Molecular cloning of the chicken myelomonocytic growth factor (cMGF) reveals relationship to interleukin 6 and granulocyte colony stimulating factor

Evolution of developmental and comparative immunology in poultry: The regulators and the regulated

Avian has a unique immune system that evolved in response to environmental pressures in all aspects of innate and adaptive immune responses, including localized and circulating lymphocytes, diversity of immunoglobulin repertoire, and various cytokines and chemokines. All of these attributes make birds an indispensable vertebrate model for studying the fundamental immunological concepts and comparative immunology. However, research on the immune system in birds lags far behind that of humans, mice, and other agricultural animal species, and limited immune tools have hindered the adequate application of birds as disease models for mammalian systems. An in-depth understanding of the avian immune system relies on the detailed studies of various regulated and regulatory mediators, such as cell surface antigens, cytokines, and chemokines. Here, we review current knowledge centered on the roles of avian cell surface antigens, cytokines, chemokines, and beyond. Moreover, we provide an update on recent progress in this rapidly developing field of study with respect to the availability of immune reagents that will facilitate the study of regulatory and regulated components of poultry immunity. The new information on avian immunity and available immune tools will benefit avian researchers and evolutionary biologists in conducting fundamental and applied research.

Characterization of Subpopulations of Chicken Mononuclear Phagocytes That Express TIM4 and CSF1R

The phosphatidylserine receptor TIM4, encoded by TIMD4, mediates the phagocytic uptake of apoptotic cells. We applied anti-chicken TIM4 mAbs in combination with CSF1R reporter transgenes to dissect the function of TIM4 in the chick (Gallus gallus). During development in ovo, TIM4 was present on the large majority of macrophages, but expression became more heterogeneous posthatch. Blood monocytes expressed KUL01, class II MHC, and CSF1R-mApple uniformly. Around 50% of monocytes were positive for surface TIM4. They also expressed many other monocyte-specific transcripts at a higher level than TIM4^- monocytes. In liver, highly phagocytic TIM4^hi cells shared many transcripts with mammalian Kupffer cells and were associated with uptake of apoptotic cells. Although they expressed CSF1R mRNA, Kupffer cells did not express the CSF1R-mApple transgene, suggesting that additional CSF1R transcriptional regulatory elements are required by these cells. By contrast, CSF1R-mApple was detected in liver TIM4^lo and TIM4^- cells, which were not phagocytic and were more abundant than Kupffer cells. These cells expressed CSF1R alongside high levels of FLT3, MHCII, XCR1, and other markers associated with conventional dendritic cells in mice. In bursa, TIM4 was present on the cell surface of two populations. Like Kupffer cells, bursal TIM4^hi phagocytes coexpressed many receptors involved in apoptotic cell recognition. TIM4^lo cells appear to be a subpopulation of bursal B cells. In overview, TIM4 is associated with phagocytes that eliminate apoptotic cells in the chick. In the liver, TIM4 and CSF1R reporters distinguished Kupffer cells from an abundant population of dendritic cell-like cells.

Antigen presenting cells in a non-mammalian model system, the chicken

The chicken has a different repertoire of tissues, cells and genes of the immune response compared to mammals, yet generally survives infection with viral, bacterial, protozoal and fungal pathogens, and also worms and ectoparasites, just like mammals. Poultry are also probably the most heavily vaccinated group of farmed animals. Antigen presentation to the adaptive immune response therefore obviously normally occurs efficiently in birds. Although comparatively much is known about macrophages and B cells in the chicken, there is as yet little work on the other, professional, antigen-presenting cells, the dendritic cells (DC). Birds also have at least two other sets of phagocytic cells, heterophils and thrombocytes, which may also have the ability to present antigen. Here we review the current state of knowledge about antigen presenting cells in the chicken, concentrating mainly on recent advances in our knowledge of DC.

Measurement of avian cytokines with real-time RT-PCR following infection with the avian influenza virus

Functional and molecular techniques have both been employed to measure the production of cytokines following influenza infection. Historically, the use of functional or antibody-based techniques was employed in mammalian immunology. In avian immunology, only a few commercial antibodies are available to measure avian cytokines. However, the determination of the genomic sequence of Gallus gallus species has made it possible to measure cytokine induction without monoclonal antibody- or functional-based tests, but rather based on molecular techniques. Although these tests do not measure functionally expressed cytokines, the lack of reagents to identify and quantify avian cytokines makes them critical to extend any measure of cytokine response. Measurement of cytokine induction, based on the design of primers and probes for RT-PCR or real-time RT-PCR for the cytokine mRNA, has become one of the more recent technologies reported to measure avian cytokines. It is important to note that small nucleotide polymorphisms between different lines of birds may result in substandard results when using published primer and probe sequences. This requires empirical testing to ensure adequate results.

Haemopoietic growth factor regulation of protein kinases and genes associated with cell proliferation

Haemopoietic growth factors stimulate a number of common biochemical and molecular events despite the high specificity of individual ligand-receptor interactions. Analysis of three distinct colony-stimulating factors (CSFs), interleukin 3 (IL-3), granulocyte-CSF and granulocyte macrophage-CSF, and the lymphocytotropic growth factor IL-2 revealed remarkably similar distal subcellular biochemical signals, although the mode of initial membrane signal transduction may differ significantly. Both early progenitor cell growth factors, such as IL-3, and late-acting factors, such as CSF-1, stimulate tyrosine and serine/threonine substrate phosphorylations. One substrate (p68) is phosphorylated in response to many CSFs and to IL-2, suggesting that it plays a highly conserved role in the signal transduction processes of many different receptor(s). The proliferative CSFs and IL-2 also stimulate the expression of many of the same genes, including protooncogenes, the ornithine decarboxylase gene, and members of the phylogenetically ancient family of stress response genes. Thus although initial membrane events may differ among the proliferative stimulants, the biochemical and molecular convergence of signalling pathways on highly conserved cellular substrates and on the programme of gene expression is seen.

The avian immune genome – a glass half-full or half-empty?

Although in broad terms the avian immune response is remarkably similar to that of mammals, when one looks at specifics birds have a different repertoire of immune organs, cells and molecules compared to those characterized in mammals. Birds lack organized lymph nodes, yet have the Bursa of Fabricius. Birds lack neutrophils and functional eosinophils, yet have a distinct group of polymorphonuclear granulocytes known as heterophils. Birds also have a different repertoire of cytokines, chemokines, Toll-like receptors, defensins and integrins, as detailed in this review.

Expression of chicken interleukin-2 by turkey herpesvirus increases the immune response against Marek's disease virus but fails to increase protection against virulent challenge

As Marek's disease virus continues to evolve towards greater virulence, more efficacious vaccines will be required in the future. We expressed chicken interleukin-2 (IL-2) from a turkey herpesvirus (HVT) in an attempt to increase the efficacy of HVT as a vaccine against Marek's disease. The recombinant IL-2/HVT was safe for in ovo vaccination, although it replicated less in the birds compared with the parent HVT strain. Expression of IL-2 increased the neutralizing antibody response against HVT but did not increase the protection against virulent Marek's disease virus challenge.

