Production and characterisation of monoclonal antibodies specific for chicken interleukin-2

A novel monoclonal antibody against porcine macrophage colony-stimulating factor (CSF1) detects expression on the cell surface of macrophages

Macrophage colony-stimulating factor (CSF1) controls the proliferation and differentiation of cells of the mononuclear phagocyte system through binding to the receptor CSF1R. The expression and function of CSF1 has been well-studied in rodents and humans, but knowledge is lacking in other veterinary species. The development of a novel mouse anti-porcine CSF1 monoclonal antibody (mAb) facilitates the characterisation of this growth factor in pigs. Cell surface expression of CSF1 was confirmed on differentiated macrophage populations derived from blood and bone marrow monocytes, and on lung resident macrophages, the first species for this to be confirmed. However, monocytes isolated from blood and bone marrow lacked CSF1 expression. This species-specific mAb delivers the opportunity to further understanding of porcine myeloid cell biology. This is not only vital for the role of pigs as a model for human health, but also as a veterinary species of significant economic and agricultural importance.

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.

Development of novel reagents to chicken FLT3, XCR1 and CSF2R for the identification and characterization of avian conventional dendritic cells

Conventional dendritic cells (cDC) are bone marrow-derived immune cells that play a central role in linking innate and adaptive immunity. cDCs efficiently uptake, process and present antigen to naïve T cells, driving clonal expansion of antigen-specific T-cell responses. In chicken, vital reagents are lacking for the efficient and precise identification of cDCs. In this study, we have developed several novel reagents for the identification and characterization of chicken cDCs. Chicken FLT3 cDNA was cloned and a monoclonal antibody to cell surface FLT3 was generated. This antibody identified a distinct FLT3^HI splenic subset which lack expression of signature markers for B cells, T cells or monocyte/macrophages. By combining anti-FLT3 and CSF1R-eGFP transgenic expression, three major populations within the mononuclear phagocyte system were identified in the spleen. The cDC1 subset of mammalian cDCs express the chemokine receptor XCR1. To characterize chicken cDCs, a synthetic chicken chemokine (C motif) ligand (XCL1) peptide conjugated to Alexa Fluor 647 was developed (XCL1^AF647 ). Flow cytometry staining of XCL1^AF647 on splenocytes showed that all chicken FLT3^HI cells exclusively express XCR1, supporting the hypothesis that this population comprises bona fide chicken cDCs. Further analysis revealed that chicken cDCs expressed CSF1R but lacked the expression of CSF2R. Collectively, the cell surface phenotypes of chicken cDCs were partially conserved with mammalian XCR1⁺ cDC1, with distinct differences in CSF1R and CSF2R expression compared with mammalian orthologues. These original reagents allow the efficient identification of chicken cDCs to investigate their important roles in the chicken immunity and diseases.

Regulation and function of macrophage colony-stimulating factor (CSF1) in the chicken immune system

Macrophage colony-stimulating factor (CSF1) is an essential growth factor to control the proliferation, differentiation and survival of cells of the macrophage lineage in vertebrates. We have previously produced a recombinant chicken CSF1-Fc fusion protein and administrated it to birds which produced a substantial expansion of tissue macrophage populations. To further study the biology of CSF1 in the chicken, here we generated anti-chicken CSF1 antibodies (ROS-AV181 and 183) using CSF1-Fc as an immunogen. The specific binding of each monoclonal antibody was confirmed by ELISA, Western blotting and immunohistochemistry on tissue sections. Using the anti-CSF1 antibodies, we show that chicken bone marrow derived macrophages (BMDM) express CSF1 on their surface, and that the level appears to be regulated further by exogenous CSF1. By capture ELISA circulating CSF1 levels increased transiently in both layer and broiler embryos around the day of hatch. The levels of CSF1 in broilers was higher than in layers during the first week after hatch. Antibody ROS-AV183 was able to block CSF1 biological activity in vitro and treatment of hatchlings using this neutralising antibody in vivo impacted on some tissue macrophage populations, but not blood monocytes. After anti-CSF1 treatment, CSF1R-transgene reporter expressing cells were reduced in the bursa of Fabricius and cecal tonsil and TIM4⁺ Kupffer cells in the liver were almost completely ablated. Anti-CSF1 treatment also produced a reduction in overall bone density, trabecular volume and TRAP⁺ osteoclasts. Our novel neutralising antibody provides a new tool to study the roles of CSF1 in birds.

