Antigens similar to major histocompatibility complex B-G are expressed in the intestinal epithelium in the chicken

Innate immune genes of the chicken MHC and related regions

Compared to the major histocompatibility complex (MHC) of typical mammals, the chicken BF/BL region is small and simple, with most of the genes playing central roles in the adaptive immune response. However, some genes of the chicken MHC are almost certainly involved in innate immunity, such as the complement component C4 and the lectin-like receptor/ligand gene pair BNK and Blec. The poorly expressed classical class I molecule BF1 is known to be recognised by natural killer (NK) cells and, analogous to mammalian immune responses, the classical class I molecules BF1 and BF2, the CD1 homologs and the butyrophilin homologs called BG may be recognised by adaptive immune lymphocytes with semi-invariant receptors in a so-called adaptate manner. Moreover, the TRIM and BG regions next to the chicken MHC, along with the genetically unlinked Y and olfactory/scavenger receptor regions on the same chromosome, have multigene families almost certainly involved in innate and adaptate responses. On this chicken microchromosome, the simplicity of the adaptive immune gene systems contrasts with the complexity of the gene systems potentially involved in innate immunity.

Functional Alleles of Chicken BG Genes, Members of the Butyrophilin Gene Family, in Peripheral T Cells

γδ T cells recognize a wide variety of ligands in mammals, among them members of the butyrophilin (BTN) family. Nothing is known about γδ T cell ligands in chickens, despite there being many such cells in blood and lymphoid tissues, as well as in mucosal surfaces. The major histocompatibility complex (MHC) of chickens was discovered because of polymorphic BG genes, part of the BTN family. All but two BG genes are located in the BG region, oriented head-to-tail so that unequal crossing-over has led to copy number variation (CNV) as well as hybrid (chimeric) genes, making it difficult to identify true alleles. One approach is to examine BG genes expressed in particular cell types, which likely have the same functions in different BG haplotypes and thus can be considered “functional alleles.” We cloned nearly full-length BG transcripts from peripheral T cells of four haplotypes (B2, B15, B19, and B21), and compared them to the BG genes of the B12 haplotype that previously were studied in detail. A dominant BG gene was found in each haplotype, but with significant levels of subdominant transcripts in three haplotypes (B2, B15, and B19). For three haplotypes (B15, B19, and B21), most sequences are closely-related to BG8, BG9, and BG12 from the B12 haplotype. We found that variation in the extracellular immunoglobulin-variable-like (Ig-V) domain is mostly localized to the membrane distal loops but without evidence for selection. However, variation in the cytoplasmic tail composed of many amino acid heptad repeats does appear to be selected (although not obviously localized), consistent with an intriguing clustering of charged and polar residues in an apparent α-helical coiled-coil. By contrast, the dominantly-expressed BG gene in the B2 haplotype is identical to BG13 from the B12 haplotype, and most of the subdominant sequences are from the BG5-BG7-BG11 clade. Moreover, alternative splicing leading to intron read-through results in dramatically truncated cytoplasmic tails, particularly for the dominantly-expressed BG gene of the B2 haplotype. The approach of examining “functional alleles” has yielded interesting data for closely-related genes, but also thrown up unexpected findings for at least one haplotype.

Brief review of the chicken Major Histocompatibility Complex: the genes, their distribution on chromosome 16, and their contributions to disease resistance

