Immune capacity of the chicken bursectomized at 60 hours of incubation: failure to produce immune, natural, and autoantibodies in spite of immunoglobulin production

Transfer of natural auto-antibodies via egg yolk in chickens divergently selected for natural antibodies binding keyhole limpet hemocyanin

Barcodes of natural auto-antibody (NAAb) profiles based on staining intensity of isotypes binding numbers of self-(tissue) antigen fragments were suggested as parameters for immune diversity, and related to genetic background and health status in man, rodents and poultry. Here, hens, eggs and hatchlings from chicken lines divergently selected and bred for high (H line) or low (L line) total natural antibodies (NAb) levels in plasma binding keyhole limpet hemocyanin (KLH) at 16 weeks of age were tested for their NAAb repertoire binding chicken liver homogenate (CLH) fragments using quantitative Western immunoblotting. The aims of this study were 1. to detect line differences between the H and L line adult hens, eggs and hatchlings for the IgM and IgG isotypes binding CLH fragments, 2. study the presence of NAAb of both isotypes in yolk and albumen, as well as in hatchlings to detect a maternal NAAb transfer route via the egg to the hatchling, and 3. study whether new self-antigen binding isotypes and idiotypes are present in the hatchling. NAAb binding CLH fragments were found in plasma of adult hens (both IgM and IgG), in yolk (IgG only), and hatchlings (mostly IgG, but low levels of IgM). Auto-profiles of IgM showed homogeneity, while IgG profiles were heterogenic between individual hens and individual hatchlings. Significant higher levels as indicated by staining intensity and number of stained CLH fragments were found in plasma of hens genetically selected for high levels of NAb binding KLH. Lines could be clustered based on their auto-profiles indicating that profiles of self-binding IgM and IgG antibodies are genetically based. Visual comparison, clustering and correlation of hens and their hatchlings showed similarities for the IgG, but not the IgM isotype, indicating maternal transfer of IgG NAAb via the yolk. The IgM profile in the hatchlings on the other hand might represent neonatal self-binding antibody formation. As a consequence, hatchlings initially depend for self-binding antibodies on maternal IgG provision during early life.

Maternal Transfer of Natural (Auto-) Antibodies in Chickens

The presence and relative levels (titers) of IgM and IgG natural antibodies (NAb) binding keyhole limpet hemocyanin (KLH), and natural (auto-) antibodies (N(A)Ab) binding salmon double-stranded DNA (dsDNA), (oxidated-) phosphatidyl (phosphoryl) choline-conjugated bovine serum albumin (PC-BSA), PC-conjugated ovalbumin (PC-OVA), and OVA, respectively, were studied in adult hen plasma, egg yolk, egg albumen, plasma of their hatchlings, and in 8-day-old chick plasma. Birds and eggs were from 2 lines divergently selected for high or low NAb levels binding KLH. This study aimed to determine 1) correlated phenotypic responses of selection for NAb to KLH, 2) transfer of maternal NAb and N(A)Ab via egg compartments, 3) levels of likely maternal NAb and N(A)Ab in hatchlings and 8-day-old chicks, and 4) whether a composite trait: IgM anti-PC-BSA/IgG anti-dsDNA ratio in the compartments could be used as a parameter for health or immune status. NAb and N(A)Ab to all tested antigens were found in adult hens, but low or no levels were found for IgM in yolk and IgG in albumen. Depending on the antigen, NAb and N(A)Ab were found in hatchlings and day 8 birds. Divergent selection and breeding based on NAb binding KLH affected antibody titers of almost all antigens in almost all compartments, in a similar way. Maternal transfer of NAb and N(A)Ab from the adult hen to offspring was via specific routes for specific antigens and isotypes, especially for IgG as suggested by cluster analyses and significant correlations. There was little indication of production of new NAb and N(A)Ab to the studied antigens in either the egg compartments or the hatchlings. A composite trait of IgM PC-BSA/IgG dsDNA ratio was as yet not indicative for immune status, as no significant differences were found between the lines for all compartments. In conclusion, hens provide neonatal chickens with natural (self-) binding IgG antibodies that have been proposed to perform homeostatic functions during the period in which neonates do not produce these antibodies themselves.

