leukocytes by Concanavalin A. Acta Virol. 30:131-136. Qureshi, M. A., L. Miller, H. S. Lillehoj, and M. D. Ficken, 1990. Establishment and characterization of a chicken mononuclear cell line. Vet. Immunol. Immunopathol. 26:237-250. Rot, A., 1991. Chemotactic potency of recombinant human neutrophil attractant/activation protein1 (interleukin-8) for polymorphonuclear leukocytes of different species. Cytokine 3:21-27. Rosier, R. N., R. J. O'Keefe, I. D. Crabb, and J. E. Puzas, 1989. Transforming growth factor beta: an autocrine regulator of chondrocytes. Connect. Tissue Res. 20:295-301. Samad, F., G. Bergtrom, H. Eissa, and D. L. Amrani, 1993. Stimulation of chick hepatocyte fibronectin production by fibroblast-conditioned medium is due to interleukin 6. Biochim. Biophys. Acta 1181:207-213. Schaefer, A. E., A. R. Scafuri, T. L. Fredericksen, and D. G. Gilmour, 1985. Strong suppression by monocytes of T cell mitogenesis in chicken
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peripheral blood leukocytes. J. Immunol. 135: 1652-1660. Schat, K. A., 1991. T-cell immunity: mechanisms and soluble mediators. Pages 35-50 in: Avian Cellular Immunology. J. M. Sharma, ed. CRC Press, St. Paul, MN. Schauenstein, K., G. Kromer, R. Fassler, and G. Wick, 1987. Implications of IL-2 in normal and disturbed immune functions in the chicken. Dev. Comp. Immunol. 11:69-77. Schauenstein, K., G. Kromer, K. Hala, G. Bock, and G. Wick, 1988. Chicken-activated-T-lymphocyteantigen (CATLA) recognized by monoclonal antibody INN-CH 16 represents the IL-2 receptor. Dev. Comp. Immunol. 12:823-831. Schnetzler, M., A. Oommen, J. S. Nowak, and R. M. Franklin, 1983. Characterization of chicken T cell growth factor. Eur. J. Immunol. 13:560-568. Scott, P., 1993. IL-12: initiation cytokine for cellmediated immunity. Science 260:496-497. Sharma, J. M., and T. L. Fredericksen, 1987. Mechanism of T cell immunosuppression by infectious bursal disease virus of chickens. Pages 283-294 in: Avian Immunology. W. T. Weber and D. L. Ewert, ed. Alan R. Liss, New York, NY. Sieweke, M. H., N. L. Thompson, M. B. Sporn, and M. J. Bissell, 1990. Mediation of wound-related rous sarcoma virus tumorigenesis by TGF-/J. Science 248:1656-1660. Sterneck, E., C. Blattner, T. Graff, and A. Leutz, 1992. Structure of the chicken myelomonocytic growth factor gene and specific activation of its promoter in avian myelomonocytic cells by protein kinases. Mol. Cell. Biol. 12:1728-1735. Taga, T., and T. Kishimoto, 1993. Cytokine receptors and signal transduction. FASEB J. 7:3387-3396. Vainio, O., M.J.H. Ratcliffe, and T. Leanderson, 1986. Chicken T-cell growth factor: Use in the generation of a long-term cultured T-cell line and biochemical characterization. Scand. J. Immunol. 23:135-142.
GENERAL CYTOKINE NOMENCLATURE AND PHYSIOLOGY The proliferation, differentiation, and metabolism of avian cells are regulated by soluble mediators including hormones, growth factors, cytokines, prostaglandins, leukotrienes, and thromboxanes. The best characterized are the hormones that originate from the endocrine system and thus have an endocrine gland as their origin. Cytokines are peptide mediators not produced by a discreet endocrine gland, but rather by widely dispersed cells and tissues. Characterization of cytokines has
Received for publication July 25, 1993. Accepted for publication March 10, 1994.