Nearly all genes presently mapped to chicken chromosome 16 (GGA 16) have either a demonstrated role in immune responses or are considered to serve in immunity by reason of sequence homology with immune system genes defined in other species. The genes are best described in regional units. Among these, the best known is the polymorphic major histocompatibility complex-B (MHC-B) region containing genes for classical peptide antigen presentation. Nearby MHC-B is a small region containing two CD1 genes, which encode molecules known to bind lipid antigens and which will likely be found in chickens to present lipids to specialized T cells, as occurs with CD1 molecules in other species. Another region is the MHC-Y region, separated from MHC-B by an intervening region of tandem repeats. Like MHC-B, MHC-Y is polymorphic. It contains specialized class I and class II genes and c-type lectin-like genes. Yet another region, separated from MHC-Y by the single nucleolar organizing region (NOR) in the chicken genome, contains olfactory receptor genes and scavenger receptor genes, which are also thought to contribute to immunity. The structure, distribution, linkages and patterns of polymorphism in these regions, suggest GGA 16 evolves as a microchromosome devoted to immune defense. Many GGA 16 genes are polymorphic and polygenic. At the moment most disease associations are at the haplotype level. Roles of individual MHC genes in disease resistance are documented in only a very few instances. Provided suitable experimental stocks persist, the availability of increasingly detailed maps of GGA 16 genes combined with new means for detecting genetic variability will lead to investigations defining the contributions of individual loci and more applications for immunogenetics in breeding healthy poultry.

Aflatoxicosis chemoprevention by probiotic Lactobacillius and lack of effect on the major histocompatibility complex

Turkeys are extremely sensitive to aflatoxin B1 (AFB1) which causes decreased growth, immunosuppression and liver necrosis. The purpose of this study was to determine whether probiotic Lactobacillus, shown to be protective in animal and clinical studies, would likewise confer protection in turkeys, which were treated for 11 days with either AFB1 (AFB; 1 ppm in diet), probiotic (PB; 1 × 10(11) CFU/ml; oral, daily), probiotic + AFB1 (PBAFB), or PBS control (CNTL). The AFB1 induced drop in body and liver weights were restored to normal in CNTL and PBAFB groups. Hepatotoxicity markers were not significantly reduced by probiotic treatment. Major histocompatibility complex (MHC) genes BG1 and BG4, which are differentially expressed in liver and spleens, were not significantly affected by treatments. These data indicate modest protection, but the relatively high dietary AFB1 treatment, and the extreme sensitivity of this species may reveal limits of probiotic-based protection strategies.

Sequence of a complete chicken BG haplotype shows dynamic expansion and contraction of two gene lineages with particular expression patterns

Many genes important in immunity are found as multigene families. The butyrophilin genes are members of the B7 family, playing diverse roles in co-regulation and perhaps in antigen presentation. In humans, a fixed number of butyrophilin genes are found in and around the major histocompatibility complex (MHC), and show striking association with particular autoimmune diseases. In chickens, BG genes encode homologues with somewhat different domain organisation. Only a few BG genes have been characterised, one involved in actin-myosin interaction in the intestinal brush border, and another implicated in resistance to viral diseases. We characterise all BG genes in B12 chickens, finding a multigene family organised as tandem repeats in the BG region outside the MHC, a single gene in the MHC (the BF-BL region), and another single gene on a different chromosome. There is a precise cell and tissue expression for each gene, but overall there are two kinds, those expressed by haemopoietic cells and those expressed in tissues (presumably non-haemopoietic cells), correlating with two different kinds of promoters and 5′ untranslated regions (5′UTR). However, the multigene family in the BG region contains many hybrid genes, suggesting recombination and/or deletion as major evolutionary forces. We identify BG genes in the chicken whole genome shotgun sequence, as well as by comparison to other haplotypes by fibre fluorescence in situ hybridisation, confirming dynamic expansion and contraction within the BG region. Thus, the BG genes in chickens are undergoing much more rapid evolution compared to their homologues in mammals, for reasons yet to be understood.

Many immune genes are multigene families, presumably in response to pathogen variation. Some multigene families undergo expansion and contraction, leading to copy number variation (CNV), presumably due to more intense selection. Recently, the butyrophilin family in humans and other mammals has come under scrutiny, due to genetic associations with autoimmune diseases as well as roles in immune co-regulation and antigen presentation. Butyrophilin genes exhibit allelic polymorphism, but gene number appears stable within a species. We found that the BG homologues in chickens are very different, with great changes between haplotypes. We characterised one haplotype in detail, showing that there are two single BG genes, one on chromosome 2 and the other in the major histocompatibility complex (BF-BL region) on chromosome 16, and a family of BG genes in a tandem array in the BG region nearby. These genes have specific expression in cells and tissues, but overall are expressed in either haemopoietic cells or tissues. The two singletons have relatively stable evolutionary histories, but the BG region undergoes dynamic expansion and contraction, with the production of hybrid genes. Thus, chicken BG genes appear to evolve much more quickly than their closest homologs in mammals, presumably due to increased pressure from pathogens.