Local immunity of the respiratory mucosal system in chickens and turkeys

This review article presents fundamental mechanisms of the local mucosal immunity in selected regions of the respiratory tract in healthy birds and in some pathological conditions. The respiratory system, whose mucosa come into direct contact with microorganisms contaminating inhaled air, has some associated structures, such as Harderian gland (HG), conjunctive-associated lymphoid tissue (CALT) and paranasal glands (PG), whose participation in local mechanisms of the mucosal immunity has been corroborated by numerous scientific studies. The nasal mucosa, with structured clusters of lymphoid tissue (NALT - nasal-associated lymphoid tissue) is the first to come into contact with microorganisms which contaminate inhaled air. Lymphoid nodules, made up of B cells with frequently developed germinal centres (GC), surrounded by a coat of CD4+ cells, are the major NALT structures in chickens, whereas CD8+ cells are situated in the epithelium and in the lamina propria of the nasal cavity mucosa. Studies into respiratory system infections (e.g. Mycoplasma gallisepticum) have shown the reactivity of the tracheal mucosa to infection, despite a lack of essential lymphoid tissue. Bronchus-associated lymphoid tissue (BALT) takes part in bronchial immune processes and its structure, topography and ability to perform defensive function in birds is largely age-dependent. Mature BALT is covered by a delicate layer of epithelial cells, called follicle-associated epithelium (FAE). Germinal centres (GC), surrounded by CD4+ cells are developed in most mature BALT nodules, while CD8+ lymphocytes are dispersed among lymphoid nodules and in the epithelium, and they are rarely present in GC. Macrophages make up the first line of defence mechanisms through which the host rapidly responds to microorganisms and their products in the respiratory mucosal system. Another very important element are polymorphonuclear cells, with heterophils being the most important of them. Phagocytic cells obtained from lung lavages in birds are referred to as FARM (free avian respiratory macrophages). Their number in chickens and turkeys is estimated to be 20 times lower than that in mice and rats, which indicates a deficit in the first-line of defence in the birds' respiratory system. There are numerous B cells and antibody secreting cells (ASC) present throughout the respiratory system in birds. Their role comes down to perform antigen-specific protection by producing antibodies (IgM, IgY or IgA class) as a result of contact with pathogenic factors.

Natural antibodies in bovine milk and blood plasma: variability among cows, repeatability within cows, and relation between milk and plasma titers

Innate immunity plays an important role in preventing (barrier function) or combating infection (effector function). An important humoral component of innate immunity is formed by natural antibodies (NAb). The objectives of this study were to determine presence, variation among cows and repeatability within cows over time of total NAb titers directed to the pathogen-associated molecular patterns lipopolysaccharide, lipoteichoic acid (LTA) and peptidoglycan, and titers of NAb directed to the glycoprotein keyhole limpet hemocyanin in milk and plasma of individual cows. Furthermore in milk the antibody isotypes IgG1, IgG2, IgM and IgA binding LTA were analyzed. Ten milk and blood samples were obtained from each of 20 clinically healthy dairy cows from first to seventh parity during a period of 3 weeks. Total NAb binding lipopolysaccharide, LTA, peptidoglycan, and keyhole limpet hemocyanin were detected in milk and plasma, with titers considerably higher in plasma than in milk. Total NAb titers showed significant variation among cows, and repeatability within cows over time (ranging from 0.60 to 0.93). Titers of NAb in milk and plasma were positively correlated (correlation ranging from 0.69 to 0.91). Natural antibodies in milk binding LTA were of all 4 isotypes tested, although IgG2 was on average only present at low titers. All 4 isotypes in milk binding LTA also showed variation among cows, and repeatability within cows over time (ranging from 0.84 to 0.92). We conclude that NAb can be measured in a consistent and repeatable manner in bovine milk and blood plasma.

Decreased specific antibody responses to alpha-Gal-conjugated antigen in animals with preexisting high levels of natural antibodies binding alpha-Gal residues

High levels of natural antibodies (NAb) binding the alpha-Gal residue (Galalpha1-3Galbeta1-4GlcNAc) are found in poultry (and humans), which is probably reflected by high levels of natural agglutinating antibodies (Ab) to rabbit red blood cells (RRBC) in plasma from chickens (and humans). Recently, it was shown that alpha-Gal conjugation of proteins induced higher antiprotein Ab responses in alpha-Gal knockout mice, suggesting immune-enhancing features of preexisting Ab binding carbohydrate-protein conjugates. We challenged chickens s.c. with either alpha-Gal-conjugated human serum albumin (HuSA), beta-Gal-conjugated HuSA, or unconjugated ("native") HuSA, respectively, and measured primary and secondary Ab responses to HuSA, including isotype IgM and IgG responses, and cellular immune responses in vitro (lymphoproliferation) to HuSA or concanavalin A. alpha-Gal conjugation, but not beta-Gal conjugation, of HuSA resulted in significantly decreased primary and secondary Ab responses to HuSA, especially IgG isotype responses, as compared with Ab responses to native HuSA. Lymphoproliferation in vitro was also decreased, although not significantly, in birds challenged with alpha-Gal-conjugated HuSA. High levels of agglutinating Ab levels to RRBC and NAb binding porcine thyroglobulin were detected in all birds, as was true for (natural) Ab levels binding alpha-Gal-conjugated HuSA before immunization, whereas low levels of preexisting (natural) antibodies directed to native HuSA were present in plasma before immunization. Levels of RRBC agglutinins and Ab binding thyroglobulin were not affected by immunization with HuSA, alpha-Gal-conjugated HuSA, or beta-Gal-conjugated HuSA. Our data confirm the presence of high levels of (preexisting) NAb in the plasma of chickens directed to the alpha-Gal residue. The decreased responsiveness to alpha-Gal-bearing antigens in the current study shows that, in addition to immune-enhancing features, NAb may also have suppressive effects on specific immune responses, which substantiates the regulatory role of innate immunity (NAb) in mounting specific immune responses.

