Genetic control of immune responses in chickens: I. Responses to a terpolymer of poly(Glu60Ala30Tyr10) associated with the major histocompatibility complex

Genetic and other effects on antibody and cell mediated immune response in swine leucocyte antigen (SLA)-defined miniature pigs

Miniature pigs of eight swine leucocyte antigens (SLA) haplotypes were immunized with sheep erythrocytes (SRBC), hen egg white lysozyme (HEWL) and the synthetic peptide (T, G)-A--L to induce antibody. Bacillus Calmette Geurin (BCG) and dinitrochlorobenzene (DNCB) were used to induce cell mediated immune response (CMI). Analysis of variance by least squares was used to assess the effects of SLA haplotype, sire, dam, litter and sex of pig on the magnitude of the primary and secondary antibody response and on dermal delayed type hypersensitivity induced by purified protein derivative of tuberculin (PPD) and DNCB-induced contact hypersensitivity. The statistical model accounted for 43.50-77.30% of the observed variability in antibody and CMI at various times after immunization or challenge. While SLA had a significant effect on both antibody and CMI to some antigens at some, but not all times, sire, dam and litter were more frequently significant and to a greater degree. Haplotypes dd, dg and gg produced more antibody to SRBC and (T, G)-A--L while dg and gg had higher primary, but not secondary antibody response to HEWL. Delayed hypersensitivity to PPD was most marked in pigs of dd, dg and gg haplotypes while contact hypersensitivity to DNCB was expressed least in the dg and gg haplotype pigs. Heritability estimates were high for response to (T, G)-A--L and HEWL indicating feasibility of selective breeding for these traits.

Genetic variation in major histocompatibility complex class I alpha2 gene among broilers divergently selected for high or low early antibody response to Escherichia coli

The MHC genes have a profound effect on animal abilities to respond to specific antigens because they play a role in presenting foreign antigens to T cells during the course of the humoral or cellular immune response. In the current study, polymorphism in the MHC class I alpha2 domain was compared in 2 lines divergently selected for high (HH) or low (LL) antibody response to Escherichia coli vaccine. These lines also differ markedly in their antibody response to natural E. coli exposure and to vaccination with Newcastle disease virus, infectious bronchitis virus, and infectious bursa disease virus. Recent trials have shown that the LL chicks exhibit a significantly higher percentage of CD8+ T lymphocytes in their peripheral blood lymphocytes and spleen than HH chicks. Despite symmetrical selection intensity in both lines, polymorphism of the alpha2-domain gene was higher in the LL line than in the HH line. Among 29 single-nucleotide polymorphism positions found, 3 were unique to the HH line, 15 were unique to the LL line, and 11 were polymorphic in both lines. These single nucleotide polymorphism positions were not 100% line specific and were in agreement with the genetic variation in antibody level or cellular response still found within the selection lines. Five amino acid positions showed significant differences in polymorphism between the selection lines. These were located within the antigen-binding cleft, suggesting that these positions might influence the ability of MHC class I to bind foreign antigens and leading to differences in immunocompetence between the lines.

Alloantigen systems L and P influence phagocytic function independent of the major histocompatability complex (B) in chickens

Synthetic parent stocks were designed to produce progeny among which alleles were simultaneously segregating for nine alloantigen systems, including the MHC (B). Chicks from Ancona-derived B19B19 females crossed with White leghorn B19B21 males were blood typed, resulting in genotypic categories for the A-E, C, D, H, I, L, and P loci with the objective of determining which, if any, of the eight non-MHC alloantigen systems influence or interact with the B system genotypes for blood monocyte phagocytic activity. Leukocytes obtained from whole blood at 2 and 4 wk were separated on a Fico/Lite LymphoH, density gradient and were allowed to adhere to glass coverslips. The resulting adherent monocyte monolayers were incubated with viable Escherichia coli for 1 h and stained with Leukostat, and the phagocytic monocytes and numbers of internalized bacteria per phagocytic monocyte were scored microscopically. The combined results from two separate trials demonstrated that the genotypes of the A-E, C, D, H, and I systems did not differ in the percentage of monocytes exhibiting phagocytosis, whereas significant differences were noted relative to the B system genotype at 2 wk of age (B19B21 > B19B19; P = 0.049), L at 4 wk (L1L1 > L1L2; P = 0.009), and P at 4 wk (P4P4 > P1P1; P = 0.047). The data were further analyzed to determine any interactions of P and L alloantigen genotypes with the B system genotypes; no such interaction was observed. These studies suggest that the L and P non-MHC alloantigen systems have the potential to influence immune responses by modulating phagocytic function in chickens. Furthermore, this modulation seems to be independent of the B (MHC) system.

