Avian CD Nomenclature Workshops, Montreal, June 1991, Budapest, August 1992 and Tours, September 1992

Delineation of chicken immune markers in the era of omics and multicolor flow cytometry

Multiparameter flow cytometry is a routine method in immunological studies incorporated in biomedical, veterinary, agricultural, and wildlife research and routinely used in veterinary clinical laboratories. Its use in the diagnostics of poultry diseases is still limited, but due to the continuous expansion of reagents and cost reductions, this may change in the near future. Although the structure and function of the avian immune system show commonalities with mammals, at the molecular level, there is often low homology across species. The cross-reactivity of mammalian immunological reagents is therefore low, but nevertheless, the list of reagents to study chicken immune cells is increasing. Recent improvement in multicolor antibody panels for chicken cells has resulted in more detailed analysis by flow cytometry and has allowed the discovery of novel leukocyte cell subpopulations. In this article, we present an overview of the reagents and guidance needed to perform multicolor flow cytometry using chicken samples and common pitfalls to avoid.

Identification of novel chicken CD4⁺ CD3⁻ blood population with NK cell like features

Chicken NK cells have been defined in embryonic spleen and intestinal epithelium as CD8(+) lymphoid cells that lack BCR and TCR, whereas blood NK cells have not been phenotypically defined. Here we employed the mab, 8D12 directed against CHIR-AB1, a chicken Fc receptor, to define a previously uncharacterized lymphoid cell population in the blood. Although CHIR-AB1 expression was found on several cell populations, cells with extraordinary high CHIR-AB1 levels ranged between 0.4 and 2.8% in five different chicken lines. The widespread applicability of the CHIR-AB1 mab was unexpected, since CHIR-AB1-like genes form a polygenic and polymorphic subfamily. Surprisingly the CHIR-AB1 high cells coexpressed low MHCII, low CD4 and CD5, while other T cell markers CD3 and CD8, the B cell marker Bu1, the macrophage marker KUL01 were absent. Moreover, they stained with the mab 28-4, 20E5 and 1G7, which define chicken NK cells and they also expressed CD25, CD57, CD244 and the vitronectin receptor (αVβ3 integrin). In functional assays, PMA stimulation led to high levels of IFNγ release, while spontaneous cytotoxicity was not detectable. The expression of typical NK cell markers in the absence of characteristic B- or T-cell markers, and their IFNγ release is suggestive of a yet unidentified NK like population.

Chicken thrombocytes express the CD51/CD61 integrin

A panel of commercially available anti-human mab was screened for cross-reactivity on chicken cells. All mab were screened at least twice on PBL collected from two different chicken lines. Out of the 377 mab tested, only two consistently reacted with subpopulations of PBL. The mab HUH73A reactive with CD11a was detected on all lymphocytes. In contrast, the mab 23C6 obtained from Serotec and reactive with an epitope formed by humanVbeta3 integrin chains (CD51/CD61) reacted with all thrombocytes, but not with other cells. In double immunofluorescence analyses, the 23C6+ cells were found to coexpress the CD45 antigen and the chicken thrombocyte marker K1. The chicken genes encoding CD51 and CD61 were analyzed by database mining. The CD51 gene is encoded by a 43 kb region containing 30 exons on chicken chromosome 7, whereas the 16 kb CD61 gene consisted of 15 exons and was localized to chromosome 27. In conclusion, the mab 23C6 is a useful reagent to identify chicken thrombocytes.

Reversible disruption of thymic function by steroid treatment

The effect of steroid treatment on the thymic output of T cells was examined in an avian model. Recent thymic emigrants in chickens transiently express the chicken T cell Ag 1 thymocyte marker, and thymic function can be monitored indirectly by measuring the levels of TCR gene rearrangement excision circles in peripheral T cells. Both parameters were used to show that intensive steroid treatment induces thymic involution and a profound reduction in the supply of naive T cells to the periphery. Conversely, resident T cells in the peripheral lymphocyte pool were relatively spared. Thymopoiesis immediately recovered following cessation of steroid treatment, concurrent with restoration of the thymic output of newly formed T cells. Repopulation of the peripheral T cell pool recapitulated the ontogenetic pattern of gamma delta T cell replenishment before alpha beta T cell reseeding, thereby indicating the complete recovery of thymic function after a course of steroid treatment.

