Monoclonal antibodies against chicken Bu-1a and Bu-1b alloantigens

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.

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.

Molecular characterization of Bu-1 and TLR2 gene in Haringhata Black chicken

Haringhata Black is the only registered indigenous poultry genetic resource of West Bengal till date. Molecular characterization of HB revealed that Bu-1 to be highly glycoylated transmembrane protein unlike mammalian Bu-1, whereas TLR2 of HB chicken was observed to be rich in Leucine rich repeat. HB chicken was observed to be genetically close to chicken of Japan, while distant to chicken breed of UK and Chicago. Avian species wise evolution study indicates genetic closeness of HB chicken with turkey. Differential mRNA expression profile for the immune response genes (TLR2, TLR4 and Bu1 gene) were studied for HB chicken with respect to other chicken breed and poultry birds, which reveals that HB chicken were better in terms of B cell mediated immunity and hence better response to vaccination. Hence HB chicken is one of the best poultry genetic resources to be reared under backyard system where biosecurity measures are almost lacking.

Intraganglionic macrophages: a new population of cells in the enteric ganglia

The enteric nervous system shares embryological, morphological, neurochemical, and functional features with the central nervous system. In addition to neurons and glia, the CNS includes a third component, microglia, which are functionally and immunophenotypically similar to macrophages, but a similar cell type has not previously been identified in enteric ganglia. In this study we identify a population of macrophages in the enteric ganglia, intermingling with the neurons and glia. These intraganglionic macrophages (IMs) are highly ramified and express the hematopoietic marker CD45, major histocompatibility complex (MHC) class II antigen, and chB6, a marker specific for B cells and microglia in avians. These IMs do not express antigens typically associated with T cells or dendritic cells. The CD45⁺ /ChB6⁺ /MHCII⁺ signature supports a hematopoietic origin and this was confirmed using intestinal chimeras in GFP-transgenic chick embryos. The presence of green fluorescent protein positive (GFP⁺⁾ /CD45⁺ cells in the intestinal graft ENS confirms that IMs residing within enteric ganglia have a hematopoietic origin. IMs are also found in the ganglia of CSF1R^GFP chicken and CX3CR1^GFP mice. Based on the expression pattern and location of IMs in avians and rodents, we conclude that they represent a novel non-neural crest-derived microglia-like cell population within the enteric ganglia.

SH3 dependent cell death signaling of the avian chB6 alloantigen

In chickens, B cells develop in the bursa of Fabricius, a unique organ for B cell development. Most B cells will die within the bursa, mirroring cell losses seen in mammalian bone marrow as central tolerance is enforced at the transition to mature cells. B cell responses are shaped by a complex interplay of signals. Signals in addition to BCR that impact central tolerance have recently been described. We have been interested in chB6, a novel alloantigen on B cells in the chicken. chB6 is found in close proximity to the BCR and can trigger apoptosis after cross-linking by antibody. chB6 has two Ig domains, placing it within the CD2/SLAM family of molecules, but its cytoplasmic domain is unique. We have used a site-specific mutagenesis approach to show that an SH3 binding site in chB6 is required for the induction of apoptosis, suggesting parallels to CD2 signaling.

New insights into the DT40 B cell receptor cluster using a proteomic proximity labeling assay

In the vertebrate immune system, each B-lymphocyte expresses a surface IgM-class B cell receptor (BCR). When cross-linked by antigen or anti-IgM antibody, the BCR accumulates with other proteins into distinct surface clusters that activate cell signaling, division, or apoptosis. However, the molecular composition of these clusters is not well defined. Here we describe a quantitative assay we call selective proteomic proximity labeling using tyramide (SPPLAT). It allows proteins in the immediate vicinity of a target to be selectively biotinylated, and hence isolated for mass spectrometry analysis. Using the chicken B cell line DT40 as a model, we use SPPLAT to provide the first proteomic analysis of any BCR cluster using proximity labeling. We detect known components of the BCR cluster, including integrins, together with proteins not previously thought to be BCR-associated. In particular, we identify the chicken B-lymphocyte allotypic marker chB6. We show that chB6 moves to within about 30–40 nm of the BCR following BCR cross-linking, and we show that cross-linking chB6 activates cell binding to integrin substrates laminin and gelatin. Our work provides new insights into the nature and composition of the BCR cluster, and confirms SPPLAT as a useful research tool in molecular and cellular proteomics.

Establishment of an in vitro system representing the chicken gut-associated lymphoid tissue

The bursa of Fabricius is critical for B cell development and differentiation in chick embryos. This study describes the production in vitro, from dissociated cell suspensions, of cellular agglomerates with functional similarities to the chicken bursa. Co-cultivation of epithelial and lymphoid cells obtained from embryos at the appropriate developmental stage regularly led to agglomerate formation within 48 hours. These agglomerates resembled bursal tissue in having lymphoid clusters overlaid by well organized epithelium. Whereas lymphocytes within agglomerates were predominantly Bu-1a⁺, a majority of those emigrating onto the supporting membrane were Bu-1a⁻ and IgM⁺. Both agglomerates and emigrant cells expressed activation-induced deaminase with levels increasing after 24 hours. Emigrating cells were actively proliferating at a rate in excess of both the starting cell population and the population of cells remaining in agglomerates. The potential usefulness of this system for investigating the response of bursal tissue to avian Newcastle disease virus (strain AF2240) was examined.

The origin of IgG-containing cells in the bursa of Fabricius

The bursa of Fabricius of the chicken is known as a primary lymphoid organ for B-cell development. Morphologically, the origin of IgG-containing cells in the bursa has not been clear until now, because abundant maternal IgG (MIgG) is transported to the chick embryo and distributed to the bursal tissue around hatching. Thus, it has been difficult to find out whether these cells themselves biosynthesize IgG or if they acquire MIgG via attachment to their surface. Our present study employing in situ hybridization clarified that IgG-containing cells in the medulla of bursal follicles did not biosynthesize IgG. To study the role of MIgG in the development of those IgG-containing cells, MIgG-free chicks were established from surgically bursectomized hen (SBx-hen). We found that, on the one hand, deprivation of MIgG from chicks completely inhibited the development of IgG-containing cells in the medulla after hatching. On the other hand, administration of MIgG to MIgG-free chicks recovered the emergence of those cells. In addition, we observed that those cells did not bear a B-cell marker and possessed dendrites with aggregated IgG. These results demonstrate that IgG-containing cells in the medulla are reticular cells that capture aggregated MIgG. Moreover, we show that the isolation of the bursa from environmental stimuli by bursal duct ligation (BDL) suppressed the development of IgG-containing cells after hatching. Thus, it is implied that environmental stimulations play a key role in MIgG aggregations and dendritic distributions of aggregated MIgG in the medulla after hatching.

Acute paretic syndrome in juvenile White Leghorn chickens resembles late stages of acute inflammatory demyelinating polyneuropathies in humans

Background

Sudden limb paresis is a common problem in White Leghorn flocks, affecting about 1% of the chicken population before achievement of sexual maturity. Previously, a similar clinical syndrome has been reported as being caused by inflammatory demyelination of peripheral nerve fibres. Here, we investigated in detail the immunopathology of this paretic syndrome and its possible resemblance to human neuropathies.

Methods

Neurologically affected chickens and control animals from one single flock underwent clinical and neuropathological examination. Peripheral nervous system (PNS) alterations were characterised using standard morphological techniques, including nerve fibre teasing and transmission electron microscopy. Infiltrating cells were phenotyped immunohistologically and quantified by flow cytometry. The cytokine expression pattern was assessed by quantitative real-time PCR (qRT-PCR). These investigations were accomplished by MHC genotyping and a PCR screen for Marek's disease virus (MDV).