been difficult due to their diffuse origin and often localized actions. Nevertheless, cytokines have been subjected to intense investigation because they are implicated in the etiology of a variety of processes underlying homeostasis and disease, including regulation of the immune response. Leukocytic cytokines are produced by cells of the immune system and are prominent regulators of the immune response and in some cases various systemic responses. The large family of leukocytic cytokines are frequently subdivided in several ways. The most common subdivision is by the cell of origin, including lymphokines and monokines, produced by lymphocytes and monocytes, respectively. Subdivisions based on functional
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criteria include interleukin (IL), colonystimulating factor (CSF), and chemokine, which describe interlymphocyte communication, induction of differentiation and maturation of leukocytic precursors, and chemoattractive functions, respectively. All of the nomenclature schemes adopted to date suffer from multiple cell sources of most cytokines and extensive redundancy and pleiotropy of cytokine actions. For example, IL-1 is typically classified as either a monokine or an IL, indicating that it is a cytokine produced by macrophages that acts in the communication between lymphocytes. Although the main source of IL-1 is macrophages, this IL also produced by many other cell types. Interleukin-1 has actions on a myriad of cell types other than lymphocytes, including granulocytes, fibroblasts, endothelial cells, osteoblasts, osteoclasts, hepatocytes, neurons, muscle cells, adipocytes, and leukocyte progenitor cells. Depending on the target cell, the actions of IL-1 include the induction of proliferation, cell death, anabolism, catabolism, activation, deactivation, chemotaxis, migration inhibition, differentiation, or dedifferentiation. It is clear that development of a specific and accurate nomenclature for cytokines is difficult. Contributing to the confusion is the historical naming of cytokines by members of different disciplines based on various functions. For example, IL-1 was previously named "lymphocyte activating factor", "B cell activating factor", and "T cell replacement factor" by immunologists; "endogenous pyrogen" and "hepatocyte activating factor" by pathologists interested in the acute phase response; "catabolin", "osteoclast activating factor", and "leukocyte activating factor" by physiologists interested in metabolism; and "hemopoietin 1" by hematologists. The numerous isolations, characterizations, and molecular clonings of what is now called IL-1 by many different groups in disparate disciplines demonstrates the tremendous pleiotropy of its actions. There is also considerable redundancy among the leukocytic cytokines. For example, IL-1, IL-2, IL-4, IL-6, tumor necrosis factor-a (TNF-a), RANTES (regulated upon activation, normal T cell expressed and secreted factor), and several CSF all
induce the proliferation of T cells. The molecular cloning of most of the leukocytic cytokines from human or murine cells has helped reduce the confusion and permits more consistent nomenclature and exact characterization. In aves, molecular characterization is incomplete and the identification of leukocytic cytokines is usually based on mammalian equivalents with similar bioactivities. Leukocytic cytokines are released during immune responses and may act in autocrine, paracrine, or endocrine manners. High levels of specific cytokine activities can be seen in culture supernatant of freshly isolated leukocytes induced with a mitogen or immunogen in vitro. Some cytokine activities can also be observed in the blood from chicks challenged with pathogens