Major histocompatibility genes in egg-laying hens

Association of restriction fragment length polymorphisms of swine leucocyte antigen class I genes with production traits of Duroc and Hampshire boars

Restriction fragment length polymorphism analyses of swine leucocyte antigen (SLA) class I genes were performed on 70 Duroc and 38 Hampshire boars from the 1986-87 national performance tests of each breed in the USA. Few boars were inbred. Southern blotting and hybridization procedures were performed on genomic DNA, isolated from white blood cells, using PvuII endonuclease and a swine major histocompatibility complex (MHC) class I probe. Durocs had an average of 11 restriction fragments, with the most common being in 63% of the boars and the least common appearing in only one boar. Hampshire boars had an average of 12 restriction fragments, with the most common appearing in 73% of the boars and the least common appearing in only one boar. Least squares procedures and stepwise regression methods were used to examine the association between DNA restriction fragments and the selection index (INDEX), average daily gain (ADG), average backfat thickness (BF), loin muscle area (LEA), and age at 104 kg (DAY104). In the Duroc breed one DNA restriction fragment was associated with decreased INDEX (P less than 0.05) and decreased ADG (P less than 0.05) whereas two other fragments were associated with increased BF (P less than 0.05). In the Hampshire breed two restriction fragments were associated with an increase in INDEX (P less than 0.05). Cluster analyses were used to group pigs of each breed on the basis of similar RFLP patterns. One cluster group in the Duroc breed was associated with lower average INDEX values (P less than 0.05), greater average DAY104 (P less than 0.05), and a larger mean LEA (P less than 0.05). In the Hampshire breed one cluster group was associated with lower INDEX (P less than 0.05). These results suggest there may be an association between swine MHC class I genes and performance traits in swine. The use of SLA class I restriction fragments, as genetic markers, may have potential in the future for improving pig performance.

Resistance to Marek's disease virus in White Leghorn chickens: effects of avian leukosis virus infection genotype, reciprocal mating, and major histocompatibility complex

Genetic improvement for resistance to Marek's Disease (MD) in chickens continues to be of interest to the poultry industry. The aims of this study were to identify effects of the MHC on the molecular level and of avian leukosis virus (ALV) resistance status on MD mortality in two noninbred White Leghorn chicken lines that differ in B blood group type. Previously, within each of the chicken lines, sublines had been selected for resistance or susceptibility to ALV infection with Subgroups A and B. In this study, F2 offspring, obtained by crossing the two ALV-resistant or the two ALV-susceptible sublines, were tested for MD mortality after contact exposure at 1 d of age. Reciprocal matings were made in the grandparental generation. The MD mortality percentages, in an observation period of 17 wk, of F2 offspring from two hatches were 82.63 and 92.35%, respectively. Survival analysis (Cox model) was applied to assess the risk of dying from MD. No differences in MD mortality risk profiles were found between ALV-resistant and ALV-susceptible F2 offspring. Within ALV-susceptible F2 offspring, however, a reciprocal mating effect was observed in both hatches. The MHC Class I, II, and IV restriction fragment length polymorphism (RFLP) analyses were carried out on birds of the first hatch. Although two of 11 MHC class IV RFLP bands displayed a significant effect, in general, a strong association of MHC and MD mortality was not detectable.

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.

Major histocompatibility complex class II DNA polymorphisms in chicken strains selected for Marek's disease resistance and egg production or for egg production alone

The objective of this study was to investigate frequencies of major histocompatibility complex (MHC) class II restriction fragments in two groups of White Leghorn strains. Each group consisted of an unselected control, a strain selected for egg production traits, and a strain selected for egg production traits and Marek's disease (MD) resistance. PvuII-digested genomic DNA was hybridized with a chicken genomic MHC class II probe. The MHC class II DNA fragment frequencies in the selected strains differed from those in the related unselected control and in the strain selected using the same criteria from a different base population. Based on the sizes of the breeding populations, particularly those in the control strain and in the strain selected for egg production, it was considered unlikely that the observed changes of the MHC class II fragment frequencies were due to random genetic drift. The data suggested that some MHC class II bands are associated with production traits or with MD resistance, and that these associations tend to be unique to each genetic background. Hence, MHC class II genes are likely candidates for the investigation of quantitative trait loci in egg production and disease resistance traits such as those for which the studied strains were selected.