Results

Spontaneous paresis of White Leghorns is caused by cell-mediated, inflammatory demyelination affecting multiple cranial and spinal nerves and nerve roots with a proximodistal tapering. Clinical manifestation coincides with the employment of humoral immune mechanisms, enrolling plasma cell recruitment, deposition of myelin-bound IgG and antibody-dependent macrophageal myelin-stripping. Disease development was significantly linked to a 539 bp microsatellite in MHC locus LEI0258. An aetiological role for MDV was excluded.

Conclusions

The paretic phase of avian inflammatory demyelinating polyradiculoneuritis immunobiologically resembles the late-acute disease stages of human acute inflammatory demyelinating polyneuropathy, and is characterised by a Th1-to-Th2 shift.

Aiolos controls gene conversion and cell death in DT40 B cells

The Ikaros family transcription factor Aiolos is important for B cell function, since B cells of Aiolos-null mutant mice exhibit an activated phenotype, enhanced B-cell receptor (BCR) signalling response and develop a systemic lupus erythematosus (SLE) type autoimmune disease. Aiolos has also been reported to interact with anti-apoptotic Bcl-2 and Bcl-x(L) in T cells, but whether Aiolos regulates cell death has not been studied in B cells. Here we show that the disruption of Aiolos in the DT40 B cell line induces a cell death sensitive phenotype, as the Aiolos(-/-) cells are more prone to apoptosis by nutritional stress, BCR cross-linking, UV- or gamma-irradiation. Furthermore, the Aiolos(-/-) cells have defective Ig gene conversion providing evidence that Aiolos is needed for the somatic diversification of the BCR repertoire. The re-expression of DNA-binding isoform Aio-1 was able to restore the gene conversion defect of the Aiolos-deficient cells, whereas the introduction of dominant negative isofom Aio-2 had no effect on gene conversion, thus demonstrating the functional importance of alternative splicing within Ikaros family. Although the Aiolos(-/-) cells exhibit reduced expression of activation-induced cytidine deaminase (AID), ectopic AID overexpression did not restore the gene conversion defect in the Aiolos(-/-) cells. Our findings indicate that Aiolos may regulate gene conversion in an AID independent manner.

Origin of follicular dendritic cell in the chicken spleen

The ellipsoid-associated cell (EAC) is a blood-borne phagocytic cell, residing in the antigen trapping zone of the chicken spleen. Binding and endocytosis of betaGalactosidase (betaGal) are independent from the Fc and complement receptors, because sulfated polysaccharides, in a concentration manner, inhibit the bacterial antigen uptake. The betaGal-positive cells migrate to the periarterial lymphatic sheath (PALS), the preexisting germinal centers (GC), and form clusters with B- and T-cells. betaGal, E5G12 double positive cells on the surface of the ellipsoid and in the PALS, GC and clusters prove that the EACs carry the enzyme. The EAC and the follicular dendritic cell (FDC) express, 68.2 and E5G12 and, 74.3 and E5G12, antigens, respectively. During migration the cessation of 68.2 and expression of 74.3 indicate the differentiation of EAC to FDC. By day 14 the clusters had disappeared, and in several GC the presence of double positive cells (74.3 and betaGal; E5G12 and betaGal) showed that the clusters had developed to GC. The presence of betaGal(+) cells in the PALS, where interdigitating dendritic cells (IDC) cooperate with the T-cells, suggests that in the spleen alternate routes exist for the EAC differentiation to FDC: EAC to FDC: betaGal-loaded cells in the preexisting GC; and EAC through IDC to FDC: betaGal(+) EAC in the PALS and clusters. The EAC-FDC axis works exclusively inside the spleen; therefore; this system may be operated in pneumococcus infection.

Immune response to a killed infectious bursal disease virus vaccine in inbred chicken lines with different major histocompatibility complex haplotypes

The influence of MHC on antibody responses to killed infectious bursal disease virus (IBDV) vaccine was investigated in several MHC inbred chicken lines. We found a notable MHC haplotype effect on the specific antibody response against IBDV as measured by ELISA. Some MHC haplotypes were high responders (B201, B4, and BR5), whereas other MHC haplotypes were low responders (B19, B12 and BW3). The humoral response of 1 pair of recombinants isolated from a Red Jungle Fowl (BW3 and BW4) being identical on BF and BG, but different on BL, indicated that part of the primary vaccine response was an MHC II restricted T-cell dependent response. The humoral response in another pair of recombinant haplotypes originating in 2 different White Leghorn chickens being BF21, BL21, BG15 (BR4) and BF15, BL15, BG21 (BR5) on the MHC locus indicated that the BG locus may perform an adjuvant effect on the antibody response as well. Vaccination of chickens at different ages and in lines with different origin indicated that age and background genes also influence the specific antibody response against inactivated IBDV vaccine.

Characterization of lymphocyte subsets over a 24-hour period in Pineal-Associated Lymphoid Tissue (PALT) in the chicken

BACKGROUND

Homeostatic trafficking of lymphocytes in the brain has important relevance to the understanding of CNS disease processes. The pineal gland of the chicken contains large accumulations of lymphocytes that suggest an important role related to homeostatic circadian neuro-immune interactions. The purpose of this initial study was to characterize the lymphocyte subsets in the pineal gland and quantitate the distribution and frequency of lymphocyte phenotypes at two time points over the 24-hour light:dark cycle.

RESULTS

PALT comprised approximately 10% of the total pineal area. Image analysis of immunocytochemically stained sections showed that the majority of lymphocytes were CD3+ (80%) with the remaining 20% comprising B-cells and monocytes (Bu-1+), which tended to distribute along the periphery of the PALT. T-cell subsets in PALT included CD4+ (75-80%), CD8+ (20-25%), TCRalphabeta/Vbeta1+ (60%), and TCRgammadelta+ (15%). All of the T-cell phenotypes were commonly found within the interfollicular septa and follicles of the pineal gland. However, the ratios of CD8+/CD4+ and TCRgammadelta+/TCRalphabeta/Vbeta1+ within the pineal tissue were each 1:1, in contrast to the PALT where the ratios of CD8+/CD4+ and TCRgammadelta+/TCRalphabeta/Vbeta1+ each approximated 1:4. Bu-1+ cells were only rarely seen in the pineal interstitial spaces, but ramified Bu-1+ microglia/macrophages were common in the pineal follicles. Effects of the 24-h light:dark cycle on these lymphocyte-pineal interactions were suggested by an increase in the area of PALT, a decline in the density of TCRalphabeta/Vbeta1+ cells, and a decline in the area density of Bu-1+ microglia at the light:dark interphase (1900 h) compared to the dark:light interphase (0700 h).

CONCLUSION

The degree of lymphocyte infiltration in the pineal suggests novel mechanisms of neuro-immune interactions in this part of the brain. Our results further suggest that these interactions have a temporal component related to the 24-hour light:dark cycle and that CD8+ and TCRgammadelta+ T-cells are preferentially recruited to the pineal follicles. Pineal microglia/macrophages were common and represent an important candidate for mediating these lymphocyte-pineal interactions via secretion of cytokines and chemokines.