Gamma/delta T cell response of chickens after oral administration of attenuated and non-attenuated Salmonella typhimurium strains

Poultry represents an important source of Salmonella infection in man. Despite intensive research on immunity, little is known about the involvement of T cell sub-populations in the immunological response of chickens against infection with non-host-adapted Salmonella (S.) serovars. In this study, the T cell composition of blood lymphocytes (CD4(+)CD8(+); CD4(+)CD8(-); CD4(-)CD8(+); CD8(+)TcR1(+); CD8(-)TcR1(+), CD8(+)TcR1(-)) after oral administration of the non-attenuated S. typhimurium wild-type strain 421 (infection) or the attenuated vaccine strain Salmonella vac((R)) T (immunization) to day-old chicks was investigated and compared with non-treated chickens by flow cytofluorometry. Additionally, the occurrence of T cell sub-populations (CD4(+); CD8(+); TcR1(+)(gammadelta); TcR2(+)(alphabeta(1))) in ceca, spleen and bursa of Fabricius of the birds was studied immunohistologically. Blood samples and tissues were examined between days 1 and 12 of age. Chicks inoculated with S. typhimurium 421 or Salmonella vac((R)) T showed significantly elevated percentages of CD8(+)TcR1(+) in blood on days 7, 8 and 9, or on day 8 in comparison to control animals. The CD4 to CD8 cell ratio was about 3:1 in infected animals on day 5 of age. In the organs of treated chicks the numbers of CD8(+)(gammadelta) and TcR1(+)(gammadelta) cells had markedly increased on days 4 and 5 in ceca, 8 and 9 in the bursa and 9 and 12 in the spleen. Moreover, infected or vaccinated birds revealed larger quantities of CD4(+) and TcR2(+) T cells in ceca on days 4 and 5. As shown by double staining, the TcR1(+) cells in the organs of infected animals additionally carried the CD8 antigen. In conclusion, immunization of day-old chicks with the attenuated Salmonella live vaccine strain resulted in the same changes in T cell composition as seen after infection with the non-attenuated Salmonella wild-type strain, but at a lower level. The remarkable increase of CD8(+)TcR1(+)(gammadelta) double positive cells in treated birds indicates an important role of this cell sub-population in the immunological defense of chickens against Salmonella exposure.

Role of chicken IL-2 on gammadelta T-cells and Eimeria acervulina-induced changes in intestinal IL-2 mRNA expression and gammadelta T-cells

Continuous culture of concanavalin A (Con A)-activated spleen cells in the presence of chicken recombinant IL-2 (rIL-2) promoted preferential growth of gammadelta T-cells. These cells displayed a high level of spontaneous cytotoxicity against LSCC-RP9 tumor cells, an avian NK cell target. Stimulation of IL-2-dependent gammadelta T-cells with Con A induced IFN-gamma and IL-2 mRNA transcripts, whereas stimulation with rIL-2 induced only IFN-gamma mRNA. Subcutaneous injection of 3-week-old chickens with IL-2 DNA increased splenic cells, expressing the CD8 and gammadelta TCR antigens. To investigate the role of IL-2 and gammadelta T-cells in parasitic infection, chickens were orally infected with Eimeria acervulina and the expression of IL-2 mRNA transcripts in the spleen and duodenum and the percentage of gammadelta T-cells in the duodenum were examined. Following both, the primary and secondary infections, a significant enhancement of IL-2 mRNA transcripts in the spleen and intestine and increased percentage of intraepithelial gammadelta T-cells in the duodenum were observed. These results indicate that host immune responses to E. acervulina involve an up-regulation of IL-2 secretion and an increased duodenum gammadelta T-cells.

Cross-reactive anti-chicken CD4 and CD8 monoclonal antibodies suggest polymorphism of the turkey CD8alpha molecule

To measure turkey CD4 and CD8 T cell levels, the cross-reactivity of mouse anti-chicken CD4 and CD8 monoclonal antibodies (mAb) with turkey leucocytes was tested by flow cytometric analysis of blood obtained from individuals in five turkey lines. The turkey lines used included a randombred control population (RBC2), a subline (F) of RBC2 selected for increased 16-wk BW, and a sire line (A, B, and C) from each of three commercial turkey breeders. Peripheral blood lymphocytes were isolated and stained with single or dual color staining. The CT8 mAb (anti-chicken CD8alpha) failed to detect the CD8alpha molecule in some turkeys, and there were large line differences in ability to detect the CD8alpha molecule. However, certain anti-chicken CD8alpha mAb (3-298, 3-292, and 11-39) had good cross-reactivity with the turkey CD8alpha molecule. These present data indicate that the turkey CD8alpha molecule is polymorphic. Some anti-chicken CD4 mAb (CT4, 2-6, 2-35, and 7-125) were also cross-reactive with the turkey CD4 molecule. Immunoprecipitation and Western blotting showed that the 3-298 mAb precipitated a 33- to 35-kDa polypeptide from the turkey splenocyte lysate under reducing conditions. The availability of cross-reactive anti-chicken CD4 and CD8 mAb will facilitate the studies of immune responses in turkeys.