Direct and correlated responses to long-term selection for increased body weight and egg production in turkeys

Lines of turkeys were selected long-term for increased egg production (E line; 34 generations) or increased 16-wk BW (F line; 28 generations). The E and F lines were started from randombred control populations (RBC1 and RBC2, respectively) that were also maintained to remove environmental variation among generations. Realized heritabilities (h2) +/- SE in the E line, based on regressions of response on cumulated actual selection differentials (selection differentials weighted for the number of offspring produced), for 180-d and 250-d egg production were 0.34 +/- 0.02 (17 generations) and 0.26 +/- 0.13 (8 generations), respectively. The realized h2 of 16-wk BW in the F line was 0.26 +/- 0.01. There was no consistent evidence of selection response reaching a plateau in either line. The genetic association of BW and egg production changed with selection in the E and F lines. The genetic correlation varied from near zero to strongly negative and fluctuated between these extremes in both lines even though they started from different base populations and selection criteria differed. Other correlated responses to selection for increased egg production were increased average clutch length (intensity of lay), and decreased broodiness (total days lost), egg weight, shell coloration, and rate of response to stimulatory lighting. Other correlated responses to selection for increased 16-wk BW in the F line included: increased egg weight (due to increased albumen), longer eating bouts, and decreased average clutch length, semen production, walking ability, and resistance to Pasteurella multocida and Newcastle disease virus. Selection within the E and F lines also changed the frequency of MHC haplotypes and the changes appeared to be in opposite directions in the two lines.

Associations between major histocompatibility complex genes and production traits in White Leghorns

The frequency of the MHC haplotype B15 had been found in a previous study to be more than two times higher in a White Leghorn line selected for high egg production compared with the unselected control strain. To further evaluate these findings, matings were performed between chickens with the same heterozygous B genotypes, being combinations of the most frequent haplotypes, i.e., B15, B19, and B21. In total, more than 1,300 observations from two generations were analyzed. In each generation, approximately one half of the chickens were derived from the line selected for total egg mass, the other half from the control strain. The MHC genotypes were determined serologically. Additive and dominance effects of B haplotypes on production traits were analyzed using an individual animal model. The estimation of genotypic values, together with the analysis of gene substitution effects, showed that the B15 haplotype was associated with early sexual maturity and low egg production during the late production period, i.e., between 43 and 63 wk of age, whereas B19 was associated with later onset of sexual maturity. The association of B15 with early sexual maturity would thus explain the high frequency of the B15 haplotype previously observed in a line selected for high early egg production. No dominance effect of the B system was observed for any of the traits, suggesting that the present results were due predominantly to additive gene effects.

A major histocompatibility complex-linked locus in the rat critically influences resistance to diethylnitrosamine carcinogenesis

Major histocompatibility complex (MHC)-linked deletions in the rat are associated with defects in growth and development and increased susceptibility to chemical carcinogens. The present study maps a locus critical for determining susceptibility to diethylnitrosamine (DEN) carcinogenesis by using two groups of MHC-recombinant rats congenic for the MHC and its linked region. Resistance to DEN segregates with a locus (rcc+) that maps between RT1.E and ft, and its homozygous loss markedly increases susceptibility to DEN. Non-MHC genes do not significantly influence the susceptibility of these strains to DEN. The existence of the rcc locus adds support to our hypothesis that some genes in the MHC-linked region play a major role in both normal and abnormal growth.