Oesophageal tonsil of the chicken

The oesophageal tonsil of the chicken is a novel member of the mucosal-associated lymphoid tissue (MALT), which is located around the entrance of the proventriculus. It consists of 6 to 8 single units, which are surrounded by a thin fibrous capsule. Each one is organised around the bottom of the longitudinal folds of the oesophagus, and serves as a 'tonsillar crypt'. Stratified squamous epithelium is infiltrated by lymphoid cells, i.e. T cells, plasma cells, macrophages, and dendritic cells, but not B cells, to form lymphoepithelium (LE). In the LE vimentin-, MHC II- and ATPase-positive cells possibly represent Langerhans' cells, but the appearance of 74.3 positive cells in the LE is unusual, because the 74.3 monoclonal antibody (mAb) recognises chicken follicular dendritic cells in the germinal centre and medulla of the bursal follicles. The subepithelial lymphoid tissue is organised into T- and B-dependent regions, which are the interfollicular areas and the germinal centres, respectively. Existence of high-endothelial venules in the interfollicular region suggests an extensive cellular connection between the oesophageal tonsil and the other lymphoid organs. In the resting oesophagus the lumen is closed, but during swallowing a bolus the crypt opens and the lymphoepithelium can be exposed to undigested food, antigens, infectious agents and vaccines. The location of the oesophageal tonsil, cranial to the stomach, may provide this organ with a unique role as compared to the other parts of the MALT; namely, it may contribute to the replication of infectious bursal disease virus (IBDV) and/or the pathogenesis of infectious bursal disease.

Genetic line effect on peripheral blood leukocyte cell surface marker expression in chickens

To determine the role of genetics in baseline lymphocyte parameters, several distinct lines of chickens were examined for differences in peripheral blood leukocyte (PBL) populations. Four highly inbred chicken lines (MHC congenic Fayoumi lines M15.2 and M5.1, and MHC congenic Leghorn lines G-B1 and G-B2), two advanced intercrosses [F5 (Broiler x G-B2) and F5 (Broiler x M15.2)], and an outbred population of broilers were used. Leukocytes isolated from healthy adult birds were labeled with monoclonal antibodies: chCD3, chCD4, chCD8, chBu-1, and hCD14. Flow cytometry was used to determine the total percentage of positively labeled cells for each surface marker in a sample, as well as the mean fluorescent intensity, or surface marker density, of a labeled subset. Significant line differences for percentage positive CD3 T cells and the ratio of B cells:T cells (represented by the Bu-1:CD3 ratio) were found. The effect of line was also significant for CD3 and CD8 T cell receptor density. Effects of sex and MHC on PBL cell surface marker expression were not significant in the lines examined. This study demonstrates the effect of genetic line on resting leukocyte composition of peripheral blood in the chicken lines examined. Observed PBL differences add to our growing knowledge of the varied roles that immune system status (defined by specific cell populations) and genetic background have in determining susceptibility and disease progression in chickens.

The avian chB6 alloantigen induces apoptosis in DT40 B cells

In avian species, B-lymphocytes develop in the bursa of Fabricius. Cells developing in the bursa are subject to signals regulating their survival, with the majority of cells dying by apoptosis within the bursa. However, the molecules delivering the signals influencing this life and death decision remain enigmatic. We have previously shown that antibodies against the chB6 alloantigen present on avian B-lymphocytes can induce a rapid form of cell death. Here we extend this finding by showing that anti-chB6 antibodies induce true apoptosis in DT40 cells without visible membrane damage. This apoptosis results in DNA degradation and morphologic changes characteristic of apoptosis. Furthermore, this apoptosis is coincident with a loss of mitochondrial membrane potential and is inhibited by either overexpression of bcl-x(L) or the presence of inhibitors of caspase 8, 9, or 3 activity. Collectively these data argue that chB6 may function as a novel death receptor on avian B-lymphocytes and support the use of DT40 as an amenable model to study the signaling involved in chB6-induced apoptosis.

Biocharacteristics shared by highly protective vaccines against Marek's disease

Attenuated serotype 1 Marek's disease virus strains vary widely in their protection properties. This study was conducted to elucidate which biocharacteristics of serotype 1 MDV strains are related with protection. Three pairs of vaccines, each one including a higher protective (HP) vaccine and a lower protective (LP) vaccine originating from the same MDV strain, were studied. Two other highly protective vaccines (RM1 and CVI988/BP5) were also included in the study. Comparison within pairs of vaccines showed that marked differences existed between the HP and the LP vaccines. Compared with LP vaccines, HP vaccines replicated better in vivo. Also, they induced a significant expansion of total T cells and of the helper and cytotoxic T cell lineages (CD45(+)CD3(+), CD4(+)CD8(-), CD4(-)CD8(+)) as well as a marked increase in the expression of the antigens of MhcI and MhcII on T cells. Thus, our results show that in vivo replication and early stimulation of the T-cell lineage are two characteristics shared by HP vaccines. However, comparison among the four HP vaccines that provided protection equal to that of CVI988 (RM1, CVI988/BP5, CVI988 and 648A80) revealed variability, especially regarding in vivo replication. Strains RM1 and CVI988/BP5 showed much stronger replication in vivo than the other two vaccine strains (CVI988 and 648A80). Thus, no single set of characteristics could be used to identify the most protective Marek's disease vaccines, implying, perhaps, that multiple mechanisms may be involved.

A Monoclonal Antibody against Chicken Thrombocytes Reacts with the Cells of Thrombocyte Lineage

A new mouse monoclonal antibody (mAb), HUKT was raised against chicken peripheral blood thrombocytes. The mAb HUKT appeared to detect a specific marker on the surface of chicken thrombocytes. Flow cytometry (FCM) analysis revealed that it did not react with cells from the normal thymus, bursa of Fabricius, six kinds of chicken cell lines, chicken erythrocytes or human platelets. In addition, HUKT(+) cells in peripheral blood leukocytes (PBL) were CD45(low), Bu-1a(-) and CD3(-) cells. Immunoblotting analysis showed that the molecule recognized by HUKT is a monomer with an apparent molecular weight of 150 kDa under non-reducing and reducing conditions. Tissue distribution studies revealed that only cells of thrombocyte lineage in bone marrow and embryonic blood cells were stained by HUKT. The HUKT mAb presented here may be useful for both ontogenetic studies of thrombocyte lineage and immunological studies in the chicken.

Characterization of leukocyte subtypes in chicken inner ear sensory epithelia

Human hearing and balance require intact inner ear sensory hair cells, which transduce mechanical stimuli into electrical signals that are transmitted to the brain. Loss of hair cells after birth in mammals is irreversible, whereas birds are able to regenerate hair cells after insult and demonstrate ongoing hair cell production in the vestibular epithelia. Leukocytes reside in undamaged sensory epithelia of the avian inner ear and increase in number after trauma, prior to the proliferation of hair cell progenitors. It has been hypothesized that leukocyte-produced growth factors or cytokines may be involved in triggering hair cell regeneration. Little is known about the specific leukocyte subtypes present in avian ear. Immunohistochemistry with a panel of monoclonal antibodies to chicken leukocytes was used to identify leukocyte subtypes in normal posthatch chicken ear sensory epithelia. The responsiveness of the leukocytes to aminoglycoside-induced damage was also observed. Based on immunocytochemical and morphological criteria, we quantified leukocyte subtypes in normal and drug-damaged auditory and vestibular sensory epithelia. Data indicate that lymphocytes (B and T cells) do not reside in normal or drug-damaged ear sensory epithelia at 1-3 days post insult but are present in adjacent nonsensory tissues. The most common leukocytes in inner ear sensory epithelia are ramified cells of the myeloid lineage. Many of these are MHC class II positive, and a small percentage are mature tissue macrophages. An absence of leukocytes in lesioned areas of the auditory sensory epithelium suggests they may not play a critical role in triggering hair cell regeneration.

