Marek's disease and major histocompatibility complex haplotypes in chickens selected for high or low antibody response

Growth of White Leghorn Chicken Immune Organs after Long-Term Divergent Selection for High or Low Antibody Response to Sheep Red Blood Cells

Long-term divergent selection from a common founder population for a single trait-antibody response to sheep erythrocytes 5 days post-injection-has resulted in two distinct lines of White Leghorn chickens with a well-documented difference in antibody titers: high (HAS)- and low (LAS)-antibody selected lines. Subpopulations-high (HAR)- and low (LAR)-antibody relaxed-were developed from generation 24 of the selected lines to relax selection. The objective of the current experiment was to determine if this long-term selection and relaxation of selection impacted the growth of two organs important to chicken immunity: the spleen and the bursa of Fabricius. Spleens and bursae were obtained from ten chickens per line at nine timepoints (E18, D0, D6, D13, D20, D35, D49, D63, and D91) throughout their rapid growth phase and presented as a percent of body weight. Significance was set at p ≤ 0.05. For the spleen, all lines consistently increased in size relative to body weight to D49, followed by a consistent decline. All lines had a similar growth pattern, but HAS spleens grew faster than LAS spleens. For the bursa, LAS was smaller than the other three lines as an embryo and also smaller than HAS through D63. In the selected lines, bursa weight peaked at D35, whereas the relaxed lines peaked at D49. By D91, there was no difference between lines. Artificial and natural selection, represented by the long-term selected and relaxed antibody lines, resulted in differences in the growth patterns and relative weights of the spleen and bursa of Fabricius.

Association of MHCY genotypes in lines of chickens divergently selected for high or low antibody response to sheep red blood cells

The chicken MHCY region contains members of several gene families including a family of highly polymorphic MHC class I genes that are structurally distinct from their classical class I gene counterparts. Genetic variability at MHCY could impart variability in immune responses, but robust tests for whether or not this occurs have been lacking. Here we defined the MHCY genotypes present in 2 sets of chicken lines selected for high or low antibody response, the Virginia Tech (VT) HAS and LAS, and the Wageningen University (WU) HA and LA lines. Both sets were developed under long-term bidirectional selection for differences in antibody responses following immunization with the experimental antigen sheep red blood cells. Lines in which selection was relaxed (VT HAR and LAR) or lacking (WU C) provided controls. We looked for evidence of association between MHCY genotypes and antibody titers. Chickens were typed for MHCY using a recently developed method based on a multilocus short tandem repeat sequence found across MHCY haplotypes. Five MHCY haplotypes were found segregating in the VT HAS and LAS lines. One haplotype was present only in HAS chickens, and another was present only in LAS chickens with distribution of the remaining 3 haplotypes differing significantly between the lines. In the WU HA and LA lines, there was a similar MHCY asymmetry. The control populations lacked similar asymmetries. These observations support the likelihood of MHCY genetics affecting heritable antibody responses and provide a basis for further investigations into the role of MHCY region genes in guiding immune responses in chickens.

Association of LEI0258 Marker Alleles and Susceptibility to Virulent Newcastle Disease Virus Infection in Kuroiler, Sasso, and Local Tanzanian Chicken Embryos

Newcastle disease (ND) control by vaccination and an institution of biosecurity measures is less feasible in backyard chicken in developing countries. Therefore, an alternative disease control strategy like the genetic selection of less susceptible chicken genotypes is a promising option. In the present study, genetic polymorphism of LEIO258 marker and association with susceptibility to virulent Newcastle disease virus (NDV) infection in Kuroilers, Sasso, and local Tanzanian chicken embryos were investigated. Samples from high (15%) and less (15%) susceptible cohorts were genotyped by sequencing of LEI0258 marker. A total of 75 DNA sequences comprised of 29 Kuroiler, 29 local Tanzanian chickens, and 17 Sasso were analyzed. Neighbor-joining phylogenetic trees were constructed to depict the clustering of LEI0258 marker alleles and relationship with susceptibility. Alleles with frequency ≥3 were considered for association with susceptibility by the use of the inference technique. The present findings suggest that some LEI0258 marker genetic polymorphisms apart from LEI0258 marker allelic based on sizes may be linked with chicken MHC-B haplotypes that confer chickens variability in resistance or susceptibility to infections. Furthermore, these results demonstrate the presence of relationship between LEI0258 marker polymorphisms and variations in chicken susceptibility to NDV infection, which could be utilized in breeding programs designed to improve chicken disease resistance.