Detection of QTL for innate: non-specific antibody levels binding LPS and LTA in two independent populations of laying hens

In the current study results are presented of an experiment dealing with the Natural antibodies which are measured by level of homotopes LPS and LTA. Two independent populations were examined (F2 population descendant from a cross between chickens divergently selected for either High or Low specific Ab responses to SRBC (HL) and F2 cross descendant from lines expressed different behavior concerning feather pecking (FP)). In total 12 QTL were detected to non-specific antibody titers directed to LTA and LPS and at two ages after applying two statistical models in an F2 HL population. Similarly in an FP cross overall seven QTL were detected. Based on obtained results it might be concluded that different QTL regions are associated with immune responses to homotopes LPS and LTA in poultry.

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.

The avian B-cell receptor complex: distinct roles of Igalpha and Igbeta in B-cell development

The bursa of Fabricius has evolved in birds as a gut-associated site of B-cell lymphopoiesis that is segregated from the development of other hematopoietic lineages. Despite differences in the developmental progression of chicken as compared to murine B-cell lymphopoiesis, cell-surface immunoglobulin (sIg) expression has been conserved in birds as an essential checkpoint in B-cell development. B-cell precursors that express an sIg complex that includes the evolutionarily conserved Igalpha/beta heterodimer colonize lymphoid follicles in the bursa, whereas B-cell precursors that fail to express sIg due to non-productive V(D)J recombination are eliminated. Productive retroviral gene transfer has allowed us to introduce chimeric receptor constructs into developing B-cell precursors in vivo. Chimeric proteins comprising the extracellular and transmembrane regions of murine CD8alpha fused to the cytoplasmic domain of chicken Igalpha efficiently supported B-cell development in precursors that lacked endogenous sIg expression. By contrast, expression of an equivalent chimeric receptor containing the cytoplasmic domain of Igbeta actively inhibited B-cell development. Consequently, the cytoplasmic domains of Igalpha and Igbeta play functionally distinct roles in chicken B-cell development.

Adoptive transfer of natural antibodies to non-immunized chickens affects subsequent antigen-specific humoral and cellular immune responses

To determine a regulatory function of natural antibodies in the immune response of chickens, pooled plasma obtained from non-immunized (naïve) 15 months old hens was subjected to keyhole limpet hemocyanin (KLH) antigen-affinity chromatography. Purified KLH-binding antibodies were adoptively transferred intravenously to 5 weeks-old cocks that were subsequently immunized subcutaneously 24 h later with KLH. Control groups consisted of birds that were either adoptively transferred with KLH-binding antibodies purified from plasma of KLH-immunized chickens, or PBS, or a salt precipitated total immunoglobulin fraction obtained from the corresponding pooled nai;ve chicken plasma, respectively.Total, IgM and IgY antibody titers to KLH in the plasma of recipients adoptively transferred with KLH-NAb, but not in the plasma of the groups transferred with salt precipitate or KLH-binding specific antibodies, were significantly enhanced as compared to the non-treated, KLH immunized group. Titers of IgA antibodies binding KLH were decreased in the plasma of the group that received specific KLH-binding antibodies, but not in the plasma of the other groups. Proliferation from peripheral blood leucocytes in whole blood from the KLH-NAb treated group, the group treated with KLH-binding specific antibodies and the group treated with salt precipitate, respectively, to both concanavalin A and KLH were significantly decreased as compared to the group receiving PBS. Our data show that antigen-specific antibodies can be isolated from plasma obtained from non-immunized chickens. Such antibodies that resemble natural antibodies as described in mammals may perform an important role in the enhancement of subsequent antigen-specific antibody responses or the maturation of the immune system, which may differ from the role of specific antibodies.

Different levels of natural antibodies in chickens divergently selected for specific antibody responses

We studied the presence of Natural antibodies in plasma samples from individual birds from selected chicken lines at young and old age. Binding, specificity, and relative affinity to various antigens were determined in plasma from non-immunized female chickens at 5 weeks of age, and in plasma obtained from the same chickens one year later using indirect two-step ELISA. Birds were from three different lines. The lines were divergently selected for either high (H line) or low (L line) antibody titers to Sheep Red Blood Cells at 5 weeks of age, next to a random bred control (C line). Binding of plasma immunoglobulins (Ig) from all three lines was found with chicken-egg-white protein (CEP), ovalbumin (OVA), myoglobin (MYO), thyroglobulin (THYRO), keyhole limpet hemocyanin (KLH), bovine serum albumin (BSA), and transferrin (TRANS). Significantly higher binding to most antigens was found with plasma Ig from adult birds from the H line as compared to plasma Ig from the L line, whereas binding of plasma Ig from C-line birds was in between or similar to the H or L line, respectively. Binding of Ig to all antigens in all three lines was significantly higher in plasma obtained at one year of age as compared to plasma obtained at 5 weeks of age. A competitive ELISA with homologous and heterologous antigens was used for determining specificity of the antigen-binding antibodies. Nai;ve plasma samples were characterized by a broad binding to all antigens tested. Inhibition of binding to specific antigens was possible with a broad range of heterologous antigens, but highest competition of binding was obtained with homologous antigen. Both linear regression analysis of serial dilutions of the plasma Ig binding the antigens, as well as competitive ELISA with homologous antigen indicated that plasma Ig from the H line and plasma Ig from the L line had similar affinity characteristics to the antigens tested with the exception of OVA and KLH. Pooled non-immune plasma from H line birds bound to CEP, OVA, THYRO, TRANS, MYO, KLH, and salt-precipitated extracts and supernatants of extracts from chicken heart, spleen, liver, brain, bursa, thymus, and kidney, respectively, as determined by Western blotting. The increasing presence of antibodies in nai;ve chicken plasma binding heterologous and homologous (tissue) antigens indicates the presence of Natural antibodies in poultry. Apart from age, increasing levels of Natural antibodies may be related with the genetically based magnitude of specific antibody levels in the chicken lines studied.