ADGRE1 (EMR1, F4/80) Is a Rapidly-Evolving Gene Expressed in Mammalian Monocyte-Macrophages

The F4/80 antigen, encoded by the Adgre1 locus, has been widely-used as a monocyte-macrophage marker in mice, but its value as a macrophage marker in other species is unclear, and has even been questioned. ADGRE1 is a seven transmembrane G protein-coupled receptor with an extracellular domain containing repeated Epidermal Growth Factor (EGF)-like calcium binding domains. Using a new monoclonal antibody, we demonstrated that ADGRE1 is a myeloid differentiation marker in pigs, absent from progenitors in bone marrow, highly-expressed in mature granulocytes, monocytes, and tissue macrophages and induced by macrophage colony-stimulating factor (CSF1) treatment in vivo. Based upon these observations, we utilized RNA-Seq to assess the expression of ADGRE1 mRNA in bone marrow or monocyte-derived macrophages (MDM) and alveolar macrophages from 8 mammalian species including pig, human, rat, sheep, goat, cow, water buffalo, and horse. ADGRE1 mRNA was expressed by macrophages in each species, with inter-species variation both in expression level and response to lipopolysaccharide (LPS) stimulation. Analysis of the RNA-Seq data also revealed additional exons in several species compared to current Ensembl annotations. The ruminant species and horses appear to encode a complete duplication of the 7 EGF-like domains. In every species, Sashimi plots revealed evidence of exon skipping of the EGF-like domains, which are highly-variable between species and polymorphic in humans. Consistent with these expression patterns, key elements of the promoter and a putative enhancer are also conserved across all species. The rapid evolution of this molecule and related ADGRE family members suggests immune selection and a role in pathogen recognition.

Analysis of the function of IL-10 in chickens using specific neutralising antibodies and a sensitive capture ELISA

In mammals, the inducible cytokine interleukin 10 is a feedback negative regulator of inflammation. To determine the extent to which this function is conserved in birds, recombinant chicken IL-10 was expressed as a secreted human Ig Fc fusion protein (chIL-10-Fc) and used to immunise mice. Five monoclonal antibodies (mAb) which specifically recognise chicken IL-10 were generated and characterised. Two capture ELISA assays were developed which detected native chIL-10 secreted from chicken bone marrow-derived macrophages (chBMMs) stimulated with lipopolysaccharide (LPS). Three of the mAbs detected intracellular IL-10. This was detected in only a subset of the same LPS-stimulated chBMMs. The ELISA assay also detected massive increases in circulating IL-10 in chickens challenged with the coccidial parasite, Eimeria tenella. The same mAbs neutralised the bioactivity of recombinant chIL-10. The role of IL-10 in feedback control was tested in vitro. The neutralising antibodies prevented IL-10-induced inhibition of IFN-γ synthesis by mitogen-activated lymphocytes and increased nitric oxide production in LPS-stimulated chBMMs. The results confirm that IL-10 is an inducible feedback regulator of immune response in chickens, and could be the target for improved vaccine efficacy or breeding strategies.

Development and characterisation of monoclonal antibodies reactive with porcine CSF1R (CD115)

Macrophage colony-stimulating factor (CSF1) controls the proliferation and differentiation of cells of the mononuclear phagocyte system. CSF1, alongside a second ligand, interleukin-34 (IL-34), acts by binding to a cell surface receptor (CSF1R). We previously cloned and expressed pig CSF1 and IL-34. Here we produced a pig CSF1R-Ig+pFUSE Fc fusion protein and used it as an immunogen to produce three monoclonal antibodies (ROS8G11, ROS3A5 and ROS3B10) targeted against porcine CSF1R. Specific binding of each monoclonal antibody was confirmed by ELISA, Western blot, flow cytometry and immunocytochemistry. The antibodies did not block CSF1 signalling. The surface expression of CSF1R in pig peripheral blood was restricted to CD14-positive monocytes and was also detected on lung macrophages. These antibodies provided an opportunity to investigate the increase of available CSF1R during pig BMDM differentiation. The new monoclonal antibodies provide useful reagents to support the study of monocyte and macrophage biology in the pig.