Extended gene map reveals tripartite motif, C-type lectin, and Ig superfamily type genes within a subregion of the chicken MHC-B affecting infectious disease

MHC haplotypes have a remarkable influence on whether tumors form following infection of chickens with oncogenic Marek's disease herpesvirus. Although resistance to tumor formation has been mapped to a subregion of the chicken MHC-B region, the gene or genes responsible have not been identified. A full gene map of the subregion has been lacking. We have expanded the MHC-B region gene map beyond the 92-kb core previously reported for another haplotype revealing the presence of 46 genes within 242 kb in the Red Jungle Fowl haplotype. Even though MHC-B is structured differently, many of the newly revealed genes are related to loci typical of the MHC in other species. Other MHC-B loci are homologs of genes found within MHC paralogous regions (regions thought to be derived from ancient duplications of a primordial immune defense complex where genes have undergone differential silencing over evolutionary time) on other chromosomes. Still others are similar to genes that define the NK complex in mammals. Many of the newly mapped genes display allelic variability and fall within the MHC-B subregion previously shown to affect the formation of Marek's disease tumors and hence are candidates for genes conferring resistance.

Characterisation of a cluster of TRIM-B30.2 genes in the chicken MHC B locus

We have identified and characterised a cluster of six TRIM-B30.2 genes flanking the chicken BF/BL region of the B complex. The TRIM-B30.2 proteins are a subgroup of the TRIM protein family containing the tripartite motif (TRIM), consisting of a RING domain, a B-box and a coiled coil region, and a B30.2-like domain. In humans, a cluster of seven TRIM-B30.2 genes has been characterised within the MHC on Chromosome 6p21.33. Among the six chicken TRIM-B30.2 genes two are orthologous to those of the human MHC, and two (TRIM41 and TRIM7) are orthologous to human genes located on Chromosome 5. In humans, these last two genes are adjacent to GNB2L1, a guanine nucleotide-binding protein gene, the ortholog of the chicken c12.3 gene situated in the vicinity of the TRIM-B30.2 genes. This suggests that breakpoints specific to mammals have occurred and led to the remodelling of their MHC structure. In terms of structure, like their mammalian counterparts, each chicken gene consists of five coding exons; exon 1 encodes the RING domain and the B-box, exons 2, 3 and 4 form the coiled-coil region, and the last exon represents the B30.2-like domain. Phylogenetic analysis led us to assume that this extended BF/BL region may be similar to the human extended class I region, because it contains a cluster of BG genes sharing an Ig-V like domain with the BTN genes (Henry et al. 1997a) and six TRIM-B30.2 genes containing the B30.2-like domain, shared with the TRIM-B30.2 members and the BTN genes.

Identification of new major histocompatibility complex class II restriction fragment length polymorphisms in a closed experimental line of Beltsville Small White turkeys

Beltsville Small White (BSW) turkeys have been utilized as an experimental model in the study of bacterial, parasitic, and fungal diseases. Given the critical role of MHC antigens in the initial steps of the immune response to specific pathogens, the MHC Class II of BSW turkeys was characterized. Southern blot analysis of PvuII-digested turkey DNA that was hybridized with a chicken Class II beta gene genomic clone revealed two restriction fragment length polymorphism profiles not previously identified in experimental or commercial breeder lines of turkeys. These fingerprint profiles differed in a single 6.0-kb band that was present in approximately 38% of the birds examined. The DNA fragments of 5.0, 4.1, 3.3, and 3.1 were present in both profiles. Furthermore, no mixed lymphocyte reaction was observed between individuals within the BSW turkey line. The present results indicate that BSW turkeys represent a unique source of genetic diversity for MHC Class II haplotypes.