Diversity in the CDR3 region of V(H) is sufficient for most antibody specificities

All rearranging antigen receptor genes have one or two highly diverse complementarity determining regions (CDRs) among the six that typically form the ligand binding surface. We report here that, in the case of antibodies, diversity at one of these regions, CDR3 of the V(H) domain, is sufficient to permit otherwise identical IgM molecules to distinguish between a variety of hapten and protein antigens. Furthermore, we find that somatic mutation can allow such antibodies to achieve surprisingly high affinities. These results are consistent with a model in which the highly diverse CDR3 loops are the key determinant of specificity in antigen recognition in both T cell receptors (TCR) and antibodies, whereas the germline-encoded CDR1 and CDR2 sequences are much more cross-reactive.

Avian B cell development

Development of B cells in chickens proceeds via a series of discrete developmental stages that includes the maturation of committed B cell progenitors in the specialized microenvironment of the bursa of Fabricius. The bursa has been shown to be required for the amplification of the B cell pool and selects for cells with productive immunoglobulin rearrangement events. Other events regulating chicken B cell development such as lymphocyte trafficking and apoptosis are just beginning to be elucidated. Within the bursa, the variable regions of immunoglobulin genes of B cell progenitors are diversified by a process of intrachromosomal gene conversion, where blocks of sequence information are transferred from pseudo-V regions to the recombined variable regions of the immunoglobulin genes. Recently gene conversion has been determined to play a role in the diversification of the immune repertoire in other species. In this review we focus on the current understanding and recent advances of B cell development in the chicken.

Current concepts in chicken B cell development

The chicken has provided fundamental insights into the workings of vertebrate immunity. In particular, the development of B cells in a unique organ, the bursa of Fabricius, has provided a novel opportunity to study B cell development. Although chickens generate their Ig repertoire in a different way than mice and humans, there are many striking similarities in the developmental process. In particular, the control of lymphocyte migration and survival is key to the development of an immune system. The evolutionary distance of chickens and mammals underscore how common the problems are as well as how the solutions are often similar. Such commonalities serve to maintain the chicken as a compelling animal in which to study B cell development.

Embryogenesis of the bursa of Fabricius: stem cell, microenvironment, and receptor-paracrine pathways

The bursa of Fabricius is an ideal model system to answer the plethora of questions related to the origin of B cells and microenvironmental issues leading to the education of the stem cell. Prior to the 1960s, lymphocytes were thought to be derived from epithelial or mesenchymal cells. Later work demonstrated the bloodborne nature of the stem cell contributing to B cells. Stem cells entered the bursa of quail and chicken between 7 and 11 and 7.5 and 14 d of embryogenesis, respectively. Interspecific chimeric studies, quail and chick, emphasized the intraembryonic origin and sites of the stem cell. The bloodborne and stromal cells that contribute to the microenvironment of the bursa orchestrate the events leading to B cell differentiation. The separation of the endodermal and mesodermal components of the bursa revealed a singular role for the endoderm in the genesis of the bursa but did not exclude a role for the mesoderm. A dark mesenchymal cell was shown to play a role in bud formation. This cell gave rise to the bursal secretory dendritic cell (BSDC), unique in its membrane association with IgG. A receptor-paracrine thesis has been proposed to explain the interaction between in-frame B cells and Ig-positive BSDC in the expansion of in-frame B cells and the subsequent development of the B cell repertoire. Cell adhesion molecules have been integrated into this thesis.