Production and characterisation of a monoclonal antibody that recognises the chicken CSF1 receptor and confirms that expression is restricted to macrophage-lineage cells

Macrophages contribute to innate and acquired immunity as well as many aspects of homeostasis and development. Studies of macrophage biology and function in birds have been hampered by a lack of definitive cell surface markers. As in mammals, avian macrophages proliferate and differentiate in response to CSF1 and IL34, acting through the shared receptor, CSF1R. CSF1R mRNA expression in the chicken is restricted to macrophages and their progenitors. To expedite studies of avian macrophage biology, we produced an avian CSF1R-Fc chimeric protein and generated a monoclonal antibody (designated ROS-AV170) against the chicken CSF1R using the chimeric protein as immunogen. Specific binding of ROS-AV170 to CSF1R was confirmed by FACS, ELISA and immunohistochemistry on tissue sections. CSF1 down-regulated cell surface expression of the CSF1R detected with ROS-AV170, but the antibody did not block CSF1 signalling. Expression of CSF1R was detected on the surface of bone marrow progenitors only after culture in the absence of CSF1, and was induced during macrophage differentiation. Constitutive surface expression of CSF1R distinguished monocytes from other myeloid cells, including heterophils and thrombocytes. This antibody will therefore be of considerable utility for the study of chicken macrophage biology.

Development of reagents to study the turkey's immune response: cloning and characterisation of two turkey cytokines, interleukin (IL)-10 and IL-13

The cDNAs of two turkey cytokines, interleukin (IL)-10 and IL-13, were cloned using oligonucleotide primers designed from their chicken orthologues. The coding regions of the chicken and turkey genes are highly conserved, with IL-10 and IL-13 exhibiting 94.1% and 90% nucleotide and 92% and 79.9% amino acid identity respectively. Both showed consistent mRNA expression in turkey lymphoid and gut tissues. Expression in non-lymphoid tissues was more variable but generally highest in the skin and trachea. Recombinant turkey IL-10 was expressed and bioactivity demonstrated by inhibition of IFN-γ synthesis from activated splenocytes. Chicken and turkey IL-10 cross-reacted in functional assays.

Chicken interleukin-21 is costimulatory for T cells and blocks maturation of dendritic cells

In mammals, interleukin-21 (IL-21) is an immunomodulatory cytokine with pleiotropic effects on the proliferation, differentiation and effector functions of T, B, NK and dendritic cells. A cDNA encoding the chicken orthologue of IL-21 (chIL-21) was cloned by RT-PCR from RNA isolated from activated chicken splenocytes and consists of 438 nucleotides, encoding an open reading frame of 145 amino acids (aa). Chicken IL-21 has 20-30% aa identity to its orthologues in mammals, Xenopus and fish, but is more highly conserved within Aves (50-80%). The four alpha-helical bundle structure of mammalian IL-21 appears to be conserved in the predicted chicken protein, as are the four cysteine residues required for the formation of two disulphide bridges. A glutamine residue in aa position 129, which has been implicated in the binding of IL-21 to the IL-2 receptor γ-chain in mammals, is also conserved. ChIL-21 is expressed in most lymphoid tissues, predominantly by CD4+ TCRαβ+ T cells. As in mammals, chIL-21 synergistically enhances T-cell proliferation and inhibits maturation of dendritic cells.

Production and characterisation of monoclonal antibodies specific for chicken interleukin-12

Using genetic immunisation of mice, we produced antibodies against chicken interleukin-12p40 (chIL-12p40), also known as IL-12β. After a final injection with a recombinant chIL-12p40 protein, several stable hybridoma cell lines were established which secreted monoclonal antibodies (mAbs) to this component of the heterodimeric IL-12 cytokine. Specific binding of three of the mAbs to COS-7 cell-derived recombinant chIL-12p40 and the chIL-12p70 heterodimer was demonstrated in an indirect ELISA, and in dot blots. Two of the mAbs were used to develop a capture ELISA, suitable for detecting both recombinant protein (chIL-12p40 and the heterodimeric p70 protein) and native chIL-12. The mAbs were further characterised to show utility in immunocytochemistry.