Ultrastructural characteristics and lectin-binding properties of M cells in the follicle-associated epithelium of chicken caecal tonsils

To clarify the nature of M cells, the detailed ultrastructural characteristics and lectin-binding properties of M cells were investigated in follicle-associated epithelium (FAE) of chicken caecal tonsils. M cells presented various outlines from columnar to dome shaped. Their polymorphism was dependent on the number of harboured intraepithelial migrating cells. The lighter and larger nuclei of M cells were situated at more apical levels in the epithelial lining compared with those of neighbouring microvillous epithelial cells. The microvilli, which were significantly shorter and thicker than those of adjacent microvillous epithelial cells, were sparsely distributed or completely absent on the apical surfaces of M cells. In general, the apical cytoplasm of M cells without microvilli protruded slightly into the intestinal lumen. Numerous small vesicles were often contained in the apical cytoplasm. The numerous small invaginations of the apical and lateral cell surfaces suggested active transportation of luminal substances. No canaliculi existed in the apical cytoplasm of M cells whereas they were often detected in the neighbouring microvillous epithelial cells. A noteworthy finding was the frequent detection of multivesicular bodies in the apical cytoplasm of M cells. These multivesicular bodies suggest some degradation of ingested luminal substances during transcytoplasmic transportation. WGA and 4 other lectins strongly reacted with all epithelial cells except for M cells, this negativity suggesting a means of detecting M cells in chicken caecal tonsils. Three lectins, DSL, ConA and Jacalin, reacted weakly with the glycocalyx on M cells. The positive reactivity might allow chicken M cells to be utilised for specific antigen delivery into the mucosal immune system in some parenteral vaccinations.

Molecular characterization of major and minor MHC class I and II genes in B21-like haplotypes in chickens

The major histocompatibility complex (MHC) sequences of three B21-like haplotypes deriving from very different origins including the Red Jungle Fowl Gallus Gallus gallus were compared with the MHC sequences of the standard B21 haplotype from Scandinavian White Leghorn Gallus domesticus. The present analysis reveals two cDNA sequences for B-F and two cDNA sequences for B-LB for every B21-like haplotype, including B21 itself. Contrary to expectation, no sequence polymorphism in the antigen-binding domains of the MHC genes, between the investigated haplotypes, was found. The relative level of MHC class I molecules on the surface of leukocytes measured by flow cytometry was also analysed and found to be low in Marek's Disease (MD)-resistant B haplotypes (B21 and B21-like) and high in MD-susceptible B haplotypes (B15 and B19). However, in heterozygous (resistant/susceptible) animals, the relative level was almost as high as in susceptible haplotypes.

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.

Zipper protein, a B-G protein with the ability to regulate actin/myosin 1 interactions in the intestinal brush border

We recently identified a 28-kDa protein in the intestinal brush border that resembled tropomyosin in terms of size, homology, and alpha helical content. This protein contained 27 heptad repeats, nearly all of which began with leucine, leading to its name zipper protein. Subsequent analysis, however, indicated that both a 49-kDa and a 28-kDa immunoreactive protein existed in intestinal brush-border extracts. Using 5'-rapid amplification of cDNA ends analysis, we extended the N-terminal sequence of zipper protein to the apparent translation start site. This additional sequence contained a putative transmembrane domain and two potential tryptic cleavage sites C-terminal to the transmembrane domain which would release a 28-kDa cytoplasmic protein if utilized. The additional sequence was highly homologous to members of the B-G protein family, a family with no known function. Immunoelectron microscopy showed that zipper protein was confined to the membrane of the microvillus where it was in close association with brush-border myosin 1 (BBM1). Recombinant zipper protein (28-kDa cytoplasmic portion) blocked the binding of actin to BBM1 and inhibited actin-stimulated BBM1 ATPase activity. In contrast, zipper protein had no effect on endogenous or K/EDTA-stimulated BBM1 ATPase activity. Furthermore, zipper protein displaced tropomyosin from binding to actin, suggesting that these homologous proteins bind to the same sites on the actin molecule. We conclude that zipper protein is a transmembrane protein of the B-G family localized to the intestinal epithelial cell microvillus. The extended cytoplasmic tail either in the intact molecule or after tryptic cleavage may participate in regulating the binding and, thus, activation of BBM1 by actin in a manner similar to tropomyosin.