The bursa of Fabricius: the evolution of a discovery

It has been a joy these past 40 yr to have traveled the "Bursal Road"--a road we helped construct and whose route allowed us to make a variety of observations that contributed either to basic science or indirectly or directly to the role of the bursa of Fabricius in the B cell repertoire. The chicken's bursa of Fabricius introduced me to endocrine, heritability, and growth studies, which allowed serendipity to occur and the revelation of the classical and modification of the classical theses of bursal function. The modification of the classical thesis, presence of immunoglobulin in the absence of the bursa, raised questions that directed us to study hypothalamic control of behavior, which was not directly related to bursal function. This forced us to learn various techniques, e.g., autoradiography, cell labeling, and electron microscopy, that made it possible to study long- and short-lived lymphocytes, lymphokines, labeled cells, and the fine structure and function of the bursa of Fabricius, cecal tonsil, Harderian gland, lymph nodes, Meckel's diverticulum, Pineal gland, and spleen. In an attempt to use cyclophosphamide to understand how the spleen acquired the ability to produce antibodies, we revealed a dendritic cell in the bursa, the bursal-secretory dendritic cell (BSDC), and in the spleen, the ellipsoid-associated cell (EAC). The BSDC is a novel cell in the bursal microenvironment and may be involved in an interaction with prebursal or bursal stem cells, leading to the differentiation or selection of the B cell repertoire of the chicken.

Stochastic rearrangement of immunoglobulin variable-region genes in chicken B-cell development

The molecular mechanism by which immunoglobulin (Ig) gene rearrangement occurs is highly conserved between mammalian and avian species. However, in avian species, an equivalent to the mammalian pre-B cell, which has undergone Ig heavy-chain gene rearrangement and expresses mu heavy chains in the absence of Ig light-chain rearrangement, has not been convincingly demonstrated. It is consequently unclear whether an ordered progression of gene rearrangement events leading to functional Ig expression occurs in avian species. To examine the sequence of Ig gene rearrangement events in chicken B-cell development, we transformed day 12 embryo bursal cells with the REV-T(CSV) retrovirus. More than 100 clones were analyzed by Southern blotting and polymerase chain reaction for the presence of Ig gene rearrangements. The majority of these clones contained only germline Ig sequences. Several clones contained complete heavy- and light-chain rearrangements and 13 clones contained only heavy-chain rearrangements analogous to stages of mammalian B-cell development. However, 5 clones contained rearrangements of light-chain genes in the absence of complete heavy-chain rearrangement. Consequently, we conclude that rearrangement of chicken Ig light-chain genes does not require heavy-chain variable-region rearrangement. This observation suggests that chicken Ig gene rearrangement events required for Ig expression occur stochastically rather than sequentially.

Historical perspective: the bursa of Fabricius and its influence on B-cell development, past and present

The bursa of Fabricius has a history and a future. The history included its description by Hieronymus Fabricius and the discovery in the 1950s of its pivotal role in humoral immunity. The apparent obligate role of the bursa in B-cell development was modified by research in the 1960s and 1970s which described the synthesis of immunoglobulin in bursaless birds and led to the concept of extra bursal sites. Then in the 1980s, supported by the research of the past 25 years and the new technology, the obligate role of the bursa in orchestrating the V-gene repertoire-antibody diversity was revealed. Microenvironmental studies in the 1970s and 1980s announced the importance of bursal epithelium, secretory dendritic cells, and other reticuloepithelial cells in interpreting the ontogeny of B-cell differentiation. The past history of the bursa will be remembered for its contribution to present and future research and the present and future will be promising if the experiences of the past are not forgotten.

Effect of surgical and chemical in ovo bursectomy on lymphocyte density scores and histological evaluations of primary and secondary lymphoid organs in hypertensive and hypotensive turkeys

The effects of surgical and chemical in ovo bursectomy on the histology of primary and secondary lymphoid organs were studied in hypertensive and hypotensive lines of turkeys. The effects of bursectomy were measured by determining the presence of lymphatic nodules and the presence of lymphocytes in secondary lymphoid organs: spleen, cecal tonsil, Meckel's diverticulum, and Peyer's patches; as well as in the thymus and bursa of Fabricius. No treatment effect on splenic nodule formation occurred, but a significantly lower lymphocyte density score was present in the surgically bursectomized group. Both nodule formation and lymphocyte density scores for the cecal tonsil and Peyer's patches were significantly reduced in the surgically bursectomized and testosterone-treated groups as compared with the control and sham groups. The most consistent depression in lymphatic scores in both the surgically and chemically bursectomized groups occurred in the Peyer's patches followed by cecal tonsils and Meckel's diverticulum. As expected, there were no differences in thymocyte density scores. There was no consistent effect on lymphatic scores due to blood pressure selection; however, the hypertensive line showed significantly lower scores than the hypotensive line in the bursa, cecal tonsils, and Peyer's patches. No differences between the sexes were noted in any organ.

Suppression of chicken J chain production by in ovo bursectomy

The influence of in ovo bursectomy on the levels of J and mu chains in the sera of embryonic and hatched chicks was studied by the dot blotting immunoassay. The results indicated a decrease in the level of J chains during the embryonic stage after treatment with testosterone compared with normal chicks. Testosterone treatment caused a decrease in J-chain levels after hatching which was more marked in reduced-alkylated than in non-reduced sera. In contrast, testosterone caused no significant change in serum levels of mu chains, either in ovo or after hatching. Our findings further present the paradox that although removal of the bursa of Fabricius by testosterone treatment did not impair mu-chain synthesis, B-cell differentiation was suppressed. These observations indicate that in ovo bursectomy selectively inactivates B-cell differentiation as indicated by the induction of immunodeficiency, and results in the failure of J-chain production.