Identification of functional domains of chicken interleukin 2

Interleukin 2 (IL-2) is an essential cytokine that plays a pivotal role in the replication, maturation and differentiation of lymphocytes. In this study, the functional domains of chicken IL-2 (chIL-2) were mapped with monoclonal antibodies (mAb), a synthetic peptide, and a phage display peptide library. Nine neutralizing mAbs to chIL-2 were produced using the recombinant chIL-2 monomer expressed in prokaryotic cells as an immunogen and used to finely map the functional domains of the chIL-2 protein. The mimotopes of nine anti-chIL-2 mAbs, including KIELPSL, EHLDXNDSLYL, NHLXGXY, WHLPPSL, EFKASXL, TENPFPE, SGLYL, AHGYWEL and HHGYWEL, were respectively identified by phage display and peptide-competitive ELISA. These mimotopes constitute three conformational functional domains in the chIL-2 molecule, that is, N(26)K(27)I(28)H(29)L(30)E(31)L(32)P(35)Q(43)Q(44)T(45)L(46)Q(47)C(48)Y(49)L(50) (domain I), E(68)E(69)F(70)K(79)K(82)S(83)L(84)T(85)G(86)L(87) (domain II) and N(88)H(89)G(91)K(104)F(105)P(106)D(107)E(111)L(112)Y(118)L(119) (domain III). The neutralizing mAbs to chIL-2 inhibited the in vitro lymphocyte proliferation stimulated by three peptide domains of chIL-2. The predicted tertiary structure of chIL-2 reveals that domain I was positioned in the long A-B loop and the N terminal of Helix B, domain II was mostly situated in Helix C, and domain III was distributed in the C-D loop and Helix D. These data demonstrate the functional domains of chIL-2 and provide a clue for elucidating the interaction between chIL-2 and its receptor.

Characterization of the first nonmammalian T2 cytokine gene cluster: the cluster contains functional single-copy genes for IL-3, IL-4, IL-13, and GM-CSF, a gene for IL-5 that appears to be a pseudogene, and a gene encoding another cytokinelike transcript, KK34

A genomics approach based on the conservation of synteny was used to develop a bacterial artificial chromosome (BAC) contig across the chicken T2 cytokine gene cluster. Sequencing of representative BACs showed that the chicken genome encodes genes for the homologs of mammalian interleukin-3 (IL-3), IL-4, IL-5, IL-13, and granulocyte-macrophage colony-stimulating factor (GM-CSF). These sequences represent the first T2 cytokines found outside of mammals, and their location demonstrates that the T2 cluster is ancient (at least 300 million years old). Four of these genes (IL-3, IL-4, IL-13, and GM-CSF) are expressed at the mRNA level and can be expressed as recombinant protein. In contrast to the other four genes, the chicken IL-5 (ChIL-5) gene we sequenced lacks a recognizable promoter and regulatory sequences in the predicted 3'-untranslated region (3'-UTR). Further, there is no evidence for its expression at the mRNA level. We, therefore, hypothesize that it is a pseudogene. Genomic analysis revealed that a recently characterized cytokinelike transcript, KK34, not identified in our initial analysis of the BAC sequence, is also encoded in this cluster. This gene may represent a duplication of an ancestral IL-5 gene and may encode the functional homolog of IL-5 in the chicken.

Generation of monoclonal antibodies to porcine interleukin 6 (PIL-6) using the recombinant PIL-6 expressed in Escherichia coli

Porcine interleukin-6 (PIL-6) protein without signal peptide was expressed as a glutathione S-transferase (GST) fusion protein in Escherichia coli. The fusion protein was expressed in an insoluble fraction, however, it was solubilized by refolding procedure using urea. From the solubilized protein, the recombinant PIL-6 (rPIL-6) was purified by a batch method using glutathione sepharose 4B and PreScission protease cleavage. By the B3B1 hybridoma cell proliferation assay, biological activity of the purified rPIL-6 was confirmed. Three monoclonal antibodies (MAbs) named 2B-1, 5A-8 and 4C-3 were generated by using the rPIL-6 as an immunogen. Immunoglobulin isotypes of the MAbs were IgG2a (4C-3) and IgG2b (2B-1 and 5A-8). For the epitope analysis, additive enzyme-linked immunosorbent assay and immunoblot analysis using deletion mutants of PIL-6 were performed. These experiments revealed that the two MAbs (2B-1 and 5A-8) recognize an overlapped epitope and the other (4C-3) recognizes a distinct epitope, and all epitopes reside in the region of aa26-64 of PIL-6.