The influence of major histocompatibility complex genotypes on resistance to Pasteurella multocida and Newcastle disease virus in turkeys

Sublines homozygous for each of four MHC haplotypes were developed from randombred control populations of turkeys and challenged with Pasteurella multocida (capsular serogroup a, somatic serotype 3, 4) at 6 wk of age or Newcastle disease virus (NDV; Texas GB strain) at 4 wk of age. In addition, individuals from a randombred control line (RBC2) and a subline (F) of RBC2 long-term selected for increased 16-wk BW were included in most of the challenge trials. The duration of the challenge trials was 2 wk for both organisms. Mortality following challenge with P. multocida or NDV was higher in the F line than in its randombred control. The MHC genotypes differed in mortality following exposure to both organisms but the rankings of the genotypes were not the same for P. multocida and NDV. The increased susceptibility of the F line to both organisms could not be explained by known changes in the frequency of the MHC haplotypes.

Response of three class-IV major histocompatibility complex haplotypes to Eimeria acervulina in meat-type chickens

1. The importance of MHC genes and background genes in controlling disease resistance, including resistance to avian coccidiosis, has not been clarified in meat-type chickens. 2. The role of class IV MHC genes in resistance to Eimeria acervulina was assessed in F2 progeny of a cross between 2 meat-type lines, selected divergently for immune response to Escherichia coli. 3. Disease susceptibility was assessed by lesion score, body weight, packed cell volume and carotene absorption. 4. Chickens with the "K" class IV MHC haplotype had lower lesion scores than chickens with "F" and "A" haplotypes. 5. Plasma carotene concentrations were higher in chickens with "K" haplotype and lower in chickens with "F" and "A" haplotypes whereas body weight and packed cell volume were less sensitive measures of Eimeria infection. 6. Eimeria acervulina resistance appears to be associated with MHC class IV genes; information about MHC haplotypes may be useful in selecting for increased resistance of meat-type chickens to coccidiosis.

Survey of major histocompatibility complex class II haplotypes in four turkey lines using restriction fragment length polymorphism analysis with nonradioactive DNA detection

Four turkey lines were typed for MHC Class II haplotypes with restriction fragment length polymorphism (RFLP) analysis using a nonradioactive probe made from a chicken genomic clone of MHC Class II genes. The RFLP analysis detected 18 new patterns in the populations. There were three new haplotypes that had a frequency of about 10% or more in a population, whereas the rest appeared only once. The haplotype frequencies were significantly different in the E line, selected only for increased egg production, and the F line, selected only for increased body weight, compared with their respective randombred control lines. The shift of haplotype frequencies in the two selected lines seemed to be in opposite directions. One, but not the same, haplotype predominated in the selected lines, with about 50% of total haplotypes. Fewer haplotypes were frequent in the selected lines, whereas the frequencies in the control lines were relatively widely distributed, with the most frequent haplotype being below 35%. The frequency of homozygotes of the Class II haplotypes was the highest in the F line.

B-complex recombinants and sarcoma regression: role of B-L/B-F region genes

The anti-sarcoma response of three B complex recombinant haplotypes BR1(F24-G23), BR2(F2-G23), and BR3(F2-G23) was investigated. In a preliminary experiment, one male heterozygous for the BR1 recombinant haplotype and another heterozygous for the BR2 recombinant haplotype were each mated to females, some of which carried the respective recombinant. The anti-sarcoma response of progeny carrying the BR1 recombinant differed significantly from that of progeny carrying the BR2 recombinant. Subsequently, each of the three recombinant haplotypes was placed on each of four B haplotype complex backgrounds, and compared to B-G and B-L/B-F region controls on the same background haplotype. For each recombinant, significant differences in tumor growth were found between the recombinant and B-L/B-F control chickens on either one, two, or three of the four genetic backgrounds tested. For each recombinant, no differences were found between chickens carrying the recombinant and B-G region controls, which is further evidence that the gene(s) controlling Rous sarcoma growth lies in or near the B-L/B-F chromosomal region. Moreover, although the BR2 and BR3 recombinants appear to be identical serologically, they differed significantly in tumor growth suggesting that the two haplotypes are genetically different.