or immunogens. For example, coccidiosis increases plasma concentrations of TNF-a activity, CSF activity, and interferon (Byrnes et al., 1993b), and Salmonella typhimuriutn lipopolysaccharide increases the plasma concentrations of IL-1 activity in chicks (Klasing et al, 1987). Presumably, some cytokines are released at the site of challenge in sufficient quantities to make their way into the general circulation, where they may act on distant tissues to coordinate recruitment of new leukocytes and the acute phase response. Monokines in particular have systemic, hormone-like roles, whereas lymphokines generally act locally. AVIAN EQUIVALENTS OF MAMMALIAN LEUKOCYTIC CYTOKINES Culture supernatants from stimulated avian leukocytes possess many bioactivities similar to those described in mammals. A list of bioactivities described in the literature using avian cells as the source of, or target for, cytokines is presented in Table 1. Several reviews on avian lymphokines and monokines have been published recently and serve as valuable references for IL-1, IL-2, interferon, TNF-a, and several undefined leukocytic cytokines (Klasing, 1991; Schat, 1991; Lillehoj et al, 1992). Characterization of most of the avian cytokines for which functional activities
SYMPOSIUM: CURRENT ADVANCES IN AVIAN IMMUNOLOGY
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TABLE 1. Avian leukocytic cytokines that have mammalian equivalents based on bioactivity1 Cytokine2
Source
IL-1
Bombara and Taylor, 1991 Klasing and Peng, 1990 Hayari et al, 1982 Byrnes et al, 1993a cSplenocytes chickens T corticosterone Brezinschek et al, 1990 cPBL, spleen cLymphocyte mitogen Fredericksen and Sharma, 1987 Vainio et al, 1986 Meyers et al, 1992 rHuman clntestine anion secretion Chang et al, 1990 cMacrophage cHepatocyte t fibrinogen synthesis Amrani et al, 1986 cFibroblast cHepatocyte t fibronectin synthesis Samad et al, 1993 rHuman cHepatocyte t fibrinogen synthesis Amrani, 1990 cHDH cMyeloblasts t colony formation Leutz et al, 1988, 1989 cSerum cMarrow t colony formation Byrnes et al, 1993b cFibroblast cHeterophils chemotaxis Barker et al, 1993 cFibroblast cDNA expression Gonneville et al, 1991 rHuman cHeterophils chemotaxis Rot, 1991 cLymphocyte cPBL i migration Joshi and Glick, 1990 cSpleen antiviral Dijkmans et al, 1990 cSpleen Fredericksen and Sharma, 1987 cSpleen antiviral cEmbryo rHuman cFibroblasts mitogen Sieweke et al, 1990 Jakowlew et al, 1992 cFibroblasts cDNA expression rHuman cFibroblasts mitogen Sieweke et al, 1990 Qureshi et al, 1990 cytolysis cMacrophage RP9 Klasing and Peng, 1990 I LPL cMacrophage cAdipocyte Byrnes et al, 1993a T cytolysis cMacrophage mL929 Gendron et al, 1991 cDNA expression cNeurons Barger et al, 1991 maturation cThymus cMarrow Chang and Marsh, 1993 maturation cThymus cT cell
IL-2 IL-3 IL-63 CSF4 IL-8 MIF5 IFN PDF TGF-/3 TNF-a
TH Thymulin
cMacrophage
Target
Activity
cThymocyte
co-mitogen
Reference
Abbreviations: c = chicken; CSF = colony-stimulating factor; h = human; IL = interleukin; INF = interferon; LPL = lipoprotein lipase; m = murine; MIF = migration inhibitory factor; PBL = peripheral blood lymphocyte; PDF = platelet derived growth factor; TGF = transforming growth factor; TH = thymic hormone; TNF = tumor necrosis factor; 2 Names are those given to the human cytokine that was defined by the bioactivity demonstrated in an avian system. 3 Referred to as hepatocyte stimulating factor by the investigators, but activity is similar to what is now called IL-6 in mammals. 4 Referred to as myelomonocytic growth factor by the investigators, but activity is typical of a CSF in mammals. 5 Referred to as lymphocyte inhibitory factors by the investigators, but activity is similar to that of MIF in mammals.