Analysis of MHC class II and class IV restriction fragment length polymorphism in chicken lines divergently selected for multitrait immune response

In the present study, chickens of four lines divergently selected for high (H) and low (L) immunocompetence in replicate were analyzed to investigate polymorphisms of MHC class II and MHC class IV on the molecular level associated with selection. The long-term selection experiment for multitrait immunocompetence was carried out in replicates and allows, therefore, the opportunity to distinguish effects of selection from other genetic factors. The SacI-digested DNA was hybridized individually with MHC class II and MHC class IV gene probes. The MHC class II RFLP analysis revealed four polymorphic bands and only one of them showed a significant difference between the selection directions H and L pooled between replicates. The small frequency differences of this band relative to the long-term selection suggest that this MHC class II fragment may contain genetic elements that are only slightly associated with the immune response traits used for selection. The hybridization with the MHC class IV probe displayed 26 scorable bands, of which 18 were polymorphic. In most instances, the differences between the lines were likely caused by the influence of genetic factors other than selection for multitrait immunocompetence. Only one band displayed a consistency in difference between selection directions in both replicates and no frequency difference between replicates. This band was almost completely absent in both H sublines, but at a frequency of about 50% in both L sublines. The general results of this study did not reveal major differences in band frequencies that indicate a close association of MHC class II and MHC class IV polymorphic markers to the divergent selection for multitrait immune response. Although the MHC makes a crucial contribution in immune response, it may have been difficult to detect single-gene associations with the selection criteria of this study, because of the myriad of components contributing to general immune responses measured in vivo.

Major histocompatibility complex (MHC) related cDNA probes associated with antibody response in meat-type chickens

The major histocompatibility complex (MHC) region was examined as a set of candidate genes for association between DNA markers and antibody response. Intercross F2 families of chickens were generated from a cross between high (HC) and low (LC) Escherichia coli(i) antibody lines. Restriction fragment length polymorphism (RFLP) analysis was conducted by using three MHC-related cDNA probes: chicken MHC class IV (B-G), chicken MHC class I (B-F), and human MHC-linked Tap2. Association between RFLP bands and three antibody response traits (E. coli, sheep red blood cells and Newcastle disease virus) were determined by two methods: by statistically analyzing each band separately and also by analyzing all bands obtained from the three probes by using multiple regression analysis to account for the multiple comparisons. The MHC class IV probe was the highest in polymorphisms but had the lowest number of bands associated with antibody response. The MHC class I probe yielded 15 polymorphic bands of which four exhibited association with antibody response traits. The Tap2 probe yielded 20 different RFLP bands of which five were associated with antibody production. Some Tap2 bands were associated with multiple antibody response traits. The multiband analysis of the three probes' bands revealed more significant effects than the analysis of each band separately. This study illustrates the efficacy of using multiple MHC region probes as candidate markers for quantitative trait loci (QTLs) controlling antibody response in chickens.

Impact of genetics on disease resistance

The genetics of a bird or flock has a profound impact on its ability to resist disease, because genetics define the maximum achievable performance level. Careful attention should be paid to genetics as an important component of a comprehensive disease management program including high-level biosecurity, sanitation, and appropriate vaccination programs. Some specific genes (e.g., the MHC) are known to play a role in disease resistance, but resistance is generally a polygenic phenomenon. Future research directions will expand knowledge of the impact of genetics on disease resistance by identifying non-MHC genetic control of resistance and by further elucidating mechanisms regulating expression of genes related to immune response.

Differential antibody responses in 6.B major histocompatibility (B) complex congenic chickens

Lines 6.6-2 (B2B2) and 6.15-5 (B2B2), congenic for the major histocompatibility (B) complex with > 99.9% background gene uniformity, were used to examine primary antibody responses to two antigens. In each of two trials, 1 mL of 5% SRBC, a T cell-dependent antigen, or 0.1 mL of Brucella abortus (BA), a T cell-independent antigen, was injected into separate groups of each B genotype aged 3 and 6 wk. Blood samples were taken from the chickens 7 d after immunization. Serum titers (log2) for both total antibody and mercaptoethanol (ME)-sensitive antibody to detect IgG were assayed by microtiter procedures. Least squares analysis of variance and Fisher's protected Least Significant Difference at P < 0.05 were used to evaluate the data. The total anti-SRBC antibody titer was significantly higher in B5B5 chicks than in B2B2 chicks at 4 and 7 wk of age. There was no significant difference in ME sensitive antibody to SRBC. Chicks of the B5B5 genotype also had significantly higher total and IgG antibody titers to BA at both ages than B2B2 chicks. The results indicate that 4- and 7-wk-old B5B5 chicks had a significantly stronger antibody response to SRBC or BA than B2B2 chicks.