Polygenic influences on the length of oestrous cycles in inbred mice involve MHC alleles

Genetic influences on female reproductive cycles were analysed in histocompatibility-congenic strains of mice. Oestrous cycles of young, virgin mice of inbred-congenic strains, hybrid crosses (F1), and parental-hybrid backcrosses (F2) were monitored for 3 months. Oestrous cycles were categorized by length (inter-oestrous interval): 4, 5, 6, or 7-14 days. Mice with the following H-2 haplotypes had a greater proportion of 5-day oestrous cycles: H-2b, H-2r, H-2h2, H-2h4, and H-2i5. In contrast, the H-2k and H-2d haplotypes had mostly 4-day oestrous cycles. Influences of H-2 haplotype were seen on two genetic backgrounds, C57BL/10Sn and C3H. Non-H-2 alleles were also implied by different patterns of cycles between strains with the same H-2b haplotype: C57BL/10Sn with predominantly 5-day cycles vs. C57BL/6J with a mix of 4- and 5-day cycles. The genetic basis for strain differences was investigation in F1 hybrids and their backcrosses. F1 hybrids of an H-2b (C57BL/10Sn; 5-day cycles) and an H-2k (B10.BR; 4-day cycles) strain had mostly 5-day cycles, indicating dominance of an H-2b allele(s). However, F1 hybrids from the reciprocal B6 x B10 cross (both H-2b) also display a preponderance of 5-day cycles, indicating dominance of a non-H-2 autosomal allele from the C57BL/10Sn strain. Among F2 mice, a '4-day' phenotype segregated with homozygosity for the k haplotype (P < 0.05, chi 2). These findings demonstrate the influence of genetic differences at the major histocompatibility complex on oestrous cycles.

Production traits and alloantigen systems in lines of chickens selected for high or low antibody responses to sheep erythrocytes

The selection of chickens for high (HA) and for low (LA) antibody titers to sheep erythrocytes has produced differences in the selected trait and in the correlated responses in body weight, egg production, and erythrocyte antigens. The response to selection continued through 14 generations. There was considerable divergence between lines for erythrocyte alloantigen systems, including the major histocompatibility complex. Females from Line LA were heavier as juveniles and lighter as adults, matured at a younger age, and had higher egg production than those from Line HA. There were no differences between lines for the incidence of defective eggs laid-except for the percentage of eggs with double-yolks, which was greater for Line LA than HA. The phenotypic correlations of antibody response with growth and with reproductive traits were very low; the genetic correlations were moderate to high for most of these traits.

The swine steroid 21-hydroxylase gene (CYP21): cloning and mapping within the swine leucocyte antigen complex

A swine genomic cosmid library constructed from a genotypically SLA homozygous Large White individual was screened with a murine genomic 21-hydroxylase probe. A clone which contained a pig 21-hydroxylase gene was isolated and after subcloning, the 5' region of the gene was sequenced. The deduced amino acid sequence corresponded almost exactly to the NH2 terminal portion of the steroid 21-hydroxylase from porcine adrenal microsomes. Comparison of the first 99 amino acid residues of both sequences revealed three substitutions comprising two leucine residues in positions 10 and 13, and one arginine residue in position 55 for our sequence, instead of threonine in position 10 and lysine in position 13 and 55 for the isolated enzyme. A swine homologous probe was derived from the isolated 21-hydroxylase gene and used for gene assignment by RFLP studies in two swine leucocyte antigen (SLA) informative families. The results demonstrate that the swine 21-hydroxylase gene is located within or close to the swine MHC. Taken together, the present results suggest the existence of a single 21-hydroxylase gene per haploid genome.

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.

Associations of major histocompatibility complex haplotypes with body weight and egg production traits in S1 White Leghorn chickens

Body weights at 8, 20, and 32 wk, total egg production, average egg weight, egg production during a 4-wk period, and age at first egg laid were measured in 652 female progeny of heterozygous x heterozygous (F1) or heterozygous x homozygous (backcross) matings of the Iowa State University S1 White Leghorn chicken line. Hens were classified by B-haplotypes (B1 or B19) and haplotype-associated immune responses (high or low) to the amino acid polymer glutamic acid-alanine-tyrosine (Ir-GAT). Body weights were affected by parental mating group, sire, and dam, but they were not affected by haplotype (B/Ir-GAT). Sexual maturity and egg production were not affected by any factors except hatch. Average egg weight was affected by parental mating group, sire, dam, and genotype, with homozygous B19B19 birds having a heavier mean egg weight (41.71 g +/- .20) than homozygous B1B1 Ir-GAT-high and - low birds (40.8 g +/- .38 and 39.2 g +/- .54, respectively); mean egg weights of heterozygous birds were approximately intermediate to the others.