Parent-of-origin has no detectable effect on survival days of Marek's disease virus infected White Leghorns

Marek's Disease (MD) is a neoplastic disease of chickens and remains as a chronic infectious disease that threatens the poultry industry. Improving genetic resistance to MD in poultry is an important long-term goal, which would significantly augment the current control measures against MD and eventually reduce the annual economic loss. In this study, survival patterns of F2 birds from 2 reciprocal crosses were compared to examine possible difference in survival between the reciprocal crosses in response to MD virus (MDV) challenge. A total of 246 and 224 F2 chicks derived from reciprocal crosses of lines 63 × 72 and lines 72 × 63, respectively, were sampled from an MDV challenge trial and survival days were recorded from the MDV-inoculation date to the end of experiment. Statistical analyses, including Principal Component Analysis (PCA) followed by a cox-regression model, showed there was no significant difference in survival days between reciprocal crosses (P > 0.05). To the best of our knowledge, this is the first MD survival study on reciprocal crosses of 2 genetically diversified lines of chickens differing in MD resistance. This report documented the experimental evidence that the genetic lineage of grandparental (maternal or paternal) effect on survival days was minimal, if present at all.

Evolutionary analyses of non-genealogical bonds produced by introgressive descent

All evolutionary biologists are familiar with evolutionary units that evolve by vertical descent in a tree-like fashion in single lineages. However, many other kinds of processes contribute to evolutionary diversity. In vertical descent, the genetic material of a particular evolutionary unit is propagated by replication inside its own lineage. In what we call introgressive descent, the genetic material of a particular evolutionary unit propagates into different host structures and is replicated within these host structures. Thus, introgressive descent generates a variety of evolutionary units and leaves recognizable patterns in resemblance networks. We characterize six kinds of evolutionary units, of which five involve mosaic lineages generated by introgressive descent. To facilitate detection of these units in resemblance networks, we introduce terminology based on two notions, P3s (subgraphs of three nodes: A, B, and C) and mosaic P3s, and suggest an apparatus for systematic detection of introgressive descent. Mosaic P3s correspond to a distinct type of evolutionary bond that is orthogonal to the bonds of kinship and genealogy usually examined by evolutionary biologists. We argue that recognition of these evolutionary bonds stimulates radical rethinking of key questions in evolutionary biology (e.g., the relations among evolutionary players in very early phases of evolutionary history, the origin and emergence of novelties, and the production of new lineages). This line of research will expand the study of biological complexity beyond the usual genealogical bonds, revealing additional sources of biodiversity. It provides an important step to a more realistic pluralist treatment of evolutionary complexity.

Ecological immunology: costly parasite defences and trade-offs in evolutionary ecology

In the face of continuous threats from parasites, hosts have evolved an elaborate series of preventative and controlling measures - the immune system - in order to reduce the fitness costs of parasitism. However, these measures do have associated costs. Viewing an individual's immune response to parasites as being subject to optimization in the face of other demands offers potential insights into mechanisms of life history trade-offs, sexual selection, parasite-mediated selection and population dynamics. We discuss some recent results that have been obtained by practitioners of this approach in natural and semi-natural populations, and suggest some ways in which this field may progress in the near future.

MHC class I variation associates with parasite resistance and longevity in tropical pythons

Using restriction fragment length polymorphism (RFLP) we identified 26 unique major histocompatibility complex (MHC) genotypes in 104 water pythons. We observed a significant independent association between reduced blood parasite load (Hepatozoon sp.) and python body length/age, presence of a specific RFLP fragment (C-fragment) and the overall number of fragments. The parasite has a negative impact on several python life-history traits such as growth, nutritional status and longevity. Thus, the C-fragment could be considered a 'good gene' (a fitness-enhancing genetic element). However, while the number of fragments affected parasite load, the association between level of parasitaemia and fragment number was not linear, and, hence, minimum parasite infection level was achieved at an intermediate number of fragments. Intermediate MHC fragment numbers were also observed among the largest/oldest pythons, suggesting that both a specific fragment and intermediate levels of MHC polymorphism enhanced python longevity. Thus, our results suggest python MHC is subject to both frequency-dependent and balancing selection.