A genomic analysis of chicken cytokines and chemokines

As most mechanisms of adaptive immunity evolved during the divergence of vertebrates, the immune systems of extant vertebrates represent different successful variations on the themes initiated in their earliest common ancestors. The genes involved in elaborating these mechanisms have been subject to exceptional selective pressures in an arms race with highly adaptable pathogens, resulting in highly divergent sequences of orthologous genes and the gain and loss of members of gene families as different species find different solutions to the challenge of infection. Consequently, it has been difficult to transfer to the chicken detailed knowledge of the molecular mechanisms of the mammalian immune system and, thus, to enhance the already significant contribution of chickens toward understanding the evolution of immunity. The availability of the chicken genome sequence provides the opportunity to resolve outstanding questions concerning which molecular components of the immune system are shared between mammals and birds and which represent their unique evolutionary solutions. We have integrated genome data with existing knowledge to make a new comparative census of members of cytokine and chemokine gene families, distinguishing the core set of molecules likely to be common to all higher vertebrates from those particular to these 300 million-year-old lineages. Some differences can be explained by the different architectures of the mammalian and avian immune systems. Chickens lack lymph nodes and also the genes for the lymphotoxins and lymphotoxin receptors. The lack of functional eosinophils correlates with the absence of the eotaxin genes and our previously reported observation that interleukin- 5 (IL-5) is a pseudogene. To summarize, in the chicken genome, we can identify the genes for 23 ILs, 8 type I interferons (IFNs), IFN-gamma, 1 colony-stimulating factor (GM-CSF), 2 of the 3 known transforming growth factors (TGFs), 24 chemokines (1 XCL, 14 CCL, 8 CXCL, and 1 CX3CL), and 10 tumor necrosis factor superfamily (TNFSF) members. Receptor genes present in the genome suggest the likely presence of 2 other ILs, 1 other CSF, and 2 other TNFSF members.

v-Myb represses the transcription of Ets-2

The v-Myb oncogene causes monoblastic leukemia and transforms only myelomonocytic cells in culture. The v-Myb protein is nuclear and binds to specific DNA sequences. To identify genes regulated by v-Myb, we utilized primary cells transformed by a retrovirus encoding a v-Myb-estrogen receptor (ER) fusion protein. The Ets-2 gene was not expressed in v-Myb-ER transformed cells in the presence of estradiol, but was expressed within 4 h after estradiol withdrawal. The expression of Ets-2 also increased dramatically following phorbol ester-induced differentiation of the v-Myb-transformed BM2 cell line. Conversely, CRYP-alpha, encoding a transmembrane tyrosine phosphatase, was expressed in the presence but not the absence of estradiol in v-Myb-ER transformed cells. CRYP-alpha was downregulated during the phorbol ester-induced differentiation of BM2 cells. Although LIM-3 expression was estradiol-inducible in v-Myb-ER transformed monoblasts, LIM-3 was expressed neither in primary yolk sac cells transformed by unfused v-Myb nor in BM2 cells. We conclude that although v-Myb has been intensively studied as a transcriptional activator, v-Myb can repress biologically relevant genes such as Ets-2, which promotes macrophage differentiation. In addition, we have shown that some genes that are regulated by a v-Myb-ER fusion protein may not be relevant to the biological function of the unfused v-Myb protein.

The granulocyte colony-stimulating factors (CSF3s) of fish and chicken

Granulocyte colony-stimulating factor (CSF3) is a glycoprotein cytokine, which influences the hematopoiesis of the phagocytic neutrophils and its precursors and was used extensively in cancer therapy and for the treatment of neutropenia in mammals. However, CSF3 is yet to be identified in nonmammalian species mainly because of its rapid mutation. Here, we report the first CSF3 genes from three teleost fishes: Japanese flounder (Paralichthys olivaceus), fugu (Takifugu rubripes), and green-spotted pufferfish (Tetraodon nigroviridis) and present evidence that the chicken (Gallus gallus) myelomonocytic growth factor is in fact the chicken CSF3 orthologue. We support this by showing significant conservation of the CSF3 genes' structure, domains, regulatory motifs, and synteny across species and by phylogenetic analysis. CSF3 orthologues are indeed evolving rapidly and appears to be undergoing purifying selection in mammals but positive selection in fish and chicken. Furthermore, the paralogous fugu and pufferfish CSF3-1s and CSF3-2s are shown to be the ancestral and duplicate genes, respectively. Finally, we demonstrate that the Japanese flounder CSF3 gene is at least involved in immunity based on its basal expression in immune-related tissues and its upregulation in kidney and peripheral blood leukocytes after in vitro stimulation with lipopolysaccharide and a combination of concanavalin A/phorbol myristate acetate.

HLXB9 activates IL6 in Hodgkin lymphoma cell lines and is regulated by PI3K signalling involving E2F3

Multiple cytokines are secreted by Hodgkin lymphoma (HL) cells, notably interleukin-6 (IL6), which is believed to play a significant pathobiological role in this and certain other tumors. Previous work on prostate carcinoma cells has shown that IL6 expression is activated therein by the homeodomain protein GBX2, which we found to be absent in HL cells. Instead, we observed expression of a closely related gene, HLXB9, albeit restricted to HL cells coexpressing IL6. Treatment of HL cell lines with antisense-oligonucleotides directed against HLXB9, forced expression of recombinant HLXB9, and analysis of reporter gene constructs containing IL6 promoter sequences all confirmed the potential of HLXB9 to drive expression of IL6. Chromosomal rearrangements of the HLXB9 locus at 7q36 were not detected in HL cells unlike AML subsets expressing HLXB9. However, inhibition of certain signal transduction pathways revealed that the phosphatidylinositol 3 kinase (PI3K) pathway contributes to HLXB9 expression. AKT/phospho-AKT analysis revealed constitutively active PI3K signalling in HL cell lines. Downstream analysis of PI3K revealed that E2F3 may mediate activation of HLXB9. Taken together, our data show that the PI3K signalling pathway in HL cells is constitutively activated and promotes HLXB9 expression, probably via E2F3, thereby enhancing malignant expression of IL6.