Chicken IgL variable region gene conversions display pseudogene donor preference and 5' to 3' polarity

Chicken immunoglobulin variable region diversity is generated during B-cell development in the bursa of Fabricius by intrachromosomal gene conversion, resulting in the replacement of sequence blocks within the unique rearranged VL1 and VH1 genes with homologous sequences derived from V region pseudogene segments (psi V). In this report, the nucleotide sequences of 217 gene conversion events in 52 random IgL clones were analyzed to characterize the molecular mechanism of gene conversion. The frequency of psi VL usage as gene conversion donors is shown to depend on the proximity of the psi VL segment to VL1, extent of homology with VL1, and relative orientation of the psi VL segments. Gene conversion events are not observed in the 5' region of homology between psi VL segments and VL1, but are distributed throughout the remainder of the VL1 exon. The 5' ends of individual gene conversion events always begin in regions of homology between the donor psi VL and recipient VL1 gene, whereas the 3' ends can occur in regions of nonhomology and often have nucleotide insertions or deletions. These results suggest a 5' to 3' polarity in the gene conversion mechanism. The implications of our data are discussed in relation to current molecular models of gene conversion.

Effects of gender and sex steroids on the immune response

Elevated immune responses and the higher incidence of autoimmune diseases in female (compared to male) humans and animals have been known for a long time. However, the scientific interest in this interrelationship has been limited both amongst immunologists and endocrinologists. It is mainly in the last ten years that investigations in this area have been intensifying. A number of fairly recent review articles confirm the increased interest in various aspects of this "interdiscipline" [1-4]. In the present paper we should like to make a new assessment of the state of knowledge. We shall firstly discuss heteroimmune response differences between males and females in humans, rodents and birds and then the roles of gender and sex hormones in autoimmune disease in various species. The general conclusions are the following. Gender and sex hormones have a clear effect on various hetero- and auto-immune responses but the mechanisms of action are still unknown; starting from sex hormones, steroids can be devised which have favourable effects on immune processes but lack undesirable hormonal effects; such hormonomimetics should be, in principle, applicable for the treatment of autoimmune disease.

Somatic diversification of the chicken immunoglobulin light-chain gene

The bursa of Fabricius provides a unique organ for the study of lineage-specific development in a multicellular organism. Unlike mammalian B cells, B cells in the chicken develop in a single wave of differentiation, beginning with the commitment of progenitor cells to the B cell lineage between days 10 and 15 of embryogenesis. By day 18 of embryogenesis, all lymphoid progenitor cells capable of differentiation along the B cell lineage have migrated to the bursa of Fabricius. Following migration to the bursa, these lymphoid progenitors enter exponential growth and begin to populate each of the 10(4) bursal follicles. Between day 18 of embryogenesis and 2-4 weeks of age, B cells undergo a stage of bursal-dependent differentiation. By the end of this period, chickens are able to mount primary immune responses against virtually all antigens. In addition, by this time sufficient numbers of B cells have migrated from the bursa to peripheral lymphoid organs so that the B cell immune system can be maintained even if the bird is bursectomized. Bursectomy of chicks after 4 weeks of age has no long-term effects on the development and maintenance of the B cell immune system in adult birds. Because of the central nature of the surface Ig molecule to B cell development in mammals, the chicken IgL gene locus has been intensively studied during avian B cell development. The chicken IgL locus is a particular interest because it has only one V region capable of rearrangement. Rearrangement of the IgL gene is not dependent on the bursal environment. B cell progenitors rearrange their IgL gene between days 10-15 of embryogenesis, prior to migration to the bursa. IgL gene rearrangement occurs by a deletional mechanism in which a precise joining of the IgL recombination signal sequences leads to a circular episomal element. During this deletion it appears that single nonrandom bases are added to both the V and J coding segments. Subsequent V-J joining occurs at random. Most progenitor B cells appear to rearrange only a single IgL allele. The high frequency of in-frame alleles observed in avian B cell lines appears to result from the selective amplification of cells with productive IgL rearrangements during bursal development between days 12 and 18 of embryogenesis. To create an immunological repertoire, chickens must diversify the coding sequence of this single functional V gene segment during development.(ABSTRACT TRUNCATED AT 400 WORDS)

B-cell differentiation in the chicken: expression of immunoglobulin genes in the bursal and peripheral lymphocytes

We have studied the expression of immunoglobulin genes in the chicken B-cell precursors, and of a B-cell surface marker (Bu-1) on the bursal and peripheral B cells during normal ontogeny. Since there is no way of distinguishing the precursor cells from the more mature bursal lymphocytes on the basis of surface markers, we chose to study the total bursal lymphocyte population at ages when the numbers of the various precursor cells (bursal, early post-bursal, and post-bursal stem cells) in the bursa are estimated to be at their highest. Thereafter, comparisons with the more mature lymphocytes in the peripheral organs were made. As a result, levels of the lambda and mu transcripts and expression of Bu-1 antigen in the chicken B-cell precursors were found to be unchanged during the post-hatching period. In the light of these experiments, the later events of B-cell differentiation, i.e. the development from the bursal to post-bursal B lymphocytes, occurs without the lambda, mu, and Bu-1 gene loci involved. On the other hand, the higher level of lambda and mu expression in the splenic B lymphocytes indicates that the post-bursal stem cells mature into highly active plasma cells after seeding to the peripheral organs.