Immunogenetics and the major histocompatibility complex

The poultry immune system is a complex system involving many different cell types and soluble factors that must act in concert to give rise to an effective response to pathogenic challenge. The complexity of the immune system allows the opportunity for genetic regulation at many different levels. Cellular communication in the immune response, the production of soluble factors, and the rate of development of immune competency are all subject to genetic influences. The genes of the major histocompatibility complex (MHC) encode proteins which have a crucial role in the functioning of the immune system. The MHC antigens of chickens are cell surface glycoproteins of three different classes: Class I (B-F), Class II (B-L) and Class IV (B-G). The MHC antigens serve as essential elements in the regulation of cell-cell interactions. The MHC has been shown to influence immune response and resistance to autoimmune, viral, bacterial and parasitic disease in chickens. The MHC has been the primary set of genes identified with genetic control of immune response and disease resistance, but there are many lesser-characterized genes outside of the MHC that also regulate immunoresponsiveness. Polygenic control has been identified in selection experiments that have produced lines of chickens differing in antibody levels or kinetics of antibody production. These lines also differ in immunoresponsiveness and resistance to a variety of diseases. Understanding the genetic bases for differences in immunoresponsiveness allows the opportunity selectively to breed birds which are more resistant to disease. Indirect markers that can be used for this selection can include the MHC genes and immune response traits that have been associated with specific or general resistance to disease.

B-congenic chickens differ in macrophage inflammatory responses

The influence of the chicken major histocompatibility (B) complex (MHC) on monocyte and macrophage recruitment and activation was examined using fully developed 15I5-B congenic White Leghorn lines (ten backcross generations). The phagocytic activity of Sephadex-elicited peritoneal macrophages for sheep red blood cells (SRBCs) was highest in lines 15.7-B2 and 15.P-B13 and lowest in 15.15I-B5 and 15.N-B21. The same pattern of phagocytic activity was obtained when LPS (E. coli) was used as the in vivo elicitor-activator of peritoneal macrophages. Lines with B2 and B13 haplotypes had elevated percentages of phagocytic macrophages and a higher internalization activity per cell than did B5 and B21 congenic chickens. Differential peritoneal macrophage function between congenic lines was further supported by quantitation of superoxide anion release. B2 and B13 haplotypes were associated with high activity in contrast with B5, which was low, and 15I5 (B15) and B21 which were intermediate for superoxide anion release by macrophages. In vitro activation of blood monocytes with LPS resulted in similar line differences for SRBC phagocytic activity as were observed with in vivo Sephadex and LPS activation. In contrast, chemotaxis of blood mononuclear leukocytes to f-met-leu-phe produced a reciprocal response pattern among the haplotypes. Cells from lines with haplotypes B5 and B21 were superior to those of B2, B13, and B15 congenic lines in their directed migration towards this chemoattractant. All functional differences occurred despite similarities among lines in the cellular profiles of both elicited peritoneal exudate cells and isolated blood mononuclear cells.

The chicken major histocompatibility complex in disease resistance and poultry breeding

Numerous studies confirm that genes in the chicken major histocompatibility complex exert major genetic control over host resistance to autoimmune, viral, bacterial, and parasitic diseases. Examples of major histocompatibility complex associations with traits of growth and reproduction in the chicken are also available. Thus, the major effects of the major histocompatibility complex on the economically important traits of disease resistance, growth, and reproduction make the major histocompatibility complex a valuable subject for intensive analysis in agricultural species. This paper examines, as a model for integration of genetics and immunology, the research on the chicken major histocompatibility complex, which confirmed its role in genetic control of disease resistance, focusing on Marek's disease, a virally induced cancer. Current knowledge of associations of the chicken major histocompatibility complex with specific disease resistance, immune response, and other economic traits are selectively reviewed. Use of major histocompatibility complex typing in the poultry industry, including speculation about future applications, is presented.