Embryonic age influences the capacity for cytokine induction in chicken thymocytes

Thymocyte responses to functional activation are of relevance to the evaluation of the efficacy of in ovo immunotherapies and vaccines in chickens. In this study we have demonstrated differences in chicken thymocyte responses according to developmental age. RNA samples from stimulated and unstimulated chicken thymocytes were assayed for messenger RNA encoding the cytokines interleukin-1beta (IL-1beta), IL-2, interferon-alpha (IFN-alpha), IFN-beta, IFN-gamma and transforming growth factor-beta4 (TGF-beta4), and also components of the major histocompatibility complex (MHC), beta2-microglobulin (beta2M) and the MHC class I alpha-chain (MHC IA). At embryonic day 14 thymocytes were least responsive to functional activation and differences existed even between thymocyte populations at embryonic day 18 and day 1 post-hatch. The duration of proliferation in response to stimulation was found to increase with increasing embryonic age. Mitogen stimulation of embryonic day 18 and day 1 post-hatch thymocytes induced up-regulation of IFN-gamma, IL-1beta and TGF-beta transcripts, and down-regulation of IFN-alpha, IFN-beta and IL-2 transcripts, with a higher induction of IFN-gamma, IL-1beta and TGF-beta transcripts in more immature T-cell-receptor-negative (TCR-) than TCR+ (TCR1+, TCR2+, or TCR3+) subsets. In contrast, in the mouse and human, both mature and immature thymocytes respond to mitogen stimulation with up-regulation of IL-2. Thymocytes from embryonic day 14 chicks responded to mitogen with a short burst of unsustained proliferation, and transcriptional down-regulation of the cytokines IL-2, IL-1beta, IFN-alpha, IFN-beta and IFN-gamma. These results suggest that embryonic day 14 thymocytes are largely unresponsive to mitogen. Transcripts encoding TGF-beta and type I interferons (IFN-alpha and IFN-beta) were constitutively expressed at high levels in very early thymocytes at embryonic day 14. Thymocytes at embryonic days 14 and 18 and day 1 post-hatch responded to mitogen stimulation with up-regulation of MHC IA transcript. The pattern of beta2M transcription following mitogen stimulation was distinct from that of the globally up-regulated MHC IA transcript, with up-regulation of beta2M transcription observed at embryonic day 18 and day 1 post-hatch but not at embryonic day 14. In thymocyte subsets, up-regulation of beta2M transcription was found to be specific to the CD8+ TCR+ population. The balance of responses in the embryonic thymus suggests that at all stages thymocytes have a reduced capacity for activation in comparison to mature thymocyte populations.

Differential effects of age on chicken heterophil functional activation by recombinant chicken interleukin-2

Interleukin-2 (IL-2) exercises an array of biological effects on many cells including the functional activation of cells of the innate immune response. Heterophils, the avian equivalent of the neutrophil, function as professional phagocytes to aid in regulation of innate host defenses. The objective of the present studies was to examine the effects of recombinant chicken IL-2 (rChIL-2) on functional activities of heterophils from chickens during the first 3 weeks after hatch. Peripheral blood heterophils were isolated and incubated with either COS cell-derived rChIL-2 or supernatants from mock-transfected COS cells. rChIL-2 had no effect on the functional activities of heterophils from day-of-hatch chickens, but significantly increased the phagocytosis and bactericidal activity of heterophils from 7- and 14-day-old chickens. rChIL-2 induced no direct stimulation of the respiratory burst by heterophils, but primed heterophils from 7- and 14-day-old birds for an enhanced respiratory burst in response to phorbol ester stimulation. Lastly, rChIL-2 had neither direct nor priming effects on heterophil degranulation. The enhancing effects on heterophil functional activity by rChIL-2 were abated by a neutralizing anti-chicken IL-2 mAb and were therefore specific for this cytokine. These results show that rChIL-2 can directly activate chicken heterophils to exert effector functions, and that heterophil activation by rChIL-2 is also an age-dependent event.

Interleukin-2 directly induces activation and proliferation of chicken T cells in vivo

Cytokines, as immune activators, have been investigated in mammalian systems as natural adjuvants and therapeutics. In particular, interleukin-2 (IL-2) has been studied widely as a vaccine adjuvant and immuno-enhancer because of its role in activating T cell proliferation. We show here that the first nonmammalian IL-2 gene cloned, chicken IL-2 (ChIL-2), exhibits similar biologic activities to those of mammalian IL-2. To assess the activities of ChIL-2 in vivo, we injected birds with recombinant ChIL-2 (rChIL-2) protein. rChIL-2 treatment induced peripheral blood lymphocytes to express cell surface IL-2 receptors (IL-2R) within 48 h and resulted in an increase in the proportion of peripheral blood CD4+ and CD8+ T cells. Using bromodeoxyuridine (BrdU) incorporation as a measurement of cell proliferation, we showed the increase in T cell populations to be due to cell proliferation. The ability of ChIL-2 to cause both activation and proliferation of T cells in vivo indicates that it has the potential to be used as an immune activator.