Molecular and functional characterization of chicken IL-15

A cDNA encoding chicken interleukin-15 was cloned from a CD4+ T cell hybridoma expression library by screening with a rabbit antibody against a protein fraction of conditioned medium containing T cell growth promoting activity. The chicken IL-15 cDNA contains an open reading frame of 143 amino acids with a single potential N-linked glycosylation site. The predicted m.w. of the encoded protein (16 kDa) matched the size of an immunoreactive band on Western blots of E. coli expressing the recombinant IL-15. Amino acid and nucleotide sequence analyses of chicken IL-15 revealed 31% and 46% identity with bovine IL-15 respectively and lesser homologies to other mammalian IL-15s. Chicken IL-15 contained all 4 highly conserved cysteine residues present in mammalian IL-15 sequences. RT-PCR demonstrated that the chicken IL-15 gene is expressed in many tissues including spleen, intestine, and muscle and in established macrophage, T lymphoma and fibroblast cell lines. Activation of spleen cells with Con A enhanced the expression of IL-15 gene transcripts in a time-dependent manner. CHO-K1 cells transfected with the chicken IL-15 cDNA secreted a biologically active protein supporting the growth of Con A activated spleen lymphocytes. Continuous culture of spleen Con A lymphoblasts with chicken IL-15 over two months resulted in an enriched T lymphocyte population expressing the gammadeltaTCR, CD8alpha, and CD3 cell surface antigens.

Analysis of the immunological cross reactivities of 213 well characterized monoclonal antibodies with specificities against various leucocyte surface antigens of human and 11 animal species

213 Monoclonal antibodies (mAbs) raised against leucocyte surface antigens from human and 11 animal species were analyzed for reactivities against leucocytes from human and 15 different animal species. We found 77 mAbs (36%) to cross-react. Altogether, 217 cross reactions were registered out of 3195 possible combinations (7%). Most of the cross reacting mAbs had integrin or MHC class II specificities. This study defined cross reactions on the following markers: CD1a, 1c, 2, 4, 5, 8, 9, 11a, 11b, 14, 18, 20, 21, 23, 29, 31, 41, 43, 44, 45, 45R, 46, 49, 61, 62L, TCR gamma/delta, BCR, Thy-1, MHC class I and MHC class II, Swine-WC7 and Cattle-WC1. In order to characterize the molecular weight (MW) of the corresponding cross reacting antigens, selected mAbs were used to immunoprecipitate the antigens. The MW's of the analyzed precipitated antigens were in good agreement with the MWs of the homologous antigens. The followed strategy was found to be efficient and economical in defining new leucocyte antigen reactive mAbs.

Characterisation of chicken monocytes, macrophages and interdigitating cells by the monoclonal antibody KUL01

The distribution, function and ontogeny of the mononuclear phagocyte system of the chicken were characterised using the monoclonal antibody (MAb) KUL01. KUL01 specifically recognises chicken monocytes, macrophages and interdigitating cells, as well as activated microglia cells. Its tissue distribution allowed to discriminate KUL01 from all earlier described MAb, reactive with mononuclear phagocytes. The specificity of KUL01 for mononuclear phagocytes was further confirmed in functional assays: KUL01-positive macrophages in spleen and liver actively took up colloidal carbon, while monocytes and spleen and gut macrophages contained non-specific esterase and acid phosphatase activities characteristic for antigen-processing. Further, it was demonstrated that KUL01-reactive peripheral blood monocytes express MHC-II, but not CD4. In all tissues investigated, the same morphological subtypes of macrophages were detected in chicken at similar localisations as in mammals, indicating a high degree of conservation between the mononuclear phagocyte system of the chicken and of mammals.

Thymic function can be accurately monitored by the level of recent T cell emigrants in the circulation

Expression of the avian chT1 thymocyte antigen persists on a subpopulation of peripheral T cells enriched in the DNA deletion circles created by alphabeta and gammadelta TCR gene rearrangements. The chT1+ cells are evenly distributed among all of the peripheral T lymphocyte compartments. The levels of chT1+ T cells in the periphery gradually decline in parallel with age-related thymic involution, and these cells disappear following early thymectomy. Experiments in which variable numbers of the 14 thymic lobes are removed in young chicks indicate a direct correlation between the levels of circulating chT1+ cells and residual thymic mass. Measurement of recent thymic emigrants in the periphery thus provides an accurate indication of thymic function.