have been described (Table 1) at the molecular level is not well developed with a few notable exceptions (Table 2). The best characterized of the avian leukocytic cytokines is myelomonocytic growth factor (MGF), a CSF-like cytokine required for the growth and differentiation of hematopoietic precursor cells, particularly myelomonocytic cells. Bacterial lipopolysaccharide-stimulated HD11 macrophages release MGF in multiple forms as deter-
mined by molecular weight. The different forms are generated by the posttranslational glycosylation of a 24-kDa polypeptide precursor (Leutz et al, 1988). Both the MGF cDNA and the MGF gene have been cloned, revealing that the MGF gene, but not its promoter, is related to the mammalian granulocyte CSF and IL-6 genes (Leutz et al, 1989; Sterneck et al, 1992). The nucleotide sequences for the avian transforming growth factor-/3 (TGF-/3) fa-
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KLASING TABLE 2. Molecular characterization of avian leukocytic cytokines1
Cytokine2
Protein size
cDNA Cloned
Homology
Reference
MGF
24 kDa
Yes
41% with hIL-6
Leutz et al, 1988, 1989; Sterneck et al, 1992
TGF-& IL-1
Yes No
ATH
112 amino acids 16 to 21.5 kDa 53 kDa 10, 20.5 kDa 14, 26 kDa 17.5 to 25, 36 to 39 kDa 25 to 40 kDa 20.5 kDa 20 to 29 kDa 17, 36 kDa 22-30 kDa 29 to 52, 15 to 29 kDa 15 to 16 kDa
No
-80% with ha-parvalbumin5
Thymulin
9 amino acids6
No
-100% with hThymulin
IL-2
IL-63 IFN
MIF4
56% with hG-CSF 79% with hTGF-/32
No
No No
Jakowlew et al., 1988 Brezinschek et al., 1990 Klasing and Peng, 1990 Schnetzler et al, 1983 Fredericksen and Sharma, 1987 Meyers et al, 1992 Amrani et al, 1986 Pusztai et al, 1986 Krempien et al, 1985 Fredericksen and Sharma, 1987 Dijkmans et al, 1990 Joshi and Glick, 1990
No
Barger et al, 1991 Brewer et al, 1989, 1991 Marsh, 1993
Abbreviations: ATH = avian thymic hormone; c = chicken; CSF = colony-stimulating factor; h = human; IL = interleukin; INF = interferon; MGF = myelomonocytic growth factor; MIF = migration inhibitory factor; TGF = transforming growth factor; TNF = tumor necrosis factor. 2 Except where noted, names are those given to the human cytokines that were defined by the bioactivity demonstrated in an avian system. 3 Referred to as hepatocyte stimulating factor by the investigators, but activity is similar to what is now called IL-6 in mammals. ^Referred to as lymphocyte inhibitory factors by the investigators, but activity is similar to that of MIF in mammals. 5 Homology is based on amino acid sequences. 6 Deduced from mammalian sequence and comparison with bioactivity of mammalian preparation in avian systems.
mily of cytokines have been determined and include at least two isoforms (TGF-184 and TGF-/35), which have not been found in mammals (Jackolew et al, 1988, 1992). Functions of TGF-/3 demonstrated in avian systems are mostly related to cellular differentiation, wound repair, and bone metabolism and growth. For example, in aves, TGF-/3 stimulates fibroblast (Sieweke et al, 1990) and chondrocyte proliferation (Rosier et al, 1989). In mammals, TGF-/3 has a variety of immunoregulatory functions, including induction of monokine release, chemotaxis of monocytes and neutrophils, and stimulation of IgA secretion from B cells.
Characterization of avian cytokines by different groups often result in discrepancies in either the size or charge determined (Table 2). Presumably, this is due to glycosylation differences, aggregation with other proteins, or the formation of dimers and trimers under some conditions. Alternately, there are often several distinct cytokines that demonstrate a bioactivity used to monitor purification. Different investigators may have isolated different cytokines and given them the same name. Protein sequencing and cloning of the genes must be done to resolve these possibilities. There is considerable confusion regarding the species specificity between avian
SYMPOSIUM: CURRENT ADVANCES IN AVIAN IMMUNOLOGY
and mammalian cytokines. Highly purified cytokines of human and murine origin are commercially available and in some instances are active in avian cell systems, although with a considerable loss in specific activity. Human recombinant IL-6 stimulates the synthesis of the acute phase proteins, fibrinogen and fibronectin, in chick hepatocytes in a dose-dependent manner (Amrani, 1990; Samad et ah, 1993). Human recombinant TNF-a has activity on avian cells as indicated by angiogenesis in the developing chick chorioallantoic membrane (Leibovich et ah, 1987) and increased fatty acid synthesis in chick hepatic cells (Butterwith and Griffin, 1989). Chick fibroblasts proliferate in response to porcine TGF-|8 (Jakowlew et ah, 1992), human recombinant TGF-a, human recombinant platelet-derived growth factor, and human recombinant epidermal growth factor (Sieweke et ah, 1990). Mammalian thymulin is active on avian thymocytes and bone marrow cells (Chang and Marsh, 1993). In contrast, rIL-1 does not stimulate chicken thymocytes to increase their rate of division in the presence of submitogenic levels of phytohemagglutinin (PHA) (Klasing and Peng, 1987). Similarly, mammalian IL-2 does not induce the proliferation of chicken lymphocytes (Schauenstein et ah, 1987). There is strict species specificity for the interferons, IL-3, IL-4, and the CSF between humans and mice, suggesting that activity of these mammalian cytokines on avian cells would be negligible given the greater evolutionary distance. Going the other direction, crude or partially purified preparations of avian cytokines have been tested for activity in mammalian assay systems. For example, purified chicken MGF is devoid of activity in murine colony-stimulating assays and human liver assays (Leutz et ah, 1989), and partially purified chicken IL-1 shows only weak activity at inducing mitogenesis in murine thymocytes (Klasing and Peng, 1987) or cytotoxicity in murine LM cells (Klasing and Peng, 1990).