Antibody-forming capacity of B cell-deficient chickens reconstituted with limiting numbers of B cell precursors

To examine the antibody-forming capacity of neonatally cyclophosphamide-treated chickens reconstituted with limiting numbers of B cell precursors, we analyzed their antibody responses to six unrelated antigens. Our results demonstrate that about 10 x 10(6) bursal cells are needed in this adoptive cell transfer model to restore normal immune competence to B cell-deficient birds. From our earlier data we know that with low repopulating cell numbers (less than 10 x 10(6) cells) developing bursal follicles are of clonal origin. Ten million cells repopulate about 40%, i.e. about 4 x 10(3) of the bursal lymphoid follicles. Assuming the clonal origin of the follicles these results imply that the B cell system of birds receiving this dose is derived from less than 5 x 10(3) precursor cells. At the lowest reconstituting dose (1.25 x 10(6) cells) most birds do not respond to the antigens studied. However, their B cell system is derived from only about 500 precursor cells. Because the antibody repertoire of a normal chicken was estimated to be at least 10(6) our results suggest that each precursor gives rise to a large number (greater than 200) of immunoglobulin V-region gene variants during its clonal proliferation in the bursa. Our results are thus consistent with the proposed "hyperconversion" mechanism of generation of antibody diversity in the chicken and provide quantitative data useful for estimating what such somatic modification rates might be.

Effects of steroids with different endocrine profiles on the development, morphology and function of the bursa of Fabricius in chickens

This paper describes the effect of various steroids on the anlage of the bursa of Fabricius in chickens. The steroids were administered by dipping embryonated eggs on the third day of incubation in ethanolic solutions of these steroids. The results with about 30 different steroids show that the capacity to inhibit the development of the bursa does not correlate with the endocrine properties of these steroids as measured in routine screening tests for androgenic, anabolic, progestational and oestrogenic activities or with the relative binding affinities for various endocrine receptors. More elaborate studies with several representative steroids show that testosterone (10 mg/ml), nandrolone (10 mg/ml), 11 alpha-hydroxynandrolone (10 mg/ml), ethylestrenol (1 mg/ml), lynestrenol (1 mg/ml), and Org OD14 [tibolone] (0.1 mg/ml) induce also histomorphological changes in the remaining bursa tissue still present in 10 day- and 53-day old chickens and in the bursa-dependent sites of their spleens (53-day old chickens only). Testosterone and lynestrenol induced smaller changes than nandrolone or ethylestrenol. Tibolone and 11 alpha-hydroxynandrolone were more effective than nandrolone. All drugs, except testosterone and lynestrenol, imparied antibody formation to Newcastle Disease Virus and decreased the serum levels of total IgG, but not of total IgM. Also these effects were not correlated with endocrine properties. In other studies (for references, see text) we found that several of these steroids, notably tibolone, favourably influence the course of spontaneous autoimmune diseases of NZB/W mice and Obese Strain chickens. Since this autoimmunosuppression is likely to be caused by inhibitory effects on bursa or bursa equivalent, we may use this approach for developing medically useful autoimmunosuppressive steroids with minimal endocrine effects.

Avian B cell precursors: surface immunoglobulin expression is an early, possibly bursa-independent event

The avian bursa of Fabricius contains about 1 X 10(4) discrete follicles, each of which is colonized by a small number of lymphoid progenitor cells during embryonic life. We have previously shown (J.R.L. Pink et al., Eur. J. Immunol. 1985. 15:617) that all, or almost all B cell progenitors in the bursae of 4-day-old chicks express cell surface IgM. In this report, we have analyzed the distribution of cell surface (s)IgM-1 allotypes within individual follicles of (M-1a/M-1b) allotype heterozygous birds. Although the majority of follicles contained a mixture of sIgM-1a+ and sIgM-1b+ cells, a significant proportion of isolated follicles contained exclusively sIgM-1a+ or sIgM-1b+ cells. Statistical analysis of the frequency of such "M-1a" and "M-1b" follicles demonstrated that the sIg+ B cells in the bursae of 4-8-week-old birds are derived from 2-4 allotypically committed precursor cells per follicle. Since we have previously shown that each bursal follicle is colonized by 2-5 pre-bursal stem cells, these cells must be committed to the eventual expression of one or other allotypic haplotype before they have undergone extensive proliferation within the bursa. In addition, we show that almost all B progenitor cells from the bursae of chicks which had been allotype suppressed as embryos were committed to synthesis of the nonsuppressed allotype, showing that this commitment was essentially complete at the time of suppression (i.e. before 19 days of incubation). Finally the bone marrow of 16-day embryos was used to reconstitute the bursal lymphocytes of cyclophosphamide-treated host embryos. Reconstitution was inhibited by anti-Ig antiserum indicating that most 16-day embryonic BM-derived bursal cell precursors also express sIgM. These results raise the possibility that expression of sIgM may be controlled by a "biological clock" rather than by any inductive capacity of the bursal microenvironment. Furthermore, these results provide further evidence that in normal birds a self-renewing sIg+ B cell population in the hatched chicken is the sole source of B cells in the adult.