Profile of chicken cytokines induced by lipopolysaccharide is modulated by dietary alpha-tocopheryl acetate

Previously, we found that 25 to 50 IU/kg of dietary vitamin E (VE) had very different immunoregulatory effects than high VE levels (200 IU/kg), and we hypothesized that this difference was due to different cytokine profiles. Chicks were fed 0, 30, or 200 IU/kg supplemental VE and percentages of CD4+CD8-, CD4-CD8+, CD4+CD8+, and CD4-CD8- lymphocytes, and the ratio of CD4+/CD8+ lymphocytes was determined. The expression of chicken splenic interleukin-1beta (IL-1beta), myelomonocytic growth factor (MGF), interferon (IFN-gamma), and transforming growth factor-beta (TGFbeta) mRNA was determined by reverse transcription (RT)-PCR after intravenous injection of lipopolysaccharide (LPS). Due to a tendency for increased CD4-CD8+ lymphocytes at 30 IU/kg VE (P=0.072), the CD4+/CD8+ ratio was significantly lower for 30 IU/kg VE compared with 0 IU/kg VE (P=0.041). The VE dose of 200 IU/kg decreased the constitutive (prior to LPS) expression of TGFbeta. The LPS caused an increase in IL-1beta, MGF, and IFNgamma expression at all VE concentrations and had no effect on IL-2 and TGFbeta mRNA expression. Dietary VE decreased MGF mRNA (P=0.049) in a dose-dependent manner but had no effect on the expression of other cytokines. The decreased expression of MGF could explain the immunomodulatory effect of VE in inflammation.

Differential cytokine responses following Marek's disease virus infection of chickens differing in resistance to Marek's disease

The production of cytokine mRNAs, in addition to viral DNA, was quantified by real-time quantitative reverse transcription-PCR (RT-PCR) (cytokines) or PCR (virus) in splenocytes during the course of Marek's disease virus (MDV) infection in four inbred chicken lines: two resistant (lines 6(1) and N) and two susceptible (lines 7(2) and P). Virus loads were only different after 10 days postinfection (dpi), increasing in susceptible lines and decreasing in resistant lines. Gamma interferon (IFN-gamma) mRNA was expressed by splenocytes from all infected birds between 3 and 10 dpi, associated with increasing MDV loads. For other cytokines, differences between lines were only seen for interleukin-6 (IL-6) and IL-18, with splenocytes from susceptible birds expressing high levels of both transcripts during the cytolytic phase of infection, whereas splenocytes from resistant birds expressed neither transcript. These results indicate that these two cytokines could play a crucial role in driving immune responses, which in resistant lines maintain MDV latency but in susceptible lines result in lymphomas.

Evolution of interleukin-1beta

All jawed vertebrates possess a complex immune system, which is capable of anticipatory and innate immune responses. Jawless vertebrates possess an equally complex immune system but with no evidence of an anticipatory immune response. From these findings it has been speculated that the initiation and regulation of the immune system within vertebrates will be equally complex, although very little has been done to look at the evolution of cytokine genes, despite well-known biological activities within vertebrates. In recent years, cytokines, which have been well characterised within mammals, have begun to be cloned and sequenced within non-mammalian vertebrates, with the number of cytokine sequences available from primitive vertebrates growing rapidly. The identification of cytokines, which are mammalian homologues, will give a better insight into where immune system communicators arose and may also reveal molecules, which are unique to certain organisms. Work has focussed on interleukin-1 (IL-1), a major mediator of inflammation which initiates and/or increases a wide variety of non-structural, function associated genes that are characteristically expressed during inflammation. Other than mammalian IL-1beta sequences there are now full cDNA sequences and genomic organisations available from bird, amphibian, bony fish and cartilaginous fish, with many of these genes having been obtained using an homology cloning approach. This review considers how the IL-1beta gene has changed through vertebrate evolution and whether its role and regulation are conserved within selected non-mammalian vertebrates.

Antiviral and antitumoral effects of recombinant chicken myelomonocytic growth factor in virally induced lymphoma

Chicken myelomonocytic growth factor (cMGF) is a 27-kDa glycoprotein that stimulates the growth and activation of cells from the monocyte/macrophage lineage. Recombinant cMGF was produced in a prokaryotic (Escherichia coli) expression system and purified via a C-terminal His-tag. Treatment of 2-week-old histocompatible B(13)/B(13) chickens highly susceptible to Marek's disease (MD) with rcMGF (two daily injections of 50 microg rcMGF per chicken) enhanced background and LPS-inducible systemic NO (NO3- + NO2-) responses 3 days later. NO has antiviral activity on Marek's disease virus (MDV), a herpesvirus specifically inducing T cell-lymphomas in chickens. When the very virulent strain of MDV RBI-B was inoculated 3 days after treatment with rcMGF, MDV viremia was significantly inhibited and development of visceral tumors was drastically reduced. Combination of rcMGF with partially protective vaccination using a herpesvirus of turkey (HVT) further reducedtumor burden and significantly delayed mortality, but only in very young birds. In conclusion, rcMGF might be worth considering as a stimulator of innate immune response in chickens, such as activation of macrophages and NO production, and thus be beneficial for its antiviral and antitumoral effects in vaccination against MD lymphoma.

RNA destabilization by the granulocyte colony-stimulating factor stem-loop destabilizing element involves a single stem-loop that promotes deadenylation

Granulocyte colony-stimulating factor (G-CSF) mRNA contains two distinct types of cis-acting mRNA destabilizing elements in the 3'-untranslated region. In addition to several copies of the AU-rich element the G-CSF mRNA also contains a destabilizing region that includes several predicted stem-loop structures. We report here that the destabilizing activity resides in a single stem-loop structure within this region. A consensus sequence for the active structure has been derived by site-directed mutagenesis, revealing that a three-base loop of sequence YAU and unpaired bases either side of the stem contribute to the activity. The helical nature of the stem is essential and the stem must be less than 11 bp in length, but the destabilizing activity is relatively insensitive to the sequence within the helix. The stem-loop increases the rate of mRNA deadenylation, most likely by enhancing the processivity of the deadenylation reaction. A protein that binds the stem-loop, but not an inactive mutant form, has been detected in cytoplasmic lysates.

The emerging role of avian cytokines as immunotherapeutics and vaccine adjuvants

The use of antibiotic feed additives and chemical antimicrobials in food production animals is a double-edged sword. On one hand, it helps to prevent the outbreak of disease and promotes the growth of animals, but on the other hand, concerns are mounting over the emergence of antibiotic-resistant bacteria. As a consequence, some countries have already banned the use of in-feed antibiotics which has resulted in meat producers urgently seeking environmentally friendly alternative methods to control disease. Cytokines are proteins that control the type and extent of an immune response following infection or vaccination. They therefore represent excellent naturally occurring therapeutics. The use of cytokines in poultry has become more feasible with the discovery of a number of avian cytokine genes. Since the immune system of chickens is similar to that of mammals, they offer an attractive model system to study the effectiveness of cytokine therapy in the control of disease in livestock. This review will focus on the recent advances made in avian cytokines, with a particular focus on their assessment as therapeutic agents and vaccine adjuvants.