Genetic control of immunity to Eimeria tenella. Interaction of MHC genes and non-MHC linked genes influences levels of disease susceptibility in chickens

The relative importance of MHC genes and background genes in the genetic control of disease susceptibility and the development of protective immunity to E. tenella infection was investigated in eight different strains of 15I5-B congenic and four inbred chicken strains. RPRL 15I5-B congenic chickens that share a common genetic background but express different B haplotypes demonstrated wide variations in disease susceptibility and the development of acquired resistance to E. tenella infection. Infection of chickens sharing a common B haplotype but expressing different genetic backgrounds showed quite contrasting levels of susceptibility to secondary E. tenella infection. In all chicken strains examined, infected chickens developed high levels of serum and biliary anti-coccidial antibodies regardless of their B haplotypes. Furthermore, no correlation between antibody levels and the phenotypically expressed levels of disease resistance was demonstrated. These findings lend support to the view that interaction of MHC genes and non-MHC genes influences the outcome of host response to E. tenella infection.

Eimeria acervulina: evaluation of the cellular and antibody responses to the recombinant coccidial antigens in B-congenic chickens

The roles of major histocompatibility complex (MHC) and non-MHC-linked genes in the genetic control of disease susceptibility and the development of protective immunity to Eimeria acervulina infection were investigated in six 15I5-B congenic and four different strains of chickens characterized for the MHC. When oocyst production was assessed, wide variations were noted following initial and challenge infections among the strains of chickens tested. In general, 15.N-21, 15.P-13, B21, B19, SC, and FP chickens were protected following challenge infection whereas 15I5, 15.P-19, 15.7-2, and 15.6-2 chickens were not. Strains of chickens sharing a same B haplotype on different genetic backgrounds did not show comparable levels of protection. These results lead to the view that non-MHC-linked genes have a profound influence on the outcome of the host response to E. acervulina infection. Chickens infected twice at 1-month intervals by an oral inoculation with E. acervulina developed both coccidial-specific antibody and T-cell responses. E. acervulina infected chickens showed T-cell-mediated immune responses to the intact sporozoites as well as to recombinant proteins, p130 of sporozoites and p150 of merozoites. Both p130 and p150 antigens have been identified and characterized previously. Sera obtained from all infected chickens recognized the p150 merozoite protein, but not the p130 sporozoite protein in immunoblots. In general, the cellular response, but not the antibody response to the p150 recombinant surface merozoite antigen correlated with the degree of protection following the challenge infection. These results suggest that the strains of chickens having improved protection against challenge infection demonstrate higher T-cell responses to the recombinant surface merozoite protein, p150.

Hypothesis: immunogenetic analysis of spontaneous autoimmune thyroiditis in obese strain (OS) chickens: a two-gene family model

Analysis of the number of genes involved in the regulation of the expression of SAT in OS, by means of crosses with the unrelated inbred CB line, gave the following results: 1) The production of Tg-AAb is regulated by one or two genes; 2) the sensitivity of the thyroid to autoimmune attack is under the control of about 3 genes; 3) the expression of SAT, as measured by mononuclear cell infiltration of the thyroid gland, is thus encoded by at least 4-5 genes (approximately 2 of which regulate the immune system hyperreactivity against antigens of the thyroid, and 3 of which regulate the sensitivity of the target organ to an attack by the immune system. It should, however, not be forgotten that this calculation, which results in 5 genes as being crucial for the development of SAT, is only valid for the combination of the OS and the CB inbred line. A different number might have arisen with the use of a different inbred line for crossing experiments. 4) The genes involved in the genetic control of SAT can be divided into two categories, major and minor genes. One family of major genes regulates the hyperreactivity of the immune system and perhaps its specificity for thyroid antigens. A second family of major genes encodes the target organ susceptibility to the attack of the immune system. The minor genes modulate the expression of the major genes and are especially important in animals with an incomplete set of major genes. The influence of sex hormones and the MHC are examples of such genes. MHC genes play an important role in outbred populations, but they are not a prerequisite for the development of the disease. Fully developed, early onset SAT is only seen in an animal where all major genes are present. The existence of two-gene families, each composed of relatively few genes, might guarantee to a species that SAT will not be too frequent in outbred populations.