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characterized and cloned (see review by Taga and Kishimoto, 1993), and many of the second messengers have been determined. The receptors have been assigned to several families based on structural similarities. Many receptors require a separate receptor-associated protein in order to bind ligand with high affinity or transmit signals to the cytoplasm. The sharing of the same receptor-associated protein and signal transduction pathways between unrelated cytokines gives insight into their redundancy in bioactivities. The chicken IL-1 receptor has been cloned and the predicted amino acid sequence shares 60% homology with the human IL-1 type-1 receptor (Guida et ah, 1992). The intracellular domain, which is responsible for signal transduction, has 79 and 80% homology with the same region in the human receptor and the Toll receptor of Drosophila melanogaster, respectively. The extracellular region of the receptor has a typical Ig-like structure typical of mammalian IL-1 receptors. Although the mechanism of signal transduction of avian and mammalian IL-1 is controversial, Bombara and Taylor (1991) demonstrated that maximal IL-1 release from chicken HD11 macrophages occurs through mechanisms requiring both protein kinase and calmodulin-dependent protein kinase and that elevated levels of cyclic adenosine 5'-monophosphate enhances IL-1 release. Hala et ah (1986) and Schauenstein et ah (1988) characterized a monoclonal antibody that reacts with a 48- to 50-kDa cell surface antigen on chicken T lymphocytes. This protein corresponds to the mammalian CD25, light chain of mammalian IL-2 (Fedecka-Bruner et ah, 1991). The time course of expression of the surface antigen following the activation of T lymphocytes is similar to that seen for the mammalian IL-2 receptor. The IL-2-dependent proliferation of mitogen-stimulated lymphocytes is competitively inhibited by the surface antigen, further suggesting that it is a component of the IL-2 receptor. Similarly, Lee and Tempelis (1991) have characterized a monoclonal antibody that reacts RECEPTORS AND INHIBITORS strongly with lymphoblasts but not resting spleen cells, and inhibits the IL-2 activity The receptors for most of the mam- of conditioned medium from concanavalin malian leukocytic cytokines have been
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KLASING
A (Con A)-activated spleen cells. The monoclonal antibody was used to immunoprecipitate a surface protein from Con A-activated lymphocytes with a molecular weight of about 110 kDa (Lee and Tempelis, 1992). This receptor may be analogous to the y subunit of the IL-2 receptor. The ligand binding (extracellular) regions of IL-1, IL-2, IL-4, IL-6, IL-7, IL-9, TNF-a, granulocyte-CSF, and interferon-7 receptors have been detected in culture supernatants of stimulated mammalian cells or in blood plasma of infected mammals (Taga and Kishimoto, 1993). In some cases these soluble receptors are released from the cell membrane by proteolysis. In other cases they are secreted from the cell due to alternative splicing of the mRNA. In most cases the soluble receptor inhibits the biological activity of their respective ligands, providing an additional opportunity for regulation of the immune response. In the case of IL-1, another mechanism for downregulation is the release of an antagonist that binds to the receptor but does not elicit signal transduction; thus blocking the binding of authentic IL-la and IL-1/3. It is generally thought that cells produce soluble receptors for IL-1, TNF-a, and the IL-1 receptor antagonist in order to blunt the local cytotoxic effects of high levels of IL-1 and TNF-a. Several avian cytokine inhibitors have been described in the literature. Davila et al. (1987), isolated a 61-kDa peptide from chicken blood serum that inhibits lectininduced splenocyte proliferation and IL-2 synthesis. These characteristics suggest that the factor may be a soluble IL-1 receptor or receptor antagonists. Schaefer et al. (1985) found that Con A-stimulated peripheral blood monocytes produce a factor that inhibits the mitogenesis of peripheral blood lymphocytes. This suppressor activity is opposed by stimulatory factors, possibly IL-2, suggesting that the suppressor factor inhibits either IL-1 or IL2 action. Similarly, splenic macrophagelike cells stimulated by infectious bursal disease virus produce a soluble factor that markedly reduces Con-A-induced mitogenesis of splenic lymphocytes and release of IL-2-like activity (Sharma and