Effect of human leukocyte antigen heterozygosity on infectious disease outcome: the need for allele-specific measures

BACKGROUND

Doherty and Zinkernagel, who discovered that antigen presentation is restricted by the major histocompatibility complex (MHC, called HLA in humans), hypothesized that individuals heterozygous at particular MHC loci might be more resistant to particular infectious diseases than the corresponding homozygotes because heterozygotes could present a wider repertoire of antigens. The superiority of heterozygotes over either corresponding homozygote, which we term allele-specific overdominance, is of direct biological interest for understanding the mechanisms of immune response; it is also a leading explanation for the observation that MHC loci are extremely polymorphic and that these polymorphisms have been maintained through extremely long evolutionary periods. Recent studies have shown that in particular viral infections, heterozygosity at HLA loci was associated with a favorable disease outcome, and such findings have been interpreted as supporting the allele-specific overdominance hypothesis in humans.

METHODS

An algebraic model is used to define the expected population-wide findings of an epidemiologic study of HLA heterozygosity and disease outcome as a function of allele-specific effects and population genetic parameters of the study population.

RESULTS

We show that overrepresentation of HLA heterozygotes among individuals with favorable disease outcomes (which we term population heterozygote advantage) need not indicate allele-specific overdominance. On the contrary, partly due to a form of confounding by allele frequencies, population heterozygote advantage can occur under a very wide range of assumptions about the relationship between homozygote risk and heterozygote risk. In certain extreme cases, population heterozygote advantage can occur even when every heterozygote is at greater risk of being a case than either corresponding homozygote.

CONCLUSION

To demonstrate allele-specific overdominance for specific infections in human populations, improved analytic tools and/or larger studies (or studies in populations with limited HLA diversity) are necessary.

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.

Sex differences in the resistance of turkeys to Escherichia coli challenge after immunosuppression with dexamethasone

Five-week-old male and female commercial turkeys were immunosuppressed with two levels of dexamethasone (DEX) and challenged by airsac inoculation with 100 cfu of Escherichia coli. Mortality and airsacculitis (AS) scores were significantly higher in challenged birds treated with DEX and marginally higher in males than in females. Male mortalities had significantly higher AS scores than females. Recovery of E. coli from blood and tissues was significantly higher in challenged birds treated with DEX, marginally higher in males (P = 0.09), and significantly higher in male mortalities than in female mortalities. The low level of DEX seemed to have a protective effect against bacterial challenge in males, whereas the high level of DEX had a more adverse effect in males than in females. Body weights 2 wk postchallenge were significantly decreased by both DEX and E. coli, challenge. Relative liver and heart weights were increased by both DEX and E. coli, challenge, whereas bursal:spleen ratios were decreased by both treatments. Total leukocyte counts and relative heterophil counts from blood samples taken 24 h postinfection were significantly higher in DEX-treated birds and in unchallenged DEX-treated females than in males. The DEX treatment resulted in significantly higher heterophil:lymphocyte ratios, but there was no difference between sexes. Males had significantly lower serum levels of uric acid, total protein, albumin, aspartate aminotransferase, and lactate dehydrogenase than did females. Dexamethasone treatment also resulted in lower levels of total protein, albumin, and aspartate aminotransferase. These data suggest that male turkeys may be more susceptible to colisepticemia than female turkeys, especially when under severe stress.