Effects of 6-hydroxydopamine on the development of the immune system in chickens

It has been suggested that the sympathetic nervous system communicates with lymphocytes expressing cell surface receptors for neurotransmitters such as norepinephrine (NE), on the basis of the finding that neurotransmitters modify immune responses in mammalian species. We confirmed that chicken lymphocytes in the brusa of Fabricius, thymus and spleen expressed beta-adrenergic receptor (beta-AR) mRNA from embryonic day (E) 10 and that intracellular cAMP level was elevated by NE, suggesting that lymphocytes express functional beta-AR on their surface at an early embryonal stage. To clarify whether the nervous system is involved in the development of the immune system, the effects of 6-hydroxydopamine (6-OHDA), one of sympathectomizing agents, on chicken lymphocytes was investigated. A single injection of 6-OHDA at a dose of 400 microg into a chicken embryo was carried out at E7 or 14 (as referred to E7 group and E14 group, respectively). NE level and the relative proportion of Bu-1a(+), CD4(+) and CD8(+) cells in the spleen of 3-week-old chickens were not altered by 6-OHDA treatment. However, the proliferative responses and expression of IL-2 mRNA in spleen cells cultured with pokeweed mitogen were reduced in E7 group compared with those of control. Furthermore, in CD8(+) spleen cells of E14 group of 3-week-old chickens, the expression of beta-AR mRNA and the relative increase of intracellular cAMP stimulated with NE were significantly decreased. These results suggest that the sympathetic nervous system affects the development of the immune system.

Identification of an alternatively spliced isoform of the common cytokine receptor gamma chain in chickens

The common cytokine receptor gamma(gamma(c)) chain is shared by at least six cytokine receptors and plays a critical role in the regulation of immune responses. In this study, we discovered that, unlike mammals, chickens possess two different gamma(c) gene transcripts, chgamma(c)-a and chgamma(c)-b. Sequence comparisons between the cDNAs and a gamma(c) genomic clone isolated by PCR revealed that chgamma(c)-b contained an in-frame 78bp insertion between Gly-222 and Val-223 of the chgamma(c)-a sequence. This insertion most likely resulted from alternative splicing such that the fifth intron was not removed from the chgamma(c)-b transcript. Furthermore, while chgamma(c)-a and chgamma(c)-b transcripts were expressed equally in the spleen, thymus, bursa, and cecal tonsils, they were differentially expressed during the time course of Con A stimulation of splenic T lymphocytes. Western blot analysis of normal spleen lymphocytes identified 45, 53, and 64 kDa immunoreactive bands whereas only 64kDa band was detected in Con A-activated splenic lymphocytes. COS-7 cells transfected with chgamma(c)-b secreted approximately 42kDa proteins. Taken together, our results document that chickens express an alternative spliced gamma(c) receptor which is larger than the conventional transcript and this novel isoform generates soluble receptors in the transfected COS-7 cells.

Initiation of humoral immunity. II. The effects of T-independent and T-dependent antigens on the distribution of lymphocyte populations

The effect of injecting T-independent (lipopolysaccharide, LPS) and T-dependent (bovine serum albumin, BSA) antigens on the redistribution of lymphocyte populations in immature male chickens was investigated. In the blood, percentages of total T-cells (CD3+), T-helper cells (CD4+), and T-cytotoxic/suppressor cells (CD8+) significantly decreased post-LPS injection (PLI) but not post-BSA injection (PBI), while percentages of monocytes/thrombocytes (K1+) significantly increased PLI. Interleukin-1 receptor expression on blood lymphocytes increased significantly PLI and PBI. In the spleen, the percentages of total T-cells (CD3+) increased significantly PLI and PBI, macrophage (K1+) percentages increased significantly PLI, while B-cell percentages decreased significantly PLI. These results indicate that following antigen injection, there is a redistribution of peripheral blood lymphocytes (specifically T-lymphocytes) to secondary lymphoid organs and the kinetics and magnitude of the changes can differ according to the type of antigen used.

The avian ChB6 alloantigen triggers apoptosis in a mammalian cell line

Many developing B lymphocytes are deleted by apoptosis. However, the mechanism signaling their demise remains poorly understood. Like mammals, chicken B cells are selected during their development; >95% of the cells in the bursa of Fabricius die without entering the secondary immune system. The molecule chB6 (Bu-1) has been used as a marker to identify B cells in the chicken. ChB6 is a type I transmembrane glycoprotein whose function is enigmatic. We have provided evidence that chB6 can induce a rapid form of cell death exhibiting characteristics of apoptosis. Here we further examine cell death induced by chB6 in a transfected mouse cell line. ChB6 is shown to cause apoptosis in this cell line as detected by a TUNEL assay for DNA fragmentation. This apoptosis is subject to regulation by signals from growth factor or by Bcl-x(L). Furthermore, we show that Ab binding to chB6 leads to cleavage of caspase 8, caspase 3, and poly(ADP ribose) polymerase. Overall, these data support the hypothesis that chB6 is a novel death receptor on avian B cells.

Adjuvant effects of IL-1beta, IL-2, IL-8, IL-15, IFN-alpha, IFN-gamma TGF-beta4 and lymphotactin on DNA vaccination against Eimeria acervulina

Eight chicken cytokine genes (IL-1beta, IL-2, IL-8, IL-15, IFN-alpha, IFN-gamma, TGF-beta4, lymphotactin) were evaluated for their adjuvant effect on a suboptimal dose of an Eimeria DNA vaccine carrying the 3-1E parasite gene (pcDNA3-1E). Chickens were given two subcutaneous injections with 50 microg of the pcDNA3-1E vaccine plus a cytokine expression plasmid 2 weeks apart and challenged with Eimeria acervulina 1 week later. IFN-alpha (1 microg) or 10 microg of lymphotactin expressing plasmids, when given simultaneously with the pcDNA3-1E vaccine, significantly protected against body weight loss induced by E. acervulina. Parasite replication was significantly reduced in chickens given the pcDNA3-1E vaccine along with 10 microg of the IL-8, lymphotactin, IFN-gamma, IL-15, TGF-beta4, or IL-1beta plasmids compared with chickens given the pcDNA3-1E vaccine alone. Flow cytometric analysis of duodenum intraepithelial lymphocytes showed chickens that received the pcDNA3-1E vaccine simultaneously with the IL-8 or IL-15 genes had significantly increased CD3+ cells compared with vaccination using pcDNA3-1E alone or in combination with the other cytokine genes tested. These results indicate that the type and the dose of cytokine genes injected into chickens influence the quality of the local immune response to DNA vaccination against coccidiosis.