Protective effect of avian myelomonocytic growth factor in infection with Marek's disease virus

Marek's disease virus (MDV) is a herpesvirus that induces T lymphomas in chickens. The aim of this study was to assess the role of the macrophage activator chicken myelomonocytic growth factor (cMGF) in controlling MDV infection. B13/B13 chickens, which are highly susceptible to MD, were either treated with cMGF delivered via a live fowlpox virus (fp/cMGF) or treated with the parent vector (fp/M3) or were left as untreated controls. Seven days later, when challenged with the very virulent RB-1B strain of MDV, the spleens of chickens treated with fp/cMGF showed increased expression of the inducible nitric oxide synthase (iNOS) gene compared to those of control chickens and fp/M3-treated chickens. Increased iNOS gene expression was also accompanied by greater induction of gamma interferon and macrophage inflammatory protein (K203) gene expression, both possible activators of iNOS. fp/cMGF treatment also increased the number of monocytes and systemic NO production in contrast to fp/M3 treatment. Even though cMGF treatment was unable to prevent death for the chickens, it did prolong their survival time, and viremia and tumor incidence were greatly reduced. In addition, cMGF treatment improved the partial protection induced by vaccination with HVT (herpesvirus isolated from turkeys) against RB-1B, preventing 100% mortality (versus 66% with vaccination alone) and greatly reducing tumor development. Treatment with fp/M3 did not have such effects. These results suggest that cMGF may play multiple roles in protection against MD. First, it may enhance the innate immune response by increasing the number and activity of monocytes and macrophages, resulting in increased NO production. Second, it may enhance the acquired immune response, indicated by its ability to enhance vaccine efficacy.

Cytokines of birds: conserved functions--a largely different look

Targeted disruptions of the mouse genes for cytokines, cytokine receptors, or components of cytokine signaling cascades convincingly revealed the important roles of these molecules in immunologic processes. Cytokines are used at present as drugs to fight chronic microbial infections and cancer in humans, and they are being evaluated as immune response modifiers to improve vaccines. Until recently, only a few avian cytokines have been characterized, and potential applications thus have remained limited to mammals. Classic approaches to identify cytokine genes in birds proved difficult because sequence conservation is generally low. As new technology and high throughput sequencing became available, this situation changed quickly. We review here recent work that led to the identification of genes for the avian homologs of interferon-alpha/beta (IFN-alpha/beta) and IFN-gamma, various interleukins (IL), and several chemokines. From the initial data on the biochemical properties of these molecules, a picture is emerging that shows that avian and mammalian cytokines may perform similar tasks, although their primary structures in most cases are remarkably different.

Divergence of the inflammatory response in two types of chickens

We compared inflammatory responses to lipopolysaccharide (LPS) injection in laying type (Brown Nick) to broiler type (Avian x Avian) chicks. Rectal temperature was measured at 0, 1, 2, 4, 6, 12, and 24h after LPS injection (0, 0.1, 0.3, 0.6, 1, 2.5, or 5mg/kg bw). In layers, rectal temperature increased from 41.31+/-0.19 degrees C to a maximum 42.27+/-0.41 degrees C at 4h after 1mg/kg LPS. Relative to layers, the febrile response in broilers was considerably lower, delayed in onset, and required higher levels of LPS (5mg/kg). Proliferation of spleen cells from un-injected chicks in response to LPS, PHA, and Con A was evaluated in vitro. IFNgamma, TGFbeta(2), MGF and IL-1beta relative to beta-actin mRNA expression were analyzed in spleen cells stimulated with LPS. Splenocytes from layers had a higher proliferative response to LPS (P=0.045), but lower proliferative response to PHA (P=0.004) and Con A (P=0.004) than broilers. Expression of mRNA for MGF, IL-1beta and IFNgamma was lower in broilers than in layers (P<0.001). Reduced production of the pro-inflammatory cytokines in broilers could have resulted from the observed increased production of the immunosuppressive cytokine TGFbeta(2.) These differences in cytokine expression may explain the blunted febrile response in broilers compared to layers. Because the acute phase response of inflammation causes decreased food intake, the blunted inflammatory response of broilers may permit faster growth.

Effects of dietary polyunsaturated fatty acids on in vivo splenic cytokine mRNA expression in layer chicks immunized with Salmonella typhimurium lipopolysaccharide

Effects of dietary polyunsaturated fatty acids (PUFA) on immune responses in poultry have been reported. However, effects on the underlying mechanisms, such as the role of cytokines, have not been documented because the necessary tools were lacking. Recently, primer sets for chicken interleukin (IL)-1beta, IL-2, interferon-gamma (IFN-gamma), myelomonocytic growth factor (MGF), and transforming growth factor (TGF)-beta2 have become available. Therefore, in the present study we first examined the in vivo effects of an inflammatory challenge with Salmonella typhimurium lipopolysaccharide (LPS) on cytokine profiles in growing laying-type chicks. Second, we examined whether dietary fat sources affected the observed cytokine profiles. Two hundred forty chicks were assigned in a 2 x 4 factorial design of treatments, with injection with LPS or saline and dietary fat source as factors. Factors were i.v. injection with S. typhimurium LPS or saline (control) and four dietary fat sources: corn oil, linseed oil, menhaden oil, and tallow. Two hours after injection, birds were killed, and their spleens were removed for RNA extraction. Reverse transcription polymerase chain reactions with primer sets for chicken IL-1beta, IL-2, IFN-gamma, MGF, TGF-beta2, and beta-actin were performed with RNA samples pooled by pen. The expression of cytokine mRNA was expressed relative to the level of beta-actin mRNA. Interleukin-1 (P < 0.001), MGF (P < 0.0001), IL-2 (P < 0.001), and IFN-gamma (P < 0.001) mRNA expressions were enhanced by challenge with LPS. Immunization treatment had no effect on TGF-beta2 or beta-actin expression. Dietary treatment did not affect mRNA expression of IL-1, MGF, IFN-gamma, TGF-beta2, or beta-actin. Interleukin-2 expression in LPS-injected birds that were fed the fish-oil-enriched diet was enhanced (P = 0.05). The present study indicates that in vivo effects of immune challenge on cytokine mRNA expression can be measured in poultry. The observation that mRNA level of IL-2, but not the mRNA levels of IFN-gamma or MGF, is enhanced by dietary fish oil at 2 h suggests that dietary PUFA at this moment initially affected naïve T lymphocytes.