MHC-chromosome dosage effects: evidence for increased expression of Ia glycoprotein and alteration of B cell subpopulations in neonatal aneuploid chickens

Quantitative variation in the expression of MHC-encoded class II (Ia) glycoproteins has been associated with stages of lymphocyte development and a number of disease conditions. We have used an avian MHC dosage model to study the regulation of Ia expression and the effects of quantitative variation in membrane Ia on B-cell development. Lymphocyte membrane expression of Ia glycoprotein molecules and the frequency of small-versus-large lymphocytes were examined in trisomic line chickens containing either two (disomic), three (trisomic), or four (tetrasomic) copies of the microchromosome encoding the MHC. This was accomplished by quantitative laser flow cytometry analysis of bursa-resident B lymphocytes from neonatal trisomic line chickens. The aneuploids (trisomics and tetrasomics) expressed more cell surface Ia than did normal disomic birds. Furthermore, the aneuploids exhibited a greater frequency of small B lymphocytes as compared to disomic chickens. Dual parameter analysis of Ia quantity and cell size was undertaken to study B lymphocyte subpopulations in these birds. It was observed that the aneuploids had altered frequencies of two distinct subpopulations of cells: (1) an increased percentage of small cells which express high levels of Ia antigen and (2) a decreased percentage of large cells which express medium levels of Ia antigen. These findings support the view that MHC class II genes are regulated and expressed in a dosage-dependent manner. Therefore, increases in the number of MHC copies per cell result in the increased expression of Ia glycoprotein on bursa-resident B cells. The stepwise increase in membrane Ia on trisomic and tetrasomic B cells is correlated, and perhaps casually linked, with progressive degrees of alteration of developing B cell subpopulations in the bursa of aneuploid chicks. These events may ultimately alter the humoral immunity of the aneuploid animals.

Genetic resistance to fowl cholera is linked to the major histocompatibility complex

Chickens of the Iowa State S1 line have been selected for ability to regress Rous sarcoma virus-induced (RSV) tumors, humoral immune response to GAT (Ir-GAT), and erythrocyte antigen B. Sublines homozygous at the major histocompatibility complex (MHC), as well as F1 heterozygotes and F2 segregants, were tested for resistance to fowl cholera by challenge with Pasteurella multocida strain X73. Control of the response at high doses was associated in a preliminary study with Ir-GAT and response to RSV tumors. Genetic control of resistance to low doses of P. multocida was demonstrated via sublines and F2 segregants to be linked with genes of the B-G region. Thus, genetic control of resistance to fowl cholera in chickens after exposure to Pasteurella multocida was shown to be linked to the major histocompatibility B complex, in this first demonstration of MHC-linked resistance to bacterial disease challenge.

Subregions and functions of the chicken major histocompatibility complex

The chicken major histocompatibility complex (MHC) exerts genetic influence over a variety of important biological functions including immune response, disease resistance, growth and development, aging, and reproduction. The chicken MHC possesses at least three subregions encoding distinct gene products. The B-G subregion encodes antigens unique to erythrocyte surfaces. The B-L and B-F subregions encode cell surface glycoproteins homologous to mammalian Class II and Class I antigens, respectively. Class I and Class II molecules are crucial for recognition of self vs. nonself and for cell communication, and therefore are fundamental for all immune responses. Studies of chromosomal recombinants have been particularly useful in eliciting the structure and function of subregions of the chicken MHC.

Tests of association of immunoglobulin allotype genes and viral oncogenesis in chickens

Chickens from Regional Poultry Research Laboratory (RPRL) inbred line 6(3) are resistant to virally-induced Marek's disease (MD) and lymphoid leukosis (LL) and are relatively strong regressors of virally-induced Rous sarcomas. In contrast, RPRL line 100 chickens are highly susceptible to MD and LL and are weaker regressors of Rous sarcomas than line 6(3). RPRL lines 100 and 6(3) differ for alleles at the IgG-1 (G-1) allotype locus, but have identical IgM-1 (M-1) allotype alleles. To test the possible association of the G-1 locus with variations in resistance to virally-induced tumors, homozygous and heterozygous genotypes among F3 crosses were infected. F3 chickens with different G-1 types were comparable in their resistance to MD tumors following inoculation with the JM strain of the MD virus, and for their ability to regress Rous sarcoma tumors induced by the Rous sarcoma virus (RSV) RAV-1. However, following RAV-1 virus infection a smaller proportion of G-1a/G-1aF3 or F4 birds developed LL tumors than G-1a/G-1e and G-1e/G-1e birds. Genes determining immunoglobulin heavy chains were therefore associated with a recessive resistance to B-cell lymphomagenesis in chickens.