In vitro characterization of chB6 positive and negative cells from early avian embryos

Density gradient-separated embryonic spleen and bone marrow cells were enriched for chB6(+) cells with positive and negative selection procedures and magnetic cell sorting. The majority of chB6(+) cells, consisting of small, dense, strongly chB6(+) cells, were prone to apoptosis, which was further accentuated after exposure to monoclonal antibodies directed against chB6 alloantigen, but was largely inhibited by PDBU, leading to maintenance and frequently numerical increases of chB6(+) cells after an initial decline. sIgM(+) cells within that population followed a very similar pattern, suggesting a PDBU-induced upregulation of sIgM expression on a proportion of chB6(+) cells. The protective effect of PDBU on anti-chB6-exposed cells was confirmed with bursal lymphocytes and shown to be entirely PDBU concentration dependent. It was calculated that each 14-day embryonic spleen contained a minimum of 250,000 chB6(+) and 3000-4000 sIgM(+) cells, respectively. Endogenous apoptosis appeared to be increased with embryonic age, reaching a peak with bursal cells in the posthatching period. A second population of larger, less dense, and weak chB6(+) cells, often with vacuoles in a more abundant cytoplasm, differed functionally, expanding numerically in unstimulated cultures and being inhibited by PDBU. No sIgM(+) cells developed within this population. It is proposed that this chB6(+) fraction may represent progenitors of a previously suggested chB6(+) subset of macrophages, in contrast to the dense chB6(+), small cells, viewed as B cell progenitors. chB6(-) cells, consisting predominantly of granulocytes, proliferated vigorously in unstimulated cultures, but were consistently inhibited by PDBU. Coculture of age-matched embryonic bursal stroma with positively and negatively enriched chB6(+) cells revealed enhanced protection from apoptosis for chB6(+) cells and a PDBU-induced upregulation of sIgM expressing cells. Bursal stroma also had a pronounced positive effect on the proliferation of chB6(-) cells.

Perinatal deletion of B cells expressing surface Ig molecules that lack V(D)J-encoded determinants in the bursa of Fabricius is not due to intrafollicular competition

During embryonic development, the avian bursa of Fabricius selects B cell precursors that have undergone productive V(D)J recombination for expansion in oligoclonal follicles. During this expansion, Ig diversity is generated by gene conversion. We have used retroviral gene transfer in vivo to introduce surface Ig molecules that lack V(D)J-encoded determinants into B cell precursors. This truncated mu heavy chain supports both B cell expansion within embryo bursal lymphoid follicles and gene conversion. We show that individual follicles can be colonized exclusively by cells expressing the truncated mu chain and lacking endogenous surface IgM, ruling out a requirement for V(D)J-encoded determinants in the establishment of bursal lymphoid follicles. In striking contrast to their normal development in the embryo, bursal cells expressing the truncated mu-chain exhibit reduced rates of cell division and increased levels of apoptosis after hatching. The level of apoptosis in individual follicles reflects the proportion of cells within the follicle that express the truncated mu-chain. In particular, high levels of apoptosis are associated with follicles containing exclusively cells expressing the truncated micro receptor. Thus, apoptotic elimination of such cells is not due to competition within the follicle by cells expressing endogenous surface IgM receptors. This provides the first direct demonstration that the regulation of B cell development in the avian bursa after hatching differs fundamentally from that seen in the embryo. The requirement for intact IgM expression when the bursa is exposed to exogenous Ag implicates a role for Ag in avian B cell development after hatching.

Effects of photoperiod and melatonin on lymphocyte activities in male broiler chickens

Understanding the role of the pineal gland in regulating the immune response and the role of photoperiod in influencing pineal gland secretions are becoming increasingly important. The purposes of the present experiments were to investigate the effects of different photoperiod regimens on T- and B-lymphocyte activities in broiler chickens. Next, the influence of different photoperiod regimens on the responsiveness of lymphocytes to melatonin in vitro was examined. The effect of melatonin in vitro on lymphocyte activities was also studied, regardless of the photoperiod received. Finally, the effects of photoperiod on the profiles of different splenocyte cell types were investigated. To study the effect of photoperiod on lymphocyte activities, different photoperiod regimens were used. These were: constant lighting, 23 h light:1 h darkness; intermediate lighting, 12 h light:12 h darkness; and intermittent lighting, 1 h light:3 h darkness. Peripheral blood and splenic lymphocyte activities were tested at 3 and 6 wk of age by performing a mitogen cell-proliferation assay with a polyclonal T-cell mitogen, concanavalin A (Con A), and T-dependent B-cell mitogen, pokeweed mitogen (PWM). To study the effect of photoperiod on the responsiveness of lymphocytes to melatonin in vitro or the effect of melatonin in vitro on lymphocyte activities regardless of photoperiod received, lymphocytes from the chickens that were exposed to the different photoperiod regimens were incubated with mitogen and different concentrations of melatonin. To study the effect of photoperiod on profiles of different cell types, the percentages of splenocyte subpopulations from birds exposed to different photo-periods were determined using flow cytometry with CD4+, CD8+, CD3+, and B-cell markers. The results of these studies indicate that splenic T and B lymphocytes from 6-wk-old chickens grown in intermittent lighting had higher activities than those from chickens grown in constant lighting. Peripheral blood and splenic lymphocytes from chickens raised under constant lighting were more responsive to melatonin in vitro than those from chickens raised under intermittent lighting. This difference in response may be due to lower levels of melatonin in birds receiving constant lighting, making them more sensitive to melatonin in vitro. Melatonin in vitro enhanced the mitogenic response of peripheral blood T lymphocytes from 6-wk-old chickens, splenic T lymphocytes from 3-wk-old chickens, and splenic T and possibly B lymphocytes from 6-wk-old chickens. Finally, intermittent lighting increased the percentages of splenic CD4+, CD8+, and CD3+ cells but not B-cell subpopulations at 6 wk of age, presumably because of increased levels of melatonin in birds receiving intermittent lighting. Our results re-emphasize the importance of melatonin in regulating host immune response; this regulation could be accomplished through exposing broiler chicks to intermittent lighting.

Development of B cells expressing surface immunoglobulin molecules that lack V(D)J-encoded determinants in the avian embryo bursa of fabricius

Immunoglobulin gene rearrangement in avian B cell precursors generates surface Ig receptors of limited diversity. It has been proposed that specificities encoded by these receptors play a critical role in B lineage development by recognizing endogenous ligands within the bursa of Fabricius. To address this issue directly we have introduced a truncated surface IgM, lacking variable region domains, into developing B precursors by retroviral gene transfer in vivo. Cells expressing this truncated receptor lack endogenous surface IgM, and the low level of endogenous Ig rearrangements that have occurred within this population of cells has not been selected for having a productive reading frame. Such cells proliferate rapidly within bursal epithelial buds of normal morphology. In addition, despite reduced levels of endogenous light chain rearrangement, those light chain rearrangements that have occurred have undergone variable region diversification by gene conversion. Therefore, although surface expression of an Ig receptor is required for bursal colonization and the induction of gene conversion, the specificity encoded by the prediversified receptor is irrelevant and, consequently, there is no obligate ligand for V(D)J-encoded determinants of prediversified avian cell surface IgM receptor.

Epitopes for chicken monoclonal antibodies in spleens of selected Japanese quail lines

A line of Japanese quail selected for high plasma cholesterol is highly susceptible to diet-induced atherosclerosis. Lymphocyte epitopes recognized by mouse anti-chicken monoclonal antibodies (c-mAb), TCR-1, TCR-2, TCR-3. CD-3, CD-4, CD-8, and BU-1a/b were reacted with spleens from quail selected for high (HL) and low (LL) plasma total cholesterol and their nonselected controls (CL). Cross reactivity to c-mAb and effect of line and gender were immunohistochemically evaluated. Chicken spleens were positive controls. Quail were immunologically stimulated with either sheep red blood cells (SRBC) or Brucella abortus 2 weeks before spleens were removed. Quail spleen epitopes of all lines recognized TCR-3 and CD-8 c-mAb, but no other c-mAb. Number of reacting cells and staining intensity to the TCR-3 c-mAb were greater in the HL than in the LL regardless of the stimulating Ag or dose used. For the CD-8 c-mAb, there were no differences among lines in birds receiving SRBC. In B. abortus-immunized birds, sex x line interactions indicated that males of the HL and CL had lower responses than females but LL males were not different than females. TCR-3 and CD8 c-mAb may be useful in studying immunological mechanisms for atherosclerosis in Japanese quail.