Analysis of chicken mucosal immune response to Eimeria tenella and Eimeria maxima infection by quantitative reverse transcription-PCR

The recent cloning of chicken genes coding for interleukins, chemokines, and other proteins involved in immune regulation and inflammation allowed us to analyze their expression during infection with Eimeria. The expression levels of different genes in jejunal and cecal RNA extracts isolated from uninfected chickens and chickens infected with Eimeria maxima or E. tenella were measured using a precise quantitative reverse transcription-PCR technique. Seven days after E. tenella infection, expression of the proinflammatory cytokine interleukin-1beta (IL-1beta) mRNA was increased 80-fold. Among the chemokines analyzed, the CC chemokines K203 (200-fold) and macrophage inflammatory factor 1beta (MIP-1beta) (80-fold) were strongly upregulated in the infected ceca, but the CXC chemokines IL-8 and K60 were not. However, the CXC chemokines were expressed at very high levels in uninfected cecal extracts. The levels of gamma interferon (IFN-gamma) (300-fold), inducible nitric oxide synthase (iNOS) (200-fold), and myelomonocytic growth factor (MGF) (50-fold) were also highly upregulated during infection with E. tenella, whereas cyclooxygenase 2 showed a more modest (13-fold) increase. The genes upregulated during E. tenella infection were generally also upregulated during E. maxima infection but at a lower magnitude except for those encoding MIP-1beta and MGF. For these two cytokines, no significant change in expression levels was observed after E. maxima infection. CD3+ intraepithelial lymphocytes may participate in the IFN-gamma upregulation observed after infection, since both recruitment and upregulation of the IFN-gamma mRNA level were observed in the infected jejunal mucosa. Moreover, in the chicken macrophage cell line HD-11, CC chemokines, MGF, IL-1beta, and iNOS were inducible by IFN-gamma, suggesting that macrophages may be one of the cell populations involved in the upregulation of these cytokines observed in vivo during infection with Eimeria.

Antagonism between C/EBPbeta and FOG in eosinophil lineage commitment of multipotent hematopoietic progenitors

The commitment of multipotent cells to particular developmental pathways requires specific changes in their transcription factor complement to generate the patterns of gene expression characteristic of specialized cell types. We have studied the role of the GATA cofactor Friend of GATA (FOG) in the differentiation of avian multipotent hematopoietic progenitors. We found that multipotent cells express high levels of FOG mRNA, which were rapidly down-regulated upon their C/EBPbeta-mediated commitment to the eosinophil lineage. Expression of FOG in eosinophils led to a loss of eosinophil markers and the acquisition of a multipotent phenotype, and constitutive expression of FOG in multipotent progenitors blocked activation of eosinophil-specific gene expression by C/EBPbeta. Our results show that FOG is a repressor of the eosinophil lineage, and that C/EBP-mediated down-regulation of FOG is a critical step in eosinophil lineage commitment. Furthermore, our results indicate that maintenance of a multipotent state in hematopoiesis is achieved through cooperation between FOG and GATA-1. We present a model in which C/EBPbeta induces eosinophil differentiation by the coordinate direct activation of eosinophil-specific promoters and the removal of FOG, a promoter of multipotency as well as a repressor of eosinophil gene expression.

Expression of cytokine genes in Marek's disease virus-infected chickens and chicken embryo fibroblast cultures

The role of cytokines in the pathogenesis and immunity of Marek's disease (MD), a herpesvirus-induced T-cell lymphoma in chickens, is poorly understood. Two different experiments were used to examine the potential role of particular cytokines in the pathogenesis and immune responses of MD. First, chicken embryo fibroblasts (CEF) were stimulated with lipopolysaccharide (LPS) and/or recombinant chicken interferon-gamma (rChIFN-gamma) and used to develop techniques for examining transcription of IFN-alpha, IFN-gamma, inducible nitric oxide synthase (iNOS), interleukin (IL)-1beta, IL-2, IL-6 and IL-8 by reverse transcription-polymerase chain reaction (RT-PCR). Addition of LPS and/or rChIFN-gamma resulted in the up-regulation of mRNA for iNOS, IL-1beta and IL-6, while IFN-gamma was up-regulated by LPS alone. IL-2 was down-regulated by the treatments. Second, to determine the effects of Marek's disease herpesvirus (MDV) infection on cytokine transcription in vivo, chickens were infected with MDV at 21 days of age and examined at 7 days post-infection (p.i.) (exp. 1) or were infected with MDV at 1 day of age and examined from 3 to 15 days p.i. (exp. 2). In MDV-infected chickens, IFN-gamma transcription was up-regulated as early as 3 days p.i. until the termination of the experiment at 15 days p.i., while iNOS and IL-1beta were up-regulated between 6 and 15 days p.i. Infection of 1-day-old chicks increased levels of mRNA for IFN-gamma and iNOS between 16- and 64-fold at 9 days p.i. These results suggest that IFN-gamma and iNOS may play an important role in the pathogenesis of MD.

GATA-1 interacts with the myeloid PU.1 transcription factor and represses PU.1-dependent transcription

The GATA-1 transcription factor is capable of suppressing the myeloid gene expression program when ectopically expressed in myeloid cells. We examined the ability of GATA-1 to repress the expression and function of the PU.1 transcription factor, a central regulator of myeloid differentiation. We found that GATA-1 is capable of suppressing the myeloid phenotype without interfering with PU.1 gene expression, but instead was capable of inhibiting the activity of the PU.1 protein in a dose-dependent manner. This inhibition was independent of the ability of GATA-1 to bind DNA, suggesting that it is mediated by protein-protein interaction. We examined the ability of PU.1 to interact with GATA-1 and found a direct interaction between the PU.1 ETS domain and the C-terminal finger region of GATA-1. Replacing the PU.1 ETS domain with the GAL4 DNA-binding domain removed the ability of GATA-1 to inhibit PU.1 activity, indicating that the PU.1 DNA-binding domain, rather than the transactivation domain, is the target for GATA-1–mediated repression. We therefore propose that GATA-1 represses myeloid gene expression, at least in part, through its ability to directly interact with the PU.1 ETS domain and thereby interfere with PU.1 function.

GATA-1 interacts with the myeloid PU.1 transcription factor and represses PU.1-dependent transcription

The GATA-1 transcription factor is capable of suppressing the myeloid gene expression program when ectopically expressed in myeloid cells. We examined the ability of GATA-1 to repress the expression and function of the PU.1 transcription factor, a central regulator of myeloid differentiation. We found that GATA-1 is capable of suppressing the myeloid phenotype without interfering with PU.1 gene expression, but instead was capable of inhibiting the activity of the PU.1 protein in a dose-dependent manner. This inhibition was independent of the ability of GATA-1 to bind DNA, suggesting that it is mediated by protein-protein interaction. We examined the ability of PU.1 to interact with GATA-1 and found a direct interaction between the PU.1 ETS domain and the C-terminal finger region of GATA-1. Replacing the PU.1 ETS domain with the GAL4 DNA-binding domain removed the ability of GATA-1 to inhibit PU.1 activity, indicating that the PU.1 DNA-binding domain, rather than the transactivation domain, is the target for GATA-1–mediated repression. We therefore propose that GATA-1 represses myeloid gene expression, at least in part, through its ability to directly interact with the PU.1 ETS domain and thereby interfere with PU.1 function.