Equine leucocyte antigen system: progress and potential

Leucocyte antigens are cell-surface glycoproteins, the structure of which is under the genetic control of a chromosome region called the major histocompatibility complex. Progress in the study of the equine leucocyte antigen (ELA) system has been achieved in two ways; first by the fact that the ELA system is intensively investigated in different laboratories all over the world and parallels can be drawn to the information gained from research in more extensively studied species, and secondly by the collaborative efforts of the participants in three international workshops. The potential applications of the ELA system and areas of further investigation are discussed.

MHC- and non-MHC-encoded surface antigens of chicken lymphoid cells and erythrocytes recognized by polyclonal xeno-, allo- and monoclonal antibodies

Surface antigens on chicken thymus and bursa cells were analyzed by immunoprecipitation using polyclonal and monoclonal antisera raised against (and specific for) thymus (ATS) or bursa (ABS) cells, respectively. The antigens identified were compared with those governed by the B-F, B-L and B-G regions of the chicken major histocompatibility complex (B complex). Four proteins were precipitated from thymus cells by 2 polyclonal ATS: both antisera recognized molecules of apparent molecular mass of 172-182, 132-135, 75-76 kDa, and one antiserum in addition recognized a protein of 102 kDa. The 172-182 and 102-kDa peaks were still demonstrable under reducing conditions indicating that they are composed of a single polypeptide chain, the other 2 were lost under reducing conditions, therefore, must be composed of smaller subunits. Of the 2 monoclonal ATS tested, one identified a single protein of 186 kDa and the other a 135-kDa protein (in addition to 2 smaller molecules); whether these are the same as those precipitated by the polyclonal antisera remains to be determined as they behaved differently under reducing conditions. Proteins of 162 and 78-84 kDa were revealed by 2 polyclonal ABS under nonreducing conditions but the former may in one case be a polymer (it disappeared under reducing conditions) and in the other a single molecule. In addition molecules of 182 kDa were identified by one antiserum and of 84 and 60 kDa by the other under nonreducing conditions. Of the 4 monoclonal ABS only one identified a 200-kDa protein: molecules of 115-125, 90-100, 48-52 and 40-43 kDa were also precipitated, all of which were reduced to smaller molecules. With 2 specific anti-B-F alloantisera we were able to precipitate the "conventional" B-F antigen from red blood cell lysates of CB-strain chickens resolving into a 40-kDa peak and a light chain of about 12 kDa corresponding to beta 2 microglobulin. Precipitates from peripheral blood lymphocytes, bursa and thymus cells revealed an additional protein of 22 kDa. With 2 specific B-L alloantisera two peaks of 33 kDa and 31 kDa were obtained from peripheral blood lymphocytes. Using anti-B-G alloantisera a double band corresponding to 47 and 42 kDa was seen under reducing conditions. There is no evidence from these data to indicate that the polyclonal and monoclonal antibodies are directed towards major histocompatibility complex antigens.

Allelic frequencies in eight alloantigen systems of chickens selected for high and low antibody response to sheep red blood cells

Parents and offspring from lines of chickens selected for high (HA) and low (LA) antibody response to sheep red blood cell antigen(s) were blood typed for systems A, B, C, D, E, H, I, and L. All birds were homozygous for allele L2, and allelic frequencies for the I system were essentially identical in both lines. In contrast, allelic frequencies of the other blood group systems differed rather markedly between the HA and LA lines.

Natural haemagglutinins and immune responsiveness in young chicks

Titres of natural haemagglutinins to sheep erythrocytes and of experimentally induced antibodies to Newcastle disease virus (NDV), bovine serum albumin (BSA) and human gammaglobulin (HgG) were determined in White Rock broiler chicks immunised at 28 days of age. There was no relationship between levels of natural haemagglutinins and induced antibody levels or between titres of antibody to NDV and titres of antibody to BSA or HgG. A highly significant correlation (r=0.37) was found between titres of antibody to BSA and to HgG.