Cloning and Modeling of the First Nonmammalian CD4

We have cloned and sequenced the first nonmammalian CD4 cDNA from the chicken using the COS cell expression method. Chicken CD4 contains four extracellular Ig domains that, in analogy to mammalian CD4, are in the order V, C2, V, and C2. The molecule is 24% identical with both human and mouse sequences. The extracellular domains were modeled using human and rat CD4 crystal structures as templates. In the first domain there are two extra Cys residues that are at suitable distance to form an intra-β-sheet disulfide bridge in addition to the canonical one in the V domain. The region responsible for the interaction with MHC class II is relatively nonconserved in chicken. However, there are positively charged amino acids in the C″ region of the N-terminal domain that may mediate the association to the negatively charged residues of the MHC class II β-chain. Molecular modeling also implies that the membrane-proximal domain mediates dimerization of chicken CD4 in a similar way as it does for human CD4. Furthermore, the cytoplasmic tail is highly conserved, containing the protein tyrosine kinase p56lck recognition site that is preceded by an adjacent di-leucine motif for the internalization of the molecule. Interestingly, there are no Ser residues in the cytoplasmic part, which may explain the slow down-regulation of chicken CD4 after phorbol ester stimulation.

Expression of Bcl-2 in inflammatory sites from patients with active Behçet's disease

Behçet's disease (BD) is a current systemic vasculitis of unknown aetiology. Eyes, skin, joints, the oral cavity, genital system, blood vessels, central nervous system and lung are usually involved. Defective regulation of programmed cell death (apoptosis) may play a role in the development of (BD), and the proto-oncogene Bcl-2 is involved in the control of apoptosis in immunocompetent cells. We therefore wished to investigate the expression of Bcl-2 in the peripheral lymphocytes and in two inflammatory sites of patients with active BD: bronchoalveolar lavage (BAL) and cerebrospinal fluid (CSF) lymphocytes. Levels of Bcl-2 expression in the lymphocytes of patients with BD and, for comparison, in the lymphocytes of healthy controls and non-inflammatory neurological diseases (NIND), were studied by two-colour cytofluorography and RNA analysis. In BD patients, a significant proportion of T cells expressed increased amounts of Bcl-2 protein, both in peripheral blood and in inflammatory sites. Mononuclear cells of patients with BD showed increased amount of Bcl-2 messenger RNA. The in vitro incubation of T lymphocytes with IL-10, significantly increased the Bcl-2 expression, specifically in T lymphocytes from inflammatory sites. In active BD, stimulation of HSV-1 T lymphocytes slightly increased Bcl-2 expression, not significantly different from unstimulated HSV-1 T cells. The occurrence of circulating T lymphocytes with abnormally high Bcl-2 expression in peripheral circulation and in inflammatory sites may be explained in part by the increased in vivo activation levels, and by aetiopathological agent(s): our findings seem to indicate an important role in the chronic inflammation in BD.

The Structure of Avian CD5 Implies a Conserved Function

The chicken CD5 cDNA was isolated by COS cell expression cloning utilizing a novel mAb 2-191. The cDNA contains a 1422-nucleotide open reading frame encoding a mature protein with 32% and 30% identity to mouse and human CD5 polypeptides, respectively. The molecule consists of a 330-amino acid extracellular region with three repeats of the scavenger receptor cysteine-rich domain, a 29-amino acid hydrophobic transmembrane domain, and a 93-amino acid cytoplasmic tail. The cytoplasmic region contains motifs that are highly conserved between species, including several potential phosphorylation sites. The chicken CD5 is a 64-kDa phosphorylated glycoprotein with a protein core of 57 kDa as determined by immunoprecipitation and SDS-PAGE analysis. αβ T cells express a homogeneously high level of CD5, whereas low or intermediate CD5 expression on γδ T cells depends on their tissue location. In contrast to human and mouse, CD5 is found at low levels on all chicken B cells. The high conservation of structural features, as well as signaling motifs, implies a conserved role for CD5 both in lymphocyte development and function.

Identification of chicken Bu-1 alloantigens using the monoclonal antibody AV20

The genetically polymorphic chicken antigen Bu-1 (chB6) has been identified by alloantisera raised against RPL line 6(3) (Bu-1a) and line 7(2) (Bu-1b) birds and subsequently by monoclonal antibodies (mAbs) which identify individual alloantigens. We have produced a monoclonal antibody, AV20, which recognises a monomorphic determinant on the antigen Bu-1. AV20 identifies a marker on both bursal and peripheral B cells. Staining characteristics on bursa, spleen, thymus and peripheral blood lymphocytes are similar to those of the allotypic antibodies which identify Bu-1a and Bu-1b. However, AV20 identified B cells in partially inbred birds as well as inbred lines including line 6(1) and line 7(2), indicating that it recognises a monomorphic determinant, AV20 immunoprecipitated an antigen with a Mwr of 150 kDa under non-reducing conditions and 70-75 kDa under reducing conditions indicating it is a homodimer. Serial immunoprecipitations or bursal-cell lysates from line 6(1) or line 7(2) confirmed that AV20 recognised the same antigen as mAbs against Bu-1a and Bu-1b in the respective lines.

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.

Role of YadA-mediated collagen binding in arthritogenicity of Yersinia enterocolitica serotype O:8: experimental studies with rats

Outer membrane protein YadA, Yersinia adhesin, is one of the plasmid-encoded virulence factors of yersiniae. YadA protects bacteria against host defense through several different mechanisms. One important role of YadA is to mediate binding to several collagen types. Our recent study revealed that a yadA null mutant of Yersinia enterocolitica serotype O:8 has a drastically reduced arthritogenic capacity when injected intravenously into Lewis rats. To further characterize the arthritogenic role of YadA, we repeated the rat experiments with strain Y. enterocolitica O:8/pYV082; this strain expresses a YadA deletion derivative lacking 22 amino acids from the amino-terminal hydrophobic region and does not bind to collagen. Y. enterocolitica O:8/pYV082 induced arthritis in 5 to 14% of rats inoculated with arthritogenic doses, whereas the arthritis incidence with the wild-type parent strain was 65%. The parent strain was slightly more virulent than Y. enterocolitica O:8/pYV082, as determined by rat mortality. It also frequently induced skin abscesses, whereas Y. enterocolitica O:8/pYV082 did not. Infection kinetics in spleen and mesenteric lymph nodes were about the same with both of the bacterial strains used, and the same was true of the Yersinia-specific antibody response. Altogether, these results suggest that YadA-mediated collagen binding contributes to the arthritogenicity of Y. enterocolitica O:8.