The influence of the BoLA-A locus on reproductive traits in cattle

Associations between the major histocompatibility complex (MHC) and reproductive performance have been reported in humans, mice, rats, pigs and chickens. Only the A locus of the bovine major histocompatibility complex (BoLA-A) has been well characterized, and 42 alleles of this locus have been identified in American cattle. Four studies were conducted to examine the association between alleles of the BoLA-A locus and reproductive performance. Testis size, which is an indicator of early puberty and increased fertility in young bulls, was examined in 440 yearling bulls from nine breeds with a gene substitution model that included the effects of breed, sire, age of dam and age or weight of the bull. Estimated breeding value for twinning was examined with a gene substitution model with 204 cattle from a herd with a high frequency of twinning. Fertility of potential partners having BoLA-A locus alleles in common was examined in a prospective study involving 101 pure-bred Hereford cows mated by artificial insemination to four pure-bred Hereford bulls. The effect of homozygosity on birth weight, preweaning weight gain and post-weaning weight gain was estimated in a sample of 683 calves from nine breeds; 22% of the calves were apparently homozygous and 78% were heterozygous at the BoLA-A locus. There were significant and large effects of some BoLA-A locus alleles on paired testicular volume, but the analyses on the other traits did not show significant associations. Substitution of the W6.1 allele for the W9A allele reduced paired testicular volume by 150 +/- 44 cm3. The W6.1 allele has now been shown to influence a reproductive trait, a production trait and susceptibility to an economically important disease. Selection for these traits may influence the frequency of the large number of alleles at the BoLA-A locus.

Influence of the swine major histocompatibility complex on reproductive traits in miniature swine

Three swine leukocyte antigen (SLA)-defined strains of miniature swine and one recombinant strain were examined to evaluate the influence of the SLA Complex on litter size and piglet survivability. To separate the effects of sire and dam SLA haplotype from other sire and dam effects, a general linear model was employed to analyse data from 58 litters. Analysis of variance showed that sire and dam haplotype each contributed significantly to the variability observed in litter size among the sire and dam SLA combinations examined (P less than 0.0001, P less than 0.05, respectively). Sow SLA-haplotype as well as sire and dam effects other than those related to haplotype were significant factors contributing to survival until weaning (8 weeks) (P less than 0.10, P less than 0.07, P less than 0.001, respectively), but sire SLA-haplotype did not contribute significantly to this trait. Expected and observed haplotype frequencies of offspring in each litter were compared using chi-square analysis. A discrepancy was observed only in offspring from SLAa/d by SLAa/d matings, for which significantly fewer SLAa/a piglets were weaned than expected (P less than 0.06). Laparotomy during day 35-50 of pregnancy suggested that litter size was not an accurate estimate of ovulation rate and that ovulation rate was similar for dams of ad, ac and dd haplotypes.

Research note: differences in major histocompatibility complex gene frequencies associated with feed efficiency and laying performance

Associations between egg production and feed efficiency and the genes of the major histocompatibility complex (MHC) of the chicken were investigated. Breeders were selected on the basis of indexes incorporating information on body weight and egg mass, with or without feed consumption information. Over 1,000 progeny were serotyped for the erythrocyte antigen B (Ea-B) after the 6th generation of selection. The B2 and B13 haplotypes accounted for over 75% of the Ea-B gene pool in all lines. Comparing each index-selected line with the control B2 significantly increased in frequency at the expense of B13. This study further implicates MHC-linked genes as important in the physiology of growth and reproduction in the chicken.