Genetic control of serum immunoglobulin G levels in the chicken

Serum IgG (7S) levels differed significantly for chickens from 10 different inbred lines. Within lines differences between B blood groups were statistically significant. The genetic control of serum IgG was further examined using birds from B complex haplotypes marked at the B locus and the Ir-GAT locus. Birds from each of five subgroup haplotypes (B1B1 Ir-GAT-Lo and -Hi, B19B19 Ir-GAT-Lo and -Hi, and B2B2 Ir-GAT intermediate) were tested for levels of serum IgG at 3, 6, 9, and 21 weeks of age. The rate and level of IgG reached in the serum was more than two-fold greater in the GAT-Hi birds than in the GAT-Lo. The Ir region of the B complex exerts some control over the ontogenesis of IgG, though most of the genetic variation seems not to be B complex associated.

Chicken major histocompatibility complex and disease

The chicken MHC (B complex) initially described by Briles as controlling blood antigens, is now known to be composed of at least three regions, L, F and G. Two of these, F and G, were described on the basis of recombinants found in a study of over 10,000 chickens. On the basis of biochemical, tissue distribution and functional analyses, F corresponds to the murine H-2 K/D regions. The G region is unique to the chicken since the antigenic product is expressed only on erythrocytes and their progenitors. L was identified by serological studies and corresponds to the H-2 I region; the L antigen is expressed predominantly on B lymphocytes, monocytes and 10% of T lymphocytes, and differences in the L region result in variations in immune responsiveness. A number of functional similarities exist between the chicken MHC and that of other species such as regulation of graft rejection, graft-versus-host reaction (GVHR) and mixed lymphocyte reactions (MLR), mitogenic and immune responsiveness and resistance to RNA and DNA virus infection. The chicken MHC also controls the severity of autoimmune disease, as exemplified by the spontaneous thyroiditis of Obese strain (OS) chickens. It differs from mammalian MHC's by having of lower crossing-over frequency and no apparent gene duplication.

B-L antigens (Ia-like antigens) of the chicken major histocompatibility complex

This paper reviews the present knowledge of B-L antigens encoded by the chicken B complex as regards to the following aspects: (1) identification and cellular expression, (2) structural studies, (3) evidence for two distinct populations of B-L antigens, (4) mapping of B-L loci of the B complex, (5) B-L and immune response, and (6) the role of the B-L antigens for the control of mixed lymphocyte reactions (MLR) and graft-versus-host (GVH) reactions. It is concluded that B-L antigens of the chicken exhibit extensive homology with mammalian Ia antigens. A genetic map of the B complex is presented.

Role of the B-G-region antigen in the humoral immune response to the B-F-region antigen of chicken MHC

In the chicken MHC there exist two regions, designated F and G, which were separated by crossing-over. The F region contains genes controlling all functions characteristic of the MHC. So far only one gene has been assigned to the G region and it is responsible for the presence of an RBC antigen. When cross-immunizing animals of the congenic lines CB and CC with erythrocytes, we have found that both F- and G-specific antibodies were produced. By using the recombinant haplotypes Br1 and Br2 we were able to dissociate the F from the G antigen and immunize with them separately. It was found that production of F antibodies required the copresence of the G antigen, whereas G antibodies were formed regardless of the presence of absence of the F-region antigen. It could be demonstrated that a prerequisite of the role of the G antigen with respect to the F antigen was the localization of both antigens on the same erythrocyte. Possible mechanisms underlying this phenomenon are discussed.

Genetic control of T-lymphocyte mitogenesis in chickens

The in vitro mitogenic response to PHA and Con A was determined in three inbred lines of chickens. Lymphocytes from one line consistently showed a greater stimulation by PHA than the other two lines. Analysis of F1 crosses and backcrosses indicated that this quantitative difference was controlled by more than one gene. More substantial differences in Con-A stimulation were also observed between the three lines, and the data indicated that separate genetic systems were controlling the variation in PHA and Con-A stimulation. Analysis of F1 crosses, backcrosses and assortative matings between backcrosses revealed that the variation in Con-A stimulation was controlled by at least two major genes, one of which may be linked to the major histocompatibility complex. Surprisingly, one line appeared to be segregating for Con-A stimulation in spite of an inbreeding coefficient greater than 0.98.

Evidence for two populations of B-L (Ia-like) molecules encoded by the chicken MHC

Two specific alloantisera detecting B-L (Ia-like) antigens on chicken lymphocytes of the B6 and B15 haplotypes were found to cross-react strongly. Anti-B-L6 and anti-B-L15 alloantisera both reacted with B-L molecules on B6 and B15 lymphocytes as demonstrated by immunofluorescence and SDS-PAGE analysis of 125I-labeled B-L antigens isolated by incubation with anti-B-L alloantisera. Absorption studies showed that the anti-B-L alloantisera reacted with at least two kinds of antigenic determinant, one set shared by B-L6 and B-L15 molecules and another set specific for each haplotype. In spite of the absence of genetic evidence for more than one B-L locus in the chicken B complex, it was shown by sequential antibody incubations that these two different B-L antigenic determinants are associated with at least two separate species of B-L molecules, indicating the presence of at least two B-L loci within the MHC of the chicken.