A class I cDNA from SPAFAS line-11 chickens

A chicken MHC class I (B-F) cDNA from SPAFAS line 11 embryonic liver tissue was isolated and characterized by nucleotide sequencing. Comparing this sequence with previously described B-F cDNAs highlights clustered nucleotide substitutions in exon 3, encoding amino acids located on the alpha-helical region of the alpha 2 domain.

Designation by restriction fragment length polymorphism of major histocompatibility complex class IV haplotypes in meat-type chickens

Major histocompatibility complex (MHC) class IV haplotypes were identified in a population of meat-type chickens by restriction fragment length polymorphism (RFLP) analysis. Fourteen different haplotypes were designated on the basis of restriction patterns obtained from Southern blots of PvuII- or BglII-digested DNA, hybridized with the MHC class IV cDNA probe bg32.1. Digestion with each restriction enzyme yielded the same level of polymorphism among individuals. For each haplotype, 4-10 restriction fragments ranging from 0.8 to 8 kb were observed. Such a designation of meat-type chicken MHC class IV haplotypes enables a rapid recognition of previously defined haplotypes, is readily adjustable to additional, newly found restriction patterns and could prove useful in practical breeding programmes.

Major histocompatibility complex class IV restriction fragment length polymorphism markers in replicated meat-type chicken lines divergently selected for high or low early immune response

Information on MHC may improve the efficiency of selection for immunological traits via the application of marker assisted selection or by selecting directly for a specific restriction fragment length polymorphism (RFLP) band or MHC haplotype. An experimental procedure is presented here for identifying MHC genes that are related to early immune response. A Class IV cDNA clone was used to probe Southern blots of erythrocyte genomic DNA from chickens. Chickens were taken from the second (S2) and third (S3) generations of replicated lines divergently selected for high antibody response (HC1, HC2) or low antibody response (LC1, LC2) to Escherichia coli vaccination at 10 days of age. These selection criteria have been found to be associated with other immunological parameters. The hypothesis that these selected lines differ in their MHC loci was evaluated by comparing the frequencies of MHC RFLP markers (single RFLP bands) and haplotypes (patterns of RFLP bands). The significant differences between LC and HC in the frequency of many MHC RFLP bands and of five MHC haplotypes indicate that early antibody production is influenced by MHC genes. The reliability of the association between the selection and frequency differences was tested and proven in most cases by analysis of the replicated lines. These differences in RFLP markers represent a change in allelic frequencies in MHC genes, probably due to selection. The results imply a connection between the Class IV genes and early antibody production, and they show the potential of prospective breeding not only by immunological phenotype but also by genotype (i.e., using RFLP markers of the MHC).

Differential resistance to Staphylococcus aureus challenge in major histocompatibility (B) complex congenic lines

Ten inbred B-congenic Leghorn lines were challenged with two isolates of Staphylococcus aureus at 3 days and 6 wk of age. Significant differences in mortality were observed among such lines when challenged at 3 days with either S. aureus Isolate P4L (moderately pathogenic) or S. aureus Isolate 3727 (highly pathogenic). Line 331 (B2/B2 genotype) had lower mortality than either Line 004 (B17/B17, chi 2 = 4.13, P < .05) or Line 253 (B18/B18, chi 2 = 4.23, P < .05) challenged with Isolate P4L. The use of a susceptibility index allowed for the detection of additional differences among the various lines challenged by Isolate 3727. Line 336 (BQ/BQ) was more resistant than either Line 335 (B19/B19, P < .01) or Line 330 (B21/B21, P < .01). No significant differences were found among the lines challenged at 6 wk by either isolate. The results provide additional evidence for the importance of the B complex in genetically determined disease resistance, and further demonstrate the usefulness of congenic lines in such investigations.