Development and use of monoclonal antibodies to chicken fibronectin to show that the chicken hepatocellular carcinoma cell line, LMH, constitutively expresses fibronectin

Fibronectin (Fn) is a high molecular weight glycoprotein and acute phase reactant that contributes to a variety of cellular activities including proliferation and wound healing. Production of Fn is influenced by cytokines such as IL-1alpha, IL-6 and TNF -alpha, and in serum Fn levels can function as an indicator of sepsis and reticulo-endothelial function. Here we describe the production of a panel of mAb to chicken Fn and give evidence that a chicken hepatocellular carcinoma cell line, LMH, constitutively expresses Fn. A capture ELISA to measure chicken Fn was developed using an IgG1 mAb (AV62) as the capture Ab, and biotinylated AV63 (IgG2b) as the detecting Ab. This study identified a single commercially available mAb directed against human Fn that also recognised chicken Fn. By contrast, the anti-chicken Fn mAbs did not cross-react with either human or bovine Fn.

Infectious bursal disease virus of chickens: pathogenesis and immunosuppression

Infectious bursal disease virus (IBDV) is an important immunosuppressive virus of chickens. The virus is ubiquitous and, under natural conditions, chickens acquire infection by the oral route. IgM+ cells serve as targets for the virus. The most extensive virus replication takes place in the bursa of Fabricius. The acute phase of the disease lasts for about 7-10 days. Within this phase, bursal follicles are depleted of B cells and the bursa becomes atrophic. Abundant viral antigen can be detected in the bursal follicles and other peripheral lymphoid organs such as the cecal tonsils and spleen. CD4(+) and CD8(+) T cells accumulate at and near the site of virus replication. The virus-induced bursal T cells are activated, exhibit upregulation of cytokine genes, proliferate in response to in vitro stimulation with IBDV and have suppressive properties. Chickens may die during the acute phase of the disease although IBDV induced mortality is highly variable and depends, among other factors, upon the virulence of the virus strain. Chickens that survive the acute disease clear the virus and recover from its pathologic effects. Bursal follicles are repopulated with IgM(+) B cells. Clinical and subclinical infection with IBDV may cause immunosuppression. Both humoral and cellular immune responses are compromised. Inhibition of the humoral immunity is attributed to the destruction of immunoglobulin-producing cells by the virus. Other mechanisms such as altered antigen-presenting and helper T cell functions may also be involved. Infection with IBDV causes a transient inhibition of the in vitro proliferative response of T cells to mitogens. This inhibition is mediated by macrophages which are activated in virus-exposed chickens and exhibit a marked enhancement of expression of a number of cytokine genes. We speculate that T cell cytokines such as interferon (IFN)-gamma may stimulate macrophages to produce nitric oxide (NO) and other cytokines with anti-proliferative activity. Additional studies are needed to identify the possible direct immunosuppressive effect of IBDV on T cells and their functions. Studies are also needed to examine effects of the virus on innate immunity. Earlier data indicate that the virus did not affect normal natural killer (NK) cell levels in chickens.

Regulation of chicken haemopoiesis by cytokines

The continuous production, control and functional activation of blood cells involves a complex series of cellular events in which a small population of stem cells generates large numbers of mature cells. The survival, proliferation and development of these cells is strictly dependent on extracellular signals, among these are polypeptide regulators generally known as cytokines. While a large number of mammalian cytokines with proliferative and inhibitory effects have been described in detail, it is surprising that comparatively little is known of the avian system. Given the success of human cytokines as a model, the ability to manipulate the chicken haemopoietic and lymphopoietic systems by precise application of purified cytokines provides a rational approach to defence against disease. As a general caveat, an increased awareness of the existence of regulatory networks and the likelihood that these regulators were designed to function most effectively when acting in combination, will provide an understanding into the regulation of haemopoiesis and hence find application in both clinical and agricultural research.

Cytokine therapy: a natural alternative for disease control

Disease control in food production animals is normally mediated through the use of vaccines, chemicals and antibiotics. However, the extensive use of antibiotics and chemicals in livestock has resulted in environmental and human health concerns, particularly with regard to the emergence of drug-resistant bacteria in the food chain. In fact, the World Health Organisation (WHO) has now urged meat producers to use environmentally-friendly alternative methods to control disease. Cytokines, as natural mediators of the immune response, offer exciting alternatives to conventional therapeutics. The utilisation of cytokines is becoming more feasible with the recent cloning of a number of cytokine genes. Since the chicken's immune system is similar to that of mammals, they offer an attractive model system with which to study the effectiveness of cytokine therapy in the control of disease in intensive livestock. In this report we will review our recent studies on the therapeutic potential of chicken interferon gamma (ChIFN-gamma) as a vaccine adjuvant and a growth promoter.

Functional analysis of carboxy-terminal deletion mutants of c-Myb

The c-myb gene is implicated in the differentiation and proliferation of hematopoietic cells. Truncations of the N and/or C terminus of c-Myb, found in v-Myb, can potentiate its transforming ability. Two negative regulatory subregions, located in the C terminus, were mapped previously by using GAL4-c-Myb fusion proteins in transient transfection assays for the transcriptional activation of a GAL4-responsive reporter gene. To dissect the C terminus of c-Myb in terms of its involvement in transcriptional activation and oncogenic transformation, a series of C-terminal deletion mutants of c-Myb were analyzed. In addition, linker insertion mutants within the transactivation domain and/or heptad leucine repeat of c-Myb were examined along with those deletion mutants. In this study, we demonstrated that the removal of both of the two previously mapped negative regulatory subregions from the native form of c-Myb not only supertransactivates a Myb-responsive reporter gene but also potentiates its transforming ability in culture. However, in contrast to previous results, cells transformed by all of the mutants analyzed here except v-Myb itself exhibited the same phenotype as those transformed by c-Myb. The proliferating cells were bipotenial and differentiated into both the granulocytic and monocytic lineages. This result implies that the C terminus of c-Myb alone has no effect on the lineage determination. Finally, the transactivation activities of these mutants correlated with their transforming activities when a mim-1 reporter gene was used but not when a model promoter containing five tandem Myb-binding sites was used. In particular, a very weakly transforming mutant with a linker insertion in the heptad leucine repeat superactivated the model promoter but not the mim-1 reporter gene.

Recombinant chicken IFN-gamma expressed in Escherichia coli: analysis of C-terminal truncation and effect on biologic activity

Interferon-gamma (IFN-gamma) possesses potent immunostimulatory properties, and it has recently been shown to have potential therapeutic properties. Recombinant protein technology is frequently used for commercial production of therapeutics, such as IFN. Biologically active recombinant chicken IFN-gamma (rChIFN-gamma) constructs bearing an N-terminal poly-His tag were expressed in Escherichia coli. Preparations of rChIFN-gamma contained varying ratios of a full-length and a truncated protein species (18 and 16 kDa, respectively). Amino acid sequence analysis of the full-length protein corroborated the sequence previously predicted from the cDNA sequence. Full-length rChIFN-gamma contains two cysteine residues at the C-terminus, and these were labeled by reduction and subsequent specific alkylation with fluorescent tag (5-I-AEDANS) to distinguish between full-length and C-terminally truncated forms of rChIFN-gamma. Comparative peptide mapping, amino acid sequencing, and mass spectrometry revealed that the 16 kDa protein was truncated at Lys133. It was also observed that the 18 kDa rChIFN-gamma protein was infrequently contaminated with small quantities of protein truncated at Arg141. A truncated recombinant construct (His1-Lys133) was also expressed in E. coli and had biologic activity comparable with that of the full-length construct. The 3-D structure of rChIFN-gamma was deduced by comparative modeling with bovine and human IFN-gamma crystallographic structures. Analysis of sequences and comparison of structures have revealed that the 3-D structure of rChIFN-gamma is similar to those of bovine and human molecules despite an overall amino acid identity of only 32%.