Fredericksen, 1987). Klasing (unpublished data) has examined the supernatants from Escherichia coli lipopolysaccharidestimulated peritoneal macrophages for activity that blocks IL-1 induced comitogenesis of broiler thymic cells (Figure 1). Peaks of IL-1-inhibiting activity were observed at -65 and 30 kDa, along with a very low molecular weight inhibitor, possibly a prostaglandin. The size of the larger IL-1 inhibitor is similar to the circulating inhibitor described by Davila et al (1987) and the human soluble IL-1 receptor. APPLICATIONS
Potential applications of leukocytic cytokines originate from their regulatory roles in a variety of processes that are fundamental to poultry production. Their roles in disease resistance include regulation of leukocyte maturation and recruitment, regulation of the intensity of cellu-
.0
E 55
0
5
10
15
20
25
30
35
40
Fraction number
FIGURE 1. Sephadex-elicited peritoneal macrophages were stimulated with Escherichia coli lipopolysaccharide and supernatants were concentrated 50x and subjected to molecular sizing chromatography and fractions were tested for inhibition of thymocyte mitogenesis driven by 4 /*g/mL phytohemagglutinin (PHA)-P and partially purified chicken interleukin (IL)-l (Klasing and Peng, 1990). Stimulation index is expressed as the ratio of 3 H-thymidine incorporation into thymocytes in the presence of the column fraction, PHA-P, and IL-1 to that with PHA-P alone.
SYMPOSIUM: CURRENT ADVANCES IN AVIAN IMMUNOLOGY
lar, humoral, and inflammatory immune responses, and determination of the type of immune response that predominates following a challenge (i.e., tolerance, cellular immunity, humoral immunity, or inflammation). Many of these same cytokines also regulate other physiological systems including wound healing, bone accretion, nutrient partitioning, appetite, growth, and reproduction (Baxter and Ross, 1991; Klasing and Johnstone, 1991). Initial optimism that marked improvements in immunocompetence and disease resistance could be gained by continuous supplementation of a leukocytic cytokine or amplifying its endogenous expression by transgenic manipulations has proven to be unwarranted. Leukocytic cytokines, such as IL-1, IL-2, IL-6, and TNF-a that might augment immunocompetence, impair growth and reproduction (Klasing and Johnstone, 1991). Nevertheless, understanding the biology of leukocytic cytokines may permit the use of leukocytic cytokines, their agonists, or antagonists to optimize disease resistance through vaccination. For example, in mammals IL-1 is important in initiating and sustaining cellular and humoral immune responses. In broilers, partially purified preparations can act as an adjuvant to boost the antibody response to a vaccination with SRBC (Klasing, 1987). This information may permit optimization of commercial adjuvants and allow better management of vaccination programs. Mammalian cytokines responsible for directing the type of immune response that follows recognition of disease organisms have been defined. Interferon y, IL-4, IL-10, and IL-12 interact to drive naive T helper (Th) cells toward T hl or T^ subsets, initiating cell-mediated or humoral immunity, respectively (Scott, 1993). Modulation of these cytokines may allow the direction of the immune response to a vaccine toward the type that offers the best protection against a specific pathogen. Leukocytic cytokines are peptides that are expensive to manufacture and administer. Relative to individually valuable large animals such as cattle or horses, poultry are not generally considered a target species for administration of cytokines for commercial benefit due to
1041
their low individual cost. However, manipulation of the release or action of leukocytic cytokines may have a variety of applications in modern poultry production. Cook et al. (1993) demonstrated that conjugated isomers of linoleic acid ameliorates the monokine-mediated reduction in appetite and growth rate that follows a repeated challenge with E. coli lipopolysaccharide. Linoleic acid is a precursor for the synthesis of prostaglandins, including prostaglandin E2, which mediate many of the catabolic and anorectic effects of IL-1 and TNF-a (Meydani, 1992). The selective blocking of the systemic catabolic actions of IL-1 and other cytokines that mediate the acute phase response without interfering with local immunoregulatory actions of the cytokine may have commercial utility in poultry production.