Immunoresponsiveness in chickens: association of antibody production and the B system of the major histocompatibility complex

Lines of White Leghorn chickens were selected for high or low antibody response to sheep erythrocytes for five generations. The base population from which the experiment started was composed of individuals all of which were heterozygous at the MHC haplotypes B13 and B21. Body weights, egg production traits, and genotypes at the B system were monitored for all individuals in each generation. By Generations 4 and 5 there was separation of the two replicate lines selected for high titer from the two replicate lines selected for low titer. Over the course of the experiment, higher antibody titers and lower BW were associated with B21 and lower antibody titers and higher BW were associated with B13, although these relationships did not occur in every instance. Conclusions were that the B system was associated with antibody response, but that the chickens did not depend entirely upon that association for protection against foreign proteins. Also, the importance of having replicate lines in a selection experiment was shown.

Frequencies and genetic diversity of major histocompatibility complex class II haplotypes in commercial turkey lines

The purpose of the present study was to estimate frequencies and diversity of MHC haplotypes in primary breeding lines of commercial turkeys. Restriction fragment length polymorphism analysis was used to assay MHC Class II haplotypes of blood samples from 11 primary breeding lines (comprised of both sire and dam lines) contributed by three major turkey breeding companies. Twenty-five blood samples obtained from wild turkeys were included for comparison. Seven haplotypes previously identified in experimental turkey lines were detected in the commercial lines. One haplotype, A, was predominant in all commercial lines with an average frequency of 76% and in the wild turkeys with a frequency of 46%. Diversity of MHC haplotypes was reduced in the commercial lines compared with the wild turkey. Seven commercial lines had no more than four haplotypes and loci in some lines were close to fixation. Haplotypic frequencies among sire and dam lines differed significantly, but genetic diversity was not different. Only Haplotype D was significantly more frequent in sire than in dam lines. The present data demonstrate that genetic diversity at MHC loci was low in commercial turkey lines.

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.

Evaluation of resistance of four strains of commercial laying hens to experimental infection with Salmonella enteritidis phage type eight

Four different strains of White Leghorn hens were orally infected with 1 x 10(8) cfu of Salmonella enteritidis phage Type 8 per bird. The birds were monitored for 10 wk postinfection for colonization of internal organs, fecal shedding of S. enteritidis, and the production of S. enteritidis-contaminated eggs. There was no difference among the four hen strains in regards to the probability of S. enteritidis isolation from liver and spleen, ovary, and cecal tissue within the first 30 d postinfection. However, during the first 14 d postinfection, S. enteritidis organisms were isolated in significantly higher rates from eggs and fecal samples of Strain A than from samples obtained from the other three hen strains. Results suggest that there may be inherent differences between strains of laying hens with regard to their response to infection with S. enteritidis.

High and low responsiveness to vaccines in farm animals

Low responsiveness in some farm animals is emerging as a problem in the application of newly developed vaccines which operate at skin surfaces and mucous membranes. Breeding for resistance to specific diseases seems to be associated with breeding for specific immune responsiveness in farm animals and very likely this involves selection for major histocompatibility complex (MHC) haplotype. However, other factors contribute to low responsiveness and these include poor nutrition, sire effects, antigenic competition and inadequate effector mechanisms. The future of newly developed vaccines will rest on the solution to the low responder problem, and once solved, the application of these vaccines will be fully utilized for disease control in farm animals.

Differences between genetic stocks of chickens in response to acute and delayed effects of an organophosphorus compound

The influence of genotypes of the major histocompatibility complex (MHC) on susceptibility to acute and delayed effects of an organophosphorus ester was measured in adult White Leghorn chickens from lines differing in response to sheep red blood cell (SRBC) antigen. Chickens from lines selected for high (HA) or low (LA) antibody response to SRBC and homozygous for B13B13 or B21B21 genotypes at the MHC were administered a single subcutaneous injection of diisopropyl phosphorofluoridate (DFP) at dosages of 0, 0.25, 0.50, or 1.0 mg/kg body weight using corn oil as the carrier. Criteria for toxicological responses included clinical, biochemical, and pathological measures. Clinical signs of acute cholinergic poisoning and delayed neuropathy were dose related. Brain and blood cholinesterase and carboxylesterase activities were more sensitive to inhibition by DFP than were liver cholinesterase and carboxylesterase activities. Cholinergic signs 3 h after administration of DFP were more pronounced in line HA than in line LA chickens. Pathological evidence of delayed neuropathy 2 wk after DFP administration was also more evident in HA than LA chickens. Although less pronounced than that for lines, differences in neurotoxic manifestations following DFP administration were greater for chickens of B21B21 than B13B13 genotypes. Activity of A-esterases, which hydrolyze organophosphorus esters without being inhibited by them, was lower in plasma of line HA than line LA chickens. Differences among the genotypes in activity of other esterases were not found in chickens not receiving DFP. These results indicated that responses of chickens to the neurotoxicant DFP were influenced by the background genome of the chickens.