Recombinant fowlpox viruses coexpressing chicken type I IFN and Newcastle disease virus HN and F genes: influence of IFN on protective efficacy and humoral responses of chickens following in ovo or post-hatch administration of recombinant viruses

We have constructed recombinant (r) fowl pox viruses (FPVs) coexpressing chicken type I interferon (IFN) and/or hemagglutinin-neuraminidase (HN) and fusion (F) proteins of Newcastle disease virus (NDV). We administered rFPVs and FPV into embryonated chicken eggs at 17 days of embryonation or in chickens after hatch. Administration of FPV or rFPVs did not influence hatchability and survival of hatched chicks. In ovo or after hatch vaccination of chickens with the recombinant viruses resulted in protection against challenge with virulent FPV and NDV. Chickens vaccinated with FPV or FPV-NDV recombinant had significantly lower body weight 2 weeks following vaccination. This loss in body weight was not detected in chickens receiving FPV-IFN and FPV-NDV-IFN recombinants. Chickens vaccinated with FPV coexpressing IFN and NDV genes produced less antibodies against NDV in comparison with chickens vaccinated with FPV expressing NDV genes.

Vaccinia virus-encoded cytokine receptor binds and neutralizes chicken interferon-gamma

To counteract the host immune response, poxviruses have evolved secreted factors that bind cytokines and thereby neutralize their biological activities. The vaccinia virus B8R gene encodes a protein that neutralizes interferon-gamma (IFN-gamma) from several mammals including man, cow, rat, and rabbit but not mice. We now report that the activity of the B8R gene product is not restricted to cytokines of mammals: it also efficiently neutralized chicken IFN-gamma. B8R blocked chicken IFN-gamma-mediated induction of guanylate binding protein RNA in the chicken fibroblast cell line CEC-32 and secretion of nitric oxide in HD-11 cells. Radiolabeled baculovirus-expressed B8R efficiently bound to immobilized recombinant chicken IFN-gamma. Scatchard analysis revealed a binding constant of chicken IFN-gamma to B8R of approximately 0.5 nM. A mutant form of chicken IFN-gamma which lacks the 18 C-terminal amino acids and which has lost more than 99% of its biological activity was able to block the IFN-gamma-neutralizing effect of B8R. Binding studies showed that the mutant protein bound radiolabeled B8R only about threefold less well than wild-type chicken IFN-gamma but failed to compete with wild-type chicken IFN-gamma for binding to the cellular receptor. These results suggest that the extreme C terminus of chicken IFN-gamma is crucial for binding to its cellular receptor but less important for recognition by the viral cytokine receptor.

Distinct C/EBP functions are required for eosinophil lineage commitment and maturation

Hematopoietic differentiation involves the commitment of multipotent progenitors to a given lineage, followed by the maturation of the committed cells. To study the transcriptional events controlling these processes, we have investigated the role of C/EBP proteins in lineage choice of multipotent hematopoietic progenitors (MEPs) transformed by the E26 virus. We found that forced expression of either the alpha or beta isoforms of C/EBP in MEPs induced eosinophil differentiation and that in addition, C/EBPbeta could induce myeloid differentiation. Conversely, dominant-negative versions of C/EBPbeta inhibited myeloid differentiation. C/EBP-induced eosinophil differentiation could be separated into two distinct events, lineage commitment and maturation. Thus, eosinophils induced by transactivation-deficient C/EBPbeta alleles were found to be blocked in their maturation, whereas those expressing wild-type C/EBP proteins were not. Likewise, a 1-day activation of a conditional C/EBPbeta allele in multipotent progenitors led to the formation of immature eosinophils, whereas sustained activation produced mature eosinophils. These results show that C/EBP can induce both myeloid and eosinophil lineage commitment and that transactivation independent and dependent C/EBP functions are required during eosinophil lineage commitment and maturation, respectively.

Coadministration of IFN-gamma enhances antibody responses in chickens

The development of new generation vaccines has focused on the use of natural immunologic adjuvants that are capable of enhancing a protective immune response. The use of cytokines as immunomodulators in livestock animals, particularly poultry, is becoming more feasible with the recent cloning of several cytokine genes and the progression of new delivery technologies, such as live vectors and DNA delivery. Given that chickens are reared under intensive conditions that are conducive to infection by opportunistic pathogens, the primary mechanism for disease control in poultry is early and effective vaccination. However, many poultry vaccines offer only short-term protection or give nonuniform responses within flocks. We have developed a model system with which to measure the adjuvant potential of cytokines in chickens. This involves measuring antibody levels following coadministration of chicken interferon-gamma (Ch-IFN-gamma) with sheep red blood cells (SRBC). Groups of SPF and commercial broiler birds were injected with two different doses of SRBC with and without coadministration of Ch-IFN-y. Three weeks later, all birds were boosted with SRBC alone. Sera were collected weekly and anti-SRBC antibody titers (total Ig and IgG) were determined by hemagglutination. Priming Ch-IFN-gamma resulted in enhanced primary and secondary (IgG) antibody responses that persisted at higher levels when compared with birds that received SRBC alone. Second, coadministration of Ch-IFN-y allowed a 10-fold lower dose of antigen to be as effective as a high dose of antigen that was given without Ch-IFN-gamma. Third, treatment with Ch-IFN-y resulted in an increase in the proportion of birds responding to antigen challenge. These results suggest the potential use for Ch-IFN-gamma as a vaccine adjuvant.

PU.1 induces myeloid lineage commitment in multipotent hematopoietic progenitors

Little is known about the transcription factors that mediate lineage commitment of multipotent hematopoietic precursors. One candidate is the Ets family transcription factor PU.1, which is expressed in myeloid and B cells and is required for the development of both these lineages. We show here that the factor specifically instructs transformed multipotent hematopoietic progenitors to differentiate along the myeloid lineage. This involves not only the up-regulation of myeloid-specific cell surface antigens and the acquisition of myeloid growth-factor dependence but also the down-regulation of progenitor/thrombocyte-specific cell-surface markers and GATA-1. Both effects require an intact PU.1 transactivation domain. Whereas sustained activation of an inducible form of the factor leads to myeloid lineage commitment, short-term activation leads to the formation of immature eosinophils, indicating the existence of a bilineage intermediate. Our results suggest that PU.1 induces myeloid lineage commitment by the suppression of a master regulator of nonmyeloid genes (such as GATA-1) and the concomitant activation of multiple myeloid genes.