REFERENCES Amrani, D. L., 1990. Regulation of fibrinogen biosynthesis: glucocorticoid and interleukin-6 control. Blood Coag. Fibrin. 1:443-446. Amrani, D. L., D. Mauzy-Melitz, and M. W. Mosesson, 1986. Effect of hepatocyte-stimulating factor and glucocorticoids on plasma fibronectin levels. Biochem. J. 238:365-371. Barger, B. O., J. L. Pace, F. P. Inman, and W. L. Ragland, 1991. Purification and partial characterization of an avian thymic hormone. Thymus 17:181-197. Barker, K. A., A. Hampe, M. Y. Stoeckle, and H. Hanafusa, 1993. Transformation-associated cytokine 9E3/CEF4 is chemotactic for chicken peripheral blood mononuclear cells. J. Virol. 67: 3528-3533. Baxter, A. R. Ross, 1991. Cytokine Interactions and Their Control. John Wiley & Sons, West Sussex, England. Bombara, C. J., and R. L. Taylor, 1991. Signal transduction events in chicken interleukin-1 production. Poultry Sci. 70:1372-1380. Brewer, J. M., J. Arnold, G. G. Beach, W. L. Ragland, and J. K. Wunderlich, 1991. Comparison of the amino acid sequences of tissue-specific paralbumins from chicken muscle and thymus and possible evolutionary significance. Biochem. Biophys. Res. Commun. 181:226-231. Brewer, J. M., J. K. Wunderlich, D. Kim, M. Y. Carr, G. G. Beach, and W. L. Ragland, 1989. Avian thymic hormone (ATH) is a parvalbumin. Biochem. Biophys. Res. Commun. 160: 1155-1161. Brezinschek, H. P., R. Faessler, H. Klocker, G. Kroemer, R. Sgonc, H. Dietrich, R. Jakober, and G. Wick, 1990. Analysis of the immuneendocrine feedback loop in the avian system and its alteration in chickens with spontaneous
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autoimmune thyroiditis. Eur. J. Immunol. 20: phocytes. Eur. J. Immunol. 16:1331-1336. 2155-2159. Hayari, Y., K. Schauenstein, and A. Globerson, 1982. Butterwith, S. C, and H. D. Griffin, 1989. The effects Avian lymphokines, II: interleukin-1 activity in of macrophage-derived cytokines on lipid mesupernatants of stimulated adherent splenocytes tabolism in chicken (Gallus domesticus) hepatoof chickens. Dev. Comp. Immunol. 6:785-789. cytes and adipocytes. Comp. Biochem. Physiol. Jakowlew, S. B., J. Cubert, D. Danielpour, M. B. 94A:721-724. Sporn, and A. B. Roberts, 1992. Differential Byrnes, S., R. Eaton, and M. Kogut, 1993a. In vitro regulation of the expression of transforming interleukin-1 and tumor necrosis factor-alpha growth factor-/? mRNAs by growth factors and production by macrophages form chickens inretinoic acid in chicken embryo chondrocytes, fected with either Eimeria maxima or Eimeria myocytes, and fibroblasts. J. Cell. Physiol. 150: tenella. Int. J. 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