Major Histocompatibility Complex Class I Restriction Fragment Length Polymorphism Analysis in Highly Inbred Chicken Lines and Lines Selected for Major Histocompatibility Complex and Immunoglobulin Production

Selected chicken populations were analyzed by restriction fragment length polymorphism (RFLP) with a chicken MHC Class I (B-F) cDNA probe. The 13 highly inbred chicken lines differed in genetic origin and in MHC (B) haplotype, as distinguished by using hemagglutination with antisera against B-G and B-F antigens. The S1 sublines differed for B haplotype and antibody response to a synthetic polypeptide, GAT. In the highly inbred lines, band-sharing between lines from different origins was less than that between lines from same origin, showing the influence of the genetic background on chicken MHC Class I gene RFLP. In the S1 line, use of three restriction endonucleases (BglII, PvuII, and TaqI) produced MHC Class I RFLP patterns that were associated with B haplotype, but not with immune response to GAT (IrGAT). A previous study in the authors' laboratory also demonstrated an association of MHC Class II beta RFLP patterns with B haplotype, but not IrGAT, in the same line, suggesting that IrGAT is not controlled by MHC Class I or Class II beta genes.

B-G: we know what it is, but what does it do?

B-G molecules are polymorphic cell surface proteins that are encoded by the chicken MHC. Here, Jim Kaufman and Jan Salomonsen briefly summarize developments in the molecular genetics, the structure and the tissue distribution of B-G molecules, and discuss possible functions of this intriguing multigene family.

Immunoglobulin variable-region-like domains of diverse sequence within the major histocompatibility complex of the chicken

The highly polymorphic B-G antigens are considered to be part of the major histocompatibility complex (MHC) of the chicken, the B system of histocompatibility, because they are encoded in a family of genes tightly linked with the genes encoding MHC class I and class II antigens. To better understand these unusual MHC antigens, full-length B-G cDNA clones were isolated from B21 embryonic erythroid cell cDNA library, restriction-mapped, and sequenced. Five transcript types were identified. Analysis of the deduced amino acid sequences suggests that the B-G polypeptides are composed of single extracellular domains that resemble immunoglobulin domains of the variable-region (V) type, single membrane-spanning domains typical of integral membrane proteins, and long cytoplasmic tails. Sequence diversity among the five transcript types was found in all domains, notably including the B-G immunoglobulin V-like domains. The cytoplasmic tails of the B-G antigens are made up entirely of units of seven amino acid residues (heptads) that are typical of an alpha-helical coiled-coil conformation. The heptads vary in number and sequence between the different transcripts. The presence within B-G polypeptides of polymorphic immunoglobulin V-like domains warrants further investigations to determine the degree and nature of variability within this domain in these unusual MHC antigens.

Chicken major histocompatibility complex-encoded B-G antigens are found on many cell types that are important for the immune system

B-G antigens are a polymorphic multigene family of cell surface molecules encoded by the chicken major histocompatibility complex (MHC). They have previously been described only on cells of the erythroid lineage. By using flow cytometry, section staining, and immunoprecipitation with monoclonal antibodies and rabbit antisera to B-G molecules and by using Northern blots with B-G cDNA clones, we demonstrate here that B-G molecules and RNA are present in many other cell types: thrombocytes, peripheral B and T lymphocytes, bursal B cells and thymocytes, and stromal cells in the bursa, thymus, and caecal tonsil of the intestine. The reactions also identify at least one polymorphic B-G determinant encoded by the B-F/B-L region of the chicken MHC. The serology and tissue distribution of B-G molecules are as complex as those of mammalian MHC class I and class II molecules. These facts, taken with certain functional data, lead us to suggest that B-G molecules have an important role in the selection of B cells in the chicken bursa.