Chicken B-cell marker chB6 (Bu-1) is a highly glycosylated protein of unique structure

The chB6 molecule is expressed on chicken B cells throughout most of their development, as well as on some non-lymphoid cells. It has long been used as an allotypic marker in important studies of B-cell development, though its function is unknown. We isolated a chB6 cDNA by expression cloning and sequenced two further alleles following polymerase chain reaction amplification. The results show that chB6 is a typical type I transmembrane protein, highly glycosylated in the extracellular region and carrying a large intracellular region. It has no recognizable similarity to known mammalian molecules and thus represents a unique B-cell marker. Its presence in chickens may be related to differences in the properties of B-cell development between chickens and mammalian species. The sequences of the different alleles of this gene revealed a higher level of polymorphism than expected. A restriction fragment length polymorphism linked to the CHB6 gene has been used to determine its location on the linkage map of the chicken genome, which will allow the definitive evaluation of reported associations with disease resistance.

Characterization of chicken CD8-specific monoclonal antibodies recognizing novel epitopes

CD8 is a heterodimeric cell surface glycoprotein expressed primarily on thymocytes and a subpopulation of mature T lymphocytes. It binds to the invariant part of the major histocompatibility complex class I molecule and participates in antigen recognition by the major histocompatibility complex class I restricted T cells. As in mammalian species, the majority of chicken thymocytes express both CD4 and CD8, whereas peripheral T cells are either CD4- or CD8-positive. We have created a panel of mouse monoclonal antibodies detecting different cell surface epitopes on chicken CD8. The antibodies precipitate a 32-34 kDa dimeric protein from surface labelled thymocytes under reducing conditions. The identical N-deglycosylation pattern confirms that these MoAb precipitate the same heterodimeric molecule from chicken thymocyte lysates. Binding of 11-38 and 11-39 MoAb to peripheral blood T cells is totally inhibited by 11-39 and previously characterized CT8 and EP72 MoAb, further confirming their CD8 specificity. CD8 alpha-chain specificity of MoAb 11-39, 11-38, 11-30 and 11-13 is conclusively proven by staining COS-cells transfected with a plasmid containing CD8 alpha cDNA. However, MoAb 11-13, 11-30 and 11-38 do not compete with MoAb 11-39 in binding to CD8. These results demonstrate recognition of different epitopes by these MoAb. Monoclonal antibodies detecting novel epitopes on chicken CD8 provide a valuable tool for further studies on T cell development.

Survivors of bursal B cell production and emigration

The bursa of Fabricius is the site of primary B cell generation in the chicken. Analysis of the rate of bursal cell emigration demonstrated that about 1% of the blood B cell pool was replaced per hour by bursal emigrants. Surgical bursectomy distinguished three populations of blood B cells. About 60% of blood B cells in 3-wk-old chickens were short lived, with a lifespan of 2 to 3 d, and included most bursal emigrants. These cells migrate directly from the bursal follicular cortex to the periphery, express the LT2 antigen, and are proposed to represent a diversified repertoire of B cell specificities that have emigrated from the bursa in the absence of interaction with environmentally derived antigens in the follicular medulla. About 35% of blood B cells were much longer lived cells, having a lifespan exceeding 2 wk. These cells represent about 10% of bursal emigrants, which do not express the LT2 antigen and do not divide in the peripheral blood following emigration from the bursa. This population may represent cells that have undergone positive selection in the bursa by interacting with environmentally derived antigens and should, therefore, contain a restricted repertoire of B cell specificities. The third population, about 5% of blood B cells, were short-lived cells that represent the progeny of postbursal B cell production. The frequency of these cells progressively increases with time, taking over from the short-lived bursal emigrants as the bursa involutes, likely as a diversified repertoire of B cell specificities.

Characterization of avian natural killer cells and their intracellular CD3 protein complex

Natural killer (NK) cell activity appears to be conserved throughout vertebrate development but NK cells have only been well characterized in mammals. Candidate NK cells have been identified in the chicken as cytoplasmic CD3+ and surface T cell receptor (TCR)/CD3- (TCRO) lymphocytes that often express CD8. The fact that the TCRO cells are abundant in the embryonic spleen before T cells enter this organ allowed us to cultivate the embryonic TCRO cells using growth factors derived from activated adult lymphocytes. These TCRO cells were cytotoxic for an NK target cell line. They expressed cell surface CD8, a putative interleukin-2 receptor, CD45 and a receptor for IgG, but did not express CD4, major histocompatibility complex class II or immunoglobulin. Biochemical analysis of the cytoplasmic CD3 antigen revealed two of the three CD3 gamma, delta and epsilon homologues, and RNA transcripts for the third. The CD3 monoclonal antibody also precipitated a 32-kDa dimer that may represent a heterodimer of different CD3 constituents. TCR alpha and beta gene transcripts were not detected in the TCRO cells. These results indicate that the avian TCRO cell is the mammalian NK cell homologue. The shared evolutionary features of T cells and NK cells in birds and mammals support the idea that they derive from a common progenitor.