Defect in the generation of light-chain diversity in bursectomized chickens

The avian bursa of Fabricius has been regarded as a central organ for B-cell development, but there is controversy about the existence of other sites for differentiation of B cells. We have recently shown that chickens surgically bursectomized as early embryos, before the bursal primordium appears, can produce cytoplasmic, surface and serum immunoglobulins of IgM, IgG and IgA classes but are unable to generate specific antibodies in response to antigen. We have therefore examined the structure and diversity of immunoglobulins of bursectomized chickens. Analysis of serum IgG revealed normal gamma-heavy chains but altered light chains with more basic and less diverse isoelectric points than normal. These light chains may represent germ-line specificities not diversified by somatic mutations. Thus the bursa of Fabricius appears not to be necessary for the production of immunoglobulin molecules as such but to function in the creation and expansion of the antibody repertoire, possibly by providing a microenvironment for somatic mutations.

Ontogeny of primary lymphoid organs and lymphoid stem cells

Cells of the immune system go through a series of important developmental steps that begin early in embryonic life and include, first, the various waves of hemopoietic-cell production in the embryo and, second, the homing of these cells to the hemopoietic organs, which are the sites of hemopoiesis and lymphopoiesis in embryonic and adult life. The avian embryo is an important model for investigating these early steps; and this paper presents a comprehensive review of the work done on the early ontogeny of the avian immune system.

Immune capacity of the chicken bursectomized at 60 H of incubation. Effect of bursal epithelial cells and bursal epithelium-conditioned medium on the production of immunoglobulins and specific antibodies in vitro

Cells from chickens bursectomized at 60 h of incubation (Bx) are known to produce immunoglobulins without any detectable antibody specificity. In the present work cells from Bx birds were cultured together with bursal epithelial cells (BE) or bursal epithelium-conditioned medium (BECM) to establish whether they could be induced to produce specific antibodies. Cells obtained from 10-day-old or 10-week-old birds were used. The effects were assessed with regard to the production of total immunoglobulins and specific antibodies; the birds had been preimmunized. BE had no effect on the production of immunoglobulins by either Bx or control (Co) cells. When cells from 10-week-old birds were cultured in the presence of BECM, no difference in the immunoglobulin production was seen between Bx and Co chicken cells. At the age of 10 days the cells of Bx birds produced considerably less Ig than the cells of normal Co birds. At this age BECM had no effect on the Co cells, but it markedly enhanced the production of IgA-class immunoglobulins of Bx birds. With regard to production of specific anti-tetanus antibodies, BE stimulated the production of IgA-class antibodies by cells from preimmunized Co chickens but had no effect on cells from preimmunized Bx birds. In spite of the normal production of immunoglobulins in vitro the cells of Bx chickens did not produce specific antibodies. In conclusion, these findings indicate that if B cells have matured without a contact with the bursa of Fabricius, later in vitro exposure to BE or BECM can no longer induce them to production of specific antibodies.

Immune capacity of the chicken bursectomized at 60 hr of incubation: effect of adherent cells on the production of immunoglobulins and specific antibodies in vitro

Cells from chickens bursectomized at 60 hr of incubation (Bx) and normal controls (Co) were assessed for the ability to secrete immunoglobulins and specific antibodies in vitro. Anti-tetanus antibodies were observed in the culture supernatants of cells from tetanus-immunized Co chickens. Cells from immunized Bx and nonimmunized Co chickens did not secrete specific antibodies. Cells of both Bx and Co chickens secreted similar amounts of immunoglobulins (IgM, IgG, IgA). Antigenic stimulation in vitro had no effect on the secretion of specific antibodies or on cell proliferation; this applies for Bx and Co chickens. To test whether antigenic stimulation in vitro together with adherent cells would induce antibody production in Bx cells, cocultures of peripheral blood adherent cells and lymphocytes from spleen or peripheral blood were used. Culture of lymphocytes with histocompatible and allogeneic adherent cells, with or without antigenic stimulation, did not enhance secretion of anti-tetanus antibodies from cells of Bx chickens. The adherent cells increased the secretion of total immunoglobulins, of all classes, by both Co and Bx cells alike. They also enhanced the secretion of specific antibodies by Co cells. These findings indicate that the functional failure of Bx lymphoid cells cannot be corrected by better antigenic presentation.