Loss of surface immunoglobulin expression precedes B cell death by apoptosis in the bursa of Fabricius

The vast majority of lymphocytes generated daily in the chicken bursa of Fabricius do not emigrate to the periphery but die in situ. Apoptotic cells in the bursa can be readily detected by the presence of fragmented DNA and by the large numbers of condensed cellular nuclei observed by electron microscopy. Consequently, most newly generated lymphocytes die by programmed cell death. We show that bursal cells divide rapidly and apoptotic cells are derived from rapidly dividing precursors. Analysis of the phenotype of bursal cells undergoing apoptosis demonstrated that cell death does not occur in the most mature bursal cell population and is therefore not random. High levels of surface Ig are expressed on bursal cells entering S phase of the cell cycle. In contrast, bursal cells in the early stages of apoptosis in vivo express very low to undetectable levels of surface Ig but were unequivocally confirmed as being of the B lineage by polymerase chain reaction (PCR) detection of rearranged Ig genes. Bursal cells induced to undergo apoptosis in vitro express high levels of surface Ig demonstrating that induction of apoptosis does not in itself induce a loss of surface Ig expression. Consequently, loss of surface Ig expression precedes bursal cell death by apoptosis in vivo, suggesting that maintenance of a threshold level of surface Ig may be a requirement for the continued progression of chicken B lymphocyte development in the bursa.

Role of YadA in arthritogenicity of Yersinia enterocolitica serotype O:8: experimental studies with rats

Outer membrane protein YadA, the Yersinia adhesin, is one of the plasmid-encoded virulence factors of yersiniae. To evaluate the role of YadA in the pathogenesis of reactive arthritis experimentally, we used YadA- strain YeO8-116, a kanamycin GenBlock insertion mutant derived from Yersinia enterocolitica O:8 wild-type strain 8081. As control strains, a plasmid-cured derivative (8081-c) of 8081 and a YopH- mutant (8081-yoph) were used. In addition, YeO8-116, with the yadA mutation transcomplemented with plasmid pMW10, was used. YeO8-116 induced arthritis to a considerably lesser extent than did wild-type strain 8081 when inoculated intravenously into Lewis rats. In rats surviving for over 14 days after the bacterial inoculation, the arthritis incidences were 6% (4 of 72) among those inoculated with the yadA mutant and 51% (33 of 65) among those inoculated with wild-type strain 8081. When the yadA gene was transcomplemented back to YeO8-116, YeO8-116/pMW10 induced arthritis in 47% (9 of 19) of the inoculated rats. Plasmid-cured strain 8081-c did not induce arthritis in any of the 24 inoculated rats, whereas YopH- mutant 8081-yoph induced arthritis in 20% (5 of 25) of the rats inoculated. Although the 50% lethal dose of YeO8-116 was about sixfold higher than that of 8081, the kinetics of bacterial elimination from the spleen and mesenteric lymph nodes were about the same with both strains. Antibody responses in rats infected with the two strains were also indistinguishable. Our results indicate that YadA contributes to the arthritogenicity of Y. enterocolitica in the rat model.

Postnatal development of intra-epithelial leukocytes in the chicken digestive tract: phenotypical characterization in situ

In the present study, we characterized intra-epithelial leukocytes in the digestive tract of chickens during postnatal development. Their phenotype was characterized by monoclonal antibodies in cryostat sections and the numbers of the different cell-types were counted in the epithelium of the esophagus, proventriculus, duodenum, jejunum, cecum, and colon. All intra-epithelial leukocytes bore the leukocyte-common antigen CD45; 35% were T lymphocytes, and 50% bore a B-cell marker. However, no immunoglobulin-bearing cells were detected in the epithelium. Monocytes and macrophages were found only in the epithelium of the esophagus. A remaining population of non-B, non-T, non-monocyte cells (15%) was present in all parts of the digestive tract. The number of intra-epithelial leukocytes was greatest in the duodenum and jejunum, and decreased in the proximal part of the cecum and in the colon. Intra-epithelial leukocytes were only sporadically detected in the proventriculus. The total number of intra-epithelial leukocytes increased until 8 weeks after hatching and then decreased at 18 months. In the esophagus, the total number of intra-epithelial leukocytes changed little during aging. We found that the intra-epithelial leukocytes of chickens and rodents are distinct in that chicken intra-epithelial leukocytes comprise a cell population that bears a B-cell antigen but that lacks surface immunoglobulins.

Retroviral transformation in vitro of chicken T cells expressing either alpha/beta or gamma/delta T cell receptors by reticuloendotheliosis virus strain T

Exposure of normal juvenile chicken bone marrow cells to the replication defective avian reticuloendotheliosis virus strain T (REV-T) (chicken syncytial virus [CSV]) in vitro resulted in the generation of transformed cell lines containing T cells. The transformed T cells derived from bone marrow included cells expressing either alpha/beta or gamma/delta T cell receptors (TCRs) in proportions roughly equivalent to the proportions of TCR-alpha/beta and TCR-gamma/delta T cells found in the normal bone marrow in vivo. Essentially all TCR-alpha/beta-expressing transformed bone marrow-derived T cells expressed CD8, whereas few, if any, expressed CD4. In contrast, among TCR-gamma/delta T cells, both CD8+ and CD8- cells were derived, all of which were CD4-. Exposure of ex vivo spleen cells to REV-T(CSV) yielded transformed polyclonal cell lines containing > 99% B cells. However, REV-T(CSV) infection of mitogen-activated spleen cells in vitro resulted in transformed populations containing predominantly T cells. This may be explained at least in part by in vitro activation resulting in dramatically increased levels of T cell REV-T(CSV) receptor expression. In contrast to REV-T(CSV)-transformed lines derived from normal bone marrow, transformed lines derived from activated spleen cells contained substantial numbers of CD4+ cells, all of which expressed TCR-alpha/beta. While transformed T cells derived from bone marrow were stable for extended periods of in vitro culture and were cloned from single cells, transformed T cells from activated spleen were not stable and could not be cloned. We have therefore dissociated the initial transformation of T cells with REV-T(CSV) from the requirements for long-term growth. These results provide the first demonstration of efficient in vitro transformation of chicken T lineage cells by REV-T(CSV). Since productive infection with REV-T(CSV) is not sufficient to promote long-term growth of transformed cells, these results further suggest that immortalization depends not only upon expression of the v-rel oncogene but also on intracellular factor(s) whose expression varies according to the state of T cell physiology and/or activation.

Bursa-dependent subpopulations of peripheral B lymphocytes in chicken blood

By selective labeling of juvenile chicken bursal cells with colloidal fluorescein isothiocyanate in situ, the emigration rate of bursal lymphocytes to the periphery was estimated at approximately 0.84% and 0.96% of the peripheral blood lymphocyte (PBL) and splenic B cell pool per hour, respectively. Emigrant bursal cells were found primarily in blood and spleen, with very small numbers migrating to thymus, bone marrow, and gut-associated lymphoid tissues. Emigrant bursal cells expressed high levels of both major histocompatibility complex class II antigen and the Ov alloantigen, a phenotype found on a population comprising approximately 4% of bursal cells from which the bursal emigrants may be derived. Surgical bursectomy at 3 weeks of age revealed that peripheral blood B cells could be divided into three distinct populations. Specifically, 60% of the peripheral blood B cells were short lived with a half-life of about 30 h in the blood. These cells accounted for the great majority of emigrants from the bursa to the peripheral blood. Approximately 35% of PBL B cells had a half-life of 12 days following bursectomy and comprised cells which did not divide in the periphery. Consequently, we propose that physiological differences between this population and the majority of bursal emigrants are established intrabursally. The remaining PBL B cells, whose relative proportion increases with age from about 5% of PBL B cells at 2-3 weeks of age, are short lived and are being continually produced from (a) post-bursal site(s) of B cell production.