Avian macrophages: regulators of local and systemic immune responses

Macrophages are key regulatory cells of the immune system involved in initiating and directing the innate and specific immune responses, the systemic acute phase response, tissue repair, and tissue remodeling. In the early stages of a challenge from invading microorganisms or from tissue injury, macrophages defend local and systemic homeostasis by initiating a complex series of cellular, biochemical, and behavioral events. These pathophysiological adjustments are mediated by an extensive variety of communication molecules, including: cytokines, cytokine inhibitors, endocrine hormones, eicosanoids, neurotransmitters, and reactive oxygen intermediates. The cytokines produced by macrophages (monokines) are not well characterized relative to their mammalian counterparts, but a variety of chemokine, pro-inflammatory, and colony-stimulating factor activities have been described. Although the sequence homology, and thus species cross-reactivity, between avian and mammalian cytokines is typically low, the functional characteristics appear to be generally similar. The pro-inflammatory cytokines are important initiators and regulators of the local immune response. They are also released in sufficient quantities during some infections to coordinate a systemic acute phase response that impacts the growth, reproduction, and well-being of poultry. An understanding of the mechanisms and molecules used by macrophages to regulate immune and inflammatory responses may permit the development of products, diets, or husbandry techniques to modulate immunity for the enhancement of the productivity of poultry.

Mammalian granulocyte-macrophage colony-stimulating factor receptor expressed in primary avian hematopoietic progenitors: lineage-specific regulation of proliferation and differentiation

The cytokine Granulocyte-Macrophage Colony-Stimulating Factor (GM-CSF) regulates proliferation, differentiation, and apoptosis during myelopoiesis and erythropoiesis. Structure-function relationships of GM-CSF interactions with its receptor (GM-R), the biochemistry of GM-R signal transduction, and GM-CSF action in vivo are relatively well understood. Much less is known, however, about GM-R function in primary hematopoietic cells. In this paper we show that expression of the human GM-R in a heterologous cell system (primary avian erythroid and myeloid cells) confirms respective results in murine or human cell lines, but also provides new insights how the GM-R regulates progenitor proliferation and differentiation. As expected, the hGM-CSF stimulated myeloid progenitor proliferation and differentiation and enhanced erythroid progenitor proliferation during terminal differentiation. In the latter cells, however, the hGM-R only partially substituted for the activities of the erythropoietin receptor (EpoR). It failed to replace the EpoR in its cooperation with c-Kit to induce long-term proliferation of erythroid progenitors. Furthermore, the hGM-R alpha chain specifically interfered with EpoR signaling, an activity neither seen for the betac subunit of the receptor complex alone, nor for the alpha chain of the closely related Interleukin-3 receptor. These results point to a novel role of the GM-R alpha chain in defining cell type-specific functions of the GM-R.

Potential use of cytokine therapy in poultry

Newly hatched chickens are highly susceptible to infection during the first 2 weeks of life. The utilisation of cytokines as therapeutic agents in livestock animals, in particular poultry, has become more feasible with the recent cloning of cytokine genes and the progression of new technologies such as live vectors. We have constructed a live recombinant fowlpox virus (FPV) that expresses chicken myelomonocytic growth factor (fp/cMGF). Administration of fp/cMGF to chicks resulted in a marked and sustained increase in the number of circulating blood monocytes as well as an increase in their state of activation, as measured by enhanced phagocytic activity and elevated production of nitric oxide. We have recently cloned the gene for chicken interferon-gamma (ChIFN-gamma). Recombinant ChIFN-gamma was capable of protecting chick fibroblasts from undergoing virus-mediated lysis and induced nitrite secretion from chicken macrophages in vitro. Preliminary vaccination trials have indicated that co-administration of ChIFN-gamma with antigen (sheep red blood cells) resulted in enhanced secondary (IgG) antibody responses and allowed a 10-fold lower dose of antigen to be used. Furthermore, administration of ChIFN-gamma resulted in enhanced weight gain in chicks and improved their resistance to disease challenge. The ability of cytokines to combat infection and enhance vaccine efficacy makes them excellent candidates as a therapeutic agents and adjuvants.

Enhanced expression of cytokine genes in spleen macrophages during acute infection with infectious bursal disease virus in chickens

We examined the effects of infectious bursal disease virus (IBDV) on splenic T cells and macrophages. In acute IBDV infection, splenocytes responded poorly to Con A stimulation. However, when T cells were isolated from whole spleen cells, purified T cells responded normally to Con A. This result indicated that functional T cells were present in the spleen but mitogen-induced proliferation of T cells was being suppressed by other cells. Previous studies indicated that soluble factors from suppressor cells may mediate this inhibition of T cell mitogenesis. We thus examined the effects of IBDV on spleen adherent cells. Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to quantitate the expression of several cytokine genes in splenic macrophages. In acute IBDV infection, splenic macrophages exhibited enhanced gene expression of type I interferon (IFN), chicken myelomonocytic growth factor (cMGF), an avian homolog of mammalian IL-6, and 9E3/CEF4, an avian homolog of mammalian IL-8. Mitogen-stimulated spleen cell cultures also produced elevated levels of nitric oxide. The elevation of cytokine gene expression by macrophages occurred transiently during the acute phase of viral infection and coincided with in vitro inhibition of T cell mitogenic response of spleen cells.

Structure of the chicken interferon-gamma gene, and comparison to mammalian homologues

The sequence of the chicken interferon-gamma (ifn-gamma) gene was determined, one of the first non-mammalian cytokine gene structures to be elucidated. Initial genomic clones were amplified from chicken genomic DNA and were used to isolate a cosmid clone covering the entire gene for sequencing. The exon:intron structure of chicken ifn-gamma is very similar to those of its mammalian homologues, with the exception of the third intron, which is markedly shorter in the chicken. The first exon contains both 5' UTR and signal sequence and the first 22 aa of the mature protein. The remainder of the coding region lies in exons 2-4. Exon 4 also encodes the stop codon and the 3' UTR, including two possible polyadenylation signals. A number of potential regulatory sequences similar to those found in mammals have been identified, in the promoter, in each intron and in the 3' UTR. In the promoter, these include the TATAATA- and CCAT-boxes, a consensus GATA motif in the reverse orientation and a potential NF-kappa B binding site. Other regulatory elements identified in the promoters of mammalian ifn-gamma genes are absent. Internal to the gene structure, regulatory sequences identified include elements found in the DNase I hypersensitivity region of the first intron of the human ifn-gamma gene and several potential NF-kappa B binding sites. The 3' UTR contains an AT-rich sequence, including nine repeats of the 'instability' motif ATTTA. As in mammals, chicken ifn-gamma is a single copy gene. The gene is highly conserved, with no polymorphisms yet identified using either RFLP or SSCP in the coding region. However, promoter sequence polymorphisms between different inbred lines of chickens have been identified, with possible links to disease resistance.