Rous sarcoma regression in seven highly inbred lines of White Leghorns

Response to Rous sarcoma virus (RSV)-induced tumors was studied in Regional Poultry Research Laboratory (RPRL) lines 61, 63, 72, 100, 151, and 15I5 and in Reaseheath line C, all highly inbred White Leghorn stocks. Virus inoculations were made in chickens at 6 weeks of age. Tumors were scored subjectively for size on a regular basis and in some instances a tumor profile index (TPI) was assigned which characterized tumor development over a 10 week period for each chicken (TPI 1 = complete regression in 28 days; TPI 5 = terminal tumor). The frequency of tumor regression, terminal tumors, and metastases and mean TPI was examined. The incidence of tumor regression ranged from 92% in line 61 to 0 % in lines 151 and 15I5. The frequency of terminal tumors varied from 100% in line 151 to 2% in line61, while metastasis in chickens with terminal tumors differed from 92% in line 15I5 to 0% in line 61. Mean TPI ranged from 2.0 in line 61 to 4.6 in line 15I5 and 4.7 in line C. The erythrocyte alloantigen genotype at the B blood group locus, (part of the B complex, MHC) and 11 additional blood group loci were known for each of the lines. The data indicate that genetic differences in tumor regression may be pronounced between inbred lines which share similar, if not identical, B locus erythrocyte alloantigens and that other unknown genes are also involved.

Genetics of Ia-like alloantigens in chickens and linkage with B major histocompatibility complex

Two sets of backcross matings were performed to test for linkage between genes coding for the Ia-like antigens ("Ia") and the B erythrocyte antigens (Ea-B) of the chicken. Evidence is presented which indicates that the "Ia" antigens are determined by a single codominant locus and that the Ea-B and "Ia" loci are on the same chromosome. Failure to detect a single recombinant between the Ea-B and "Ia" loci out of 208 progeny suggests close linkage of the two genes with a map distance of up to about 2 centimorgans. The "Ia" genes are thus included in the B major histocompatibility complex of the chicken.

B-complex genetic control of immune response to HSA, (T,G)-A--L, GT and other substances in chickens

Immune response to poly-(L-tyrosine-L-glutamic acid)-poly-D,L-alanine-poly-L-lysine (T,G)-A--L), human serum albumin (HSA), and (L-glutamic acid50, L-tyrosine50)n (GT) was found to be linked to the B complex in an outbred line of Leghorns segregating for the B1, B2, and B19 alleles. Birds of the blood group genotypes B1B1, B2B2, and B19B19 were low, intermediate, and high responders, respectively to either (T,G)-A--L or HSA. Response to GT, however, differed, with the B2B2 genotype being the only responder. No real genotype differences in immune response to DNP-congugates and sheep red blood cells (SRBC) could be detected.

Role of B cells in the expression of genetic resistance to growth of Rous sarcoma in the chicken

Resistance to the development of progressively growing tumors induced by Rous sarcoma virus is a dominant trait controlled by a gene linked to the major histocompatibility complex (MHC). The effect of bursectomy (Bx) on the expression of this trait was studied in two inbred lines of chickens homozygous for different MHC alleles, and which differ with respect to the gene controlling resistance to Rous tumors. The results show that Bx alters the expression of the trait, since genetically resistant birds were rendered highly susceptible to progressive tumor growth. The bursa of Fabricius thus makes an important contribution to resistance. The results do not indicate whether genetic resistance is mediated exclusively by B cells or by another bursa-dependent population.

Marek's disease: effects of B histocompatibility alloalleles in resistant and susceptible chicken lines

Lines of chickens selected from a common ancestral population for either resistance or susceptibility to Marek's disease developed contrasting frequencies of particular B alloalleles. Comparison of inoculated sibs in backcross-families revealed that the B alloalleles characterizing the two lines accounted for an eightfold difference in tumor incidence. This genetic difference in tumorigenesis associated with the alloalleles of the major histocompatibility complex is probably expressed through the cell-mediated immune system.