Involvement of the avian mu heavy chain in recolonization of the bursa of Fabricius

In the chicken, the B cells develop in a specialized organ, the bursa of Fabricius. Earlier it was shown that neonatal bursal cells treated with polyclonal anti-chicken immunoglobulin antibodies are not able to recolonize the bursa when transferred into cyclophosphamide-treated chicks. In this study, 4-day-old bursal cells were treated with different polyclonal and monoclonal anti-immunoglobulin antibodies and transferred into 4-day-old cyclophosphamide-treated chickens. Two monoclonal anti-chicken IgM antibodies, CVI-59.7 and 21-2B2, recognizing distinct epitopes of the mu heavy chain, were inhibitory. Incubation of cells with 21-2B2 antibody caused about 90% inhibition of bursal recolonization. After incubation with CVI-59.7 antibody the inhibition was 50%. The high inhibition by 21-2B2 antibody was also seen when F(ab')2 fragments of the antibody were used. These results suggest that the entry of the cells needed for bursal recolonization is inhibited almost totally by 21-2B2 antibody, or that this antibody blocks further proliferation of the cells in bursal follicles. In conclusion, we have shown that a mu heavy chain epitope is intimately involved in the recolonization of bursal follicles, and distinct epitopes of the mu heavy chain are not equally important in this process.

Expression of immunoglobulin genes in the avian embryo bone marrow revealed by retroviral transformation

Analysis of the early stages of avian B lymphocyte differentiation has been hampered by the low frequency of extra-bursal B lineage cells in sites of hematopoiesis. Consequently, little is known about B lineage precursors prior to their migration into the bursa of Fabricius. Colonization of the bursa typically occurs between about days 8 and 14 of embryonic (e) development, although cells which can colonize the bursa, functionally defined as pre-bursal stem cells, can be demonstrated in embryo bone marrow up until about the time of hatch. As a novel approach to analyzing early stages of avian B lymphocyte development, we show here that transformed B lineage cells can be derived from chick embryo bone marrow after infection in vitro with the replication-defective retrovirus REV-T produced in the context of the non-cytopathic CSV helper virus. Thus, exposure of day 14e-15e chick embryo bone marrow cells to REV-T (CSV) results in the generation of transformed, polyclonal lines of cells. From these lines, cells expressing cell surface immunoglobulin were readily isolated by flow cytometric cell sorting and single cell cloning. Analysis of the phenotype of REV-T(CSV)-transformed clones with a panel of monoclonal antibody reagents demonstrated that transformation by v-rel likely leads to marked changes in cell surface antigen expression. Nonetheless, clones expressing cell surface immunoglobulin expressed apparently normal mRNA for immunoglobulin mu and light chain and contained apparently normal immunoglobulin heavy and light chain gene rearrangements. Furthermore, no evidence for chromosomal deletions or aberrations of the Ig loci was detected among either sIg+ or sIg- REV-T(CSV)-transformed clones.

The v-rel oncogene of avian reticuloendotheliosis virus transforms immature and mature lymphoid cells of the B cell lineage in vitro

Heavy chain gene rearrangements were analyzed in 67 independently derived reticuloendotheliosis virus (REV-T) transformed avian lymphoid cell lines. The status of the heavy chain genes in these REV-T transformed cell lines was determined, in part, by the age of the chicken whose spleen cells were transformed. Cell lines derived by the in vitro transformation of splenic lymphocytes obtained from embryos did not contain heavy chain gene Ig rearrangements. By contrast, splenic lymphocytes transformed by REV-T obtained from birds 1 week or older generally exhibited heavy chain gene rearrangements. The REV-T transformed lymphoid cell lines with heavy chain rearrangements also had light chain gene rearrangements. The Ig gene rearrangements in REV-T transformed cells were functional. The majority of the cells which had heavy chain rearrangements expressed a 2.2-kb mu transcript and synthesized and secreted IgM. An REV-T transformant was also identified which produced IgG, suggesting that v-rel can transform a terminally differentiated cell. Irrespective of their Ig chain gene status the REV-T transformed cell lines expressed variable amounts of some but not all normal B cell-specific markers and failed to express T cell markers. All the cell lines analyzed expressed the B-L (Ia-like) antigen as well as a common leukocyte antigen. Based on the expression of these surface molecules, the transformants with or without Ig gene rearrangements all appear to be committed to the B cell pathway.

Reticuloendotheliosis virus REV-T(REV-A)-induced neoplasia: development of tumors within the T-lymphoid and myeloid lineages

Infection of 1-day-old chicks with reticuloendotheliosis virus strain T induces a neoplastic disease that kills the chicks 7 to 14 days postinfection. In association with reticuloendotheliosis-associated virus (REV-A), reticuloendotheliosis virus T (REV-T) induces tumors that are predominantly immunoglobulin M (IgM) negative. We examined a variety of REV-T(REV-A)-induced tumors and tumor-derived cell lines and concluded that the principal IgM-negative tumors that develop in REV-T(REV-A)-infected chicks are neither pre-B or pre-B-pre-T but rather mature T lymphoid and myeloid. Without exception, the immunoglobulin heavy- and light-chain loci were in germ line configuration. Furthermore, the cell lines expressed neither sterile transcripts of the heavy- or light-chain immunoglobulin genes nor elevated levels of c-myb, two characteristics associated with murine pre-B lymphomas. Cell lines were also examined by using monoclonal antibodies for expression of a variety of cell surface markers expressed on B lymphocytes and/or T lymphocytes and/or myeloid cells. These reagents defined two types of IgM-negative tumor cell lines, one CIa+ CT-3+ (T lymphoid) and the other CIa+ CT-3-. By using the same approaches, tumor development was examined following REV-T(REV-A) infection at 1 and 3 weeks post-hatching of cyclophosphamide-treated chicks shown to be devoid of B-lymphoid cells. Again, the tumors that developed were either CIa+ CT-3+ (T lymphoid) or CIa+ CT-3-. Furthermore, the frequency and rate with which IgM-negative tumors developed in cyclophosphamide-treated chicks were not different from those observed in normal chicks. In 3-week-old cyclophosphamide-treated chicks, the presence of CIa+ CT-3- tumors bearing hematopoietic lineage markers, such as CLA-3 and 5M19, are most likely to have been derived from cells within the myeloid lineage.

Markers of B lymphocyte differentiation in the chicken

A study was made of the ontogeny and tissue distribution of seven antigen systems associated with B lymphocyte development. A panel of seven monoclonal antibodies (MAbs) directed against avian bursal and peripheral B lymphocytes was developed. The spectra of cellular reactivity and size of respective antigens indicate that these MAbs appear to react with determinants of chicken B lymphocytes that had not been previously described. Immunofluorescence analysis of cell surface antigens using this panel indicated that dynamic changes in antigen expression are associated with early ontogeny and maturation of the B cell lineage. The yolk sac contained subpopulations of hematopoietic cells reactive with three MAbs (CB10, CLA3 and Hy86b5) which possibly mark the pre-bursal stem cell population. At or near the time of surface IgM expression in the embryonic bursa, B cells expressed antigens detected by the CB7, CB8, CB9 and CB11. In the juvenile chicken, CB7 reacted with immature bursal lymphocytes, while CB8, CB9 and CB10 reacted with bursal lymphocytes and a subpopulation of peripheral B lymphocytes. The antigens defined by Hy86b5 and CB11 were expressed on mature B lymphocytes but on only a subpopulation of bursal lymphocytes. The MAb CLA3 detected an antigen expressed on all leukocytes but not erythroid cells. Expression of some of these antigens by cells of the myelomonocytic lineages suggests a possible functional or ontogenetic relationship between the B lymphocyte and myeloid lineages.