Influence of the major histocompatibility complex on disease resistance and productivity

Publications in which chickens of different B haplotypes were studied for differences in disease resistance or productivity traits are reviewed. The most prominent effects on diseases are those involving tumors, but other examples involving autoimmune disease and microbial infections not resulting in neoplasia or autoimmunity are also cited. Each referenced disease paper is briefly defined with regard to: population used, B alleles present, and the most resistant B types. Studies citing B haplotype influences on productivity and reproductive fitness traits are summarized and the most desirable B genes in each referenced population are given. Plausible mechanisms of the B haplotype's influence on the traits are briefly discussed. Based on the evidence reviewed for disease resistance and productivity traits and the central role of B-complex genes in immune function, it is concluded that poultry breeders should develop B-genotype information in their base breeding populations and use those types yielding optimal performance.

Effect of swine lymphocyte antigen haplotypes on birth and weaning weights in pigs

Birth weights of 708 live piglets and weaning weights of 566 piglets were used to investigate the effect of the swine lymphocyte antigen (SLA) complex on these traits in Large White pigs. Piglets were from litters of a long-term selection experiment to measure response for selection to increase litter size. SLA haplotypes were determined using conventional class I antisera. A total of 14 haplotypes were detected. The effect of SLA haplotype on birth and weaning weights was investigated using a statistical model that included the effects of experimental group, sire, dam, sex and SLA haplotype. Results indicated that SLA class I haplotype 13.1.3 increased birth weights (P less than 0.10) and significantly increased weaning weights (P less than 0.01). This effect of haplotype 13.1.3 on weaning weight was 605 +/- 215 g (0.3 standard deviations). SLA class I homozygosity did not appear to affect birth and weaning weights. These results suggest that the SLA complex plays an important role in early growth in the pig and that further study of SLA effects on growth and reproduction are warranted.

Effect of absorbed and nonabsorbed anti-H-2 antiserum on mouse blastocysts

Conventional antisera and monoclonal antibodies have been used to demonstrate the presence of H-2 antigens on preimplantation mouse embryos. In this study, the specificity of previously used anti-H-2 conventional antisera was tested by absorption of the antisera on spleen lymphocytes. It was found that absorption of the anti-H-2 antisera removed all of the antibody reactive with lymphocytes, but only about half of the antibody reactive with embryos. The effect of absorbed and nonabsorbed anti-H-2 antisera on mouse blastocysts was tested both by cytotoxicity assays and by electron microscopy. The results suggest that conventional antisera do indeed detect H-2 antigens on mouse embryos, but they may detect other, as yet undefined, antigens as well.

Possible roles of compound membrane receptors in the immune system

A compound receptor is defined as a molecular complex which attains its final, biologically active structure by rearrangement and assembly in the membrane of several structural subunits. The existence of such receptor complexes is strongly suggested by experiments which demonstrated a very close association between certain ligand (primarily insulin) receptors and the major histocompatibility complex (MHC) antigens. We present here speculations on the possible role of MHC as a structural part of a multitude of receptors with different biological functions, and we argue that recent immunological data on minor histocompatibility antigens, antigen-presenting cells and T-lymphocyte receptors fit into this hypothesis.

The MHC haplotypes of the chicken

The major histocompatibility complex (MHC) of Gallus gallus is the B complex of which three classes of cell-membrane antigens have been clearly defined by serological, histogenetic, and biochemical methods. Two of these classes are homologous to classes I and II of mammals (B-F and B-L, respectively), while the third (B-G) is a differentiation antigen of the erythroid cell-line; the mammalian homologue of this class is still undefined. The B haplotypes comprise at least one gene of each class that displays linkage disequilibrium of a remarkable strength. The present work is the first systematic comparison by serological and histogenetic methods of the allelic products (allomorphs) of 15 haplotypes, including all of the 11 that were accepted as "standard" B haplotypes at the recent international Workshop on the chicken MHC in Innsbruck, Austria. The analysis has revealed many similarities, but only four pairs of probable identities: G2 and G12, F4 and F13, L4 and L13, L12 and L19. It appears therefore that the B-G locus is comparable in its degree of polymorphism to the class I (B-F) locus. The "standard" haplotypes are almost all of White Leghorn derivation, and preliminary typings of other breeds of chickens, and of wild chickens, indicate the existence of a much wider spectrum of allomorphs.