Research note: resistance of chickens to an outbreak of necrotic enteritis as influenced by major histocompatibility genotype and background genome

An outbreak of necrotic enteritis occurred in chickens that were B13B13 or B21B21 at the MHC in sublines of lines selected for high (HA) and low (LA) antibody response to sheep erythrocytes. Percentage mortality and hen-day egg production, although similar for both background genomes, were different for MHC genotypes. Mortality was 6% for B21B21 and 15% for B13B13 types. Although hen-day egg production for both types declined from about 76 to 50%, the decrease occurred earlier but recovery of survivors was faster in B13B13 than in B21B21 pullets.

Evaluating linkage between DNA fingerprint bands and quantitative traits in chickens: interactions

This study assessed the influence of background genome on expression of genes linked to DNA fingerprint (DFP) bands in chickens. Two experimental lines of White Plymouth Rocks previously selected for high or low 8-wk body weight were crossed to produce two F1 males that served as heads of two sire families. Each of these sires was mated to three hens from an unrelated White Leghorn population to produce progeny in which quantitative traits of 4-, 8-, and 12-wk body weight and shank length at 12 wk were measured. The DFP patterns were produced for all individuals in the study. For the 12 sire-specific DFP bands (common to both F1 sires but not found in the dams), each offspring was classified as having or not having each band. Then, an analysis of variance was conducted for each DFP sire band with sex, hatch, dam family, and presence or absence of the sire band as main effects. Interactions between dam family and presence or absence of sire band were also tested. Of 48 possible analyses of variance (12 sire bands by 4 quantitative traits), 3 resulted in significant effects due to sire band, and 2 indicated significant interactions. Thus, associations of a DFP band and a gene coding for a quantitative trait were present, but, in some cases, the expression of the trait differed, depending on the dam family in which it occurred. These data suggest that associations between DFP bands and quantitative traits may not be consistent in different genetic backgrounds.

Effect of divergent selection for immune responsiveness and of major histocompatibility complex on resistance to Marek's disease in chickens

Lines of chickens selected for nine generations for high (H) or low (L) antibody response to SRBC, a randombred control (C) line, and an F1 cross between H and L lines were challenged for resistance to Marek's disease (MD). Hens only were challenged at day-old by contact with virulent MD Strain K. Birds were serologically typed for MHC erythrocyte antigens. Chicks from the L and H lines died earlier and later, respectively, than the C chicks, whereas time of death did not differ between F1 birds and the L chicks. Mortality in the L line (70.1%) was higher than in the C line (42.8%), but mortality in the H line (40.9%) was not lower than in the C line or the F1 cross (47.5%). Effects of MHC genotypes and haplotypes on mortality from MD were estimated within lines with a logistic regression model. Effect of MHC was moderate in the H line (P < .10) and highly significant in the C line (P < .005). Effects of MHC genotypes were similar in the H and C line but differed in the L and F1. Heritability of mortality from MD estimated with a threshold model including relationships between individuals was .40 when all lines were grouped together, whereas heritability estimated for each line separately was .45, .51, and .78 in the H, C, and L lines, respectively. Correlations between estimated breeding values for antibody response to SRBC and mortality from MD varied between lines and sexes. Correlations also were affected by whether or not the MHC effect was taken into account.

Antibody responses to combinations of antigens in white Leghorn chickens of different background genomes and major histocompatibility complex genotypes

Antibody responses in chickens to SRBC, Newcastle disease (NDV), and Brucella abortus (BA) were compared when given singly or in combination. Chickens used in the present experiment originated from a cross and then backcrossing of White Leghorn populations that had been selected for high (HA) or low (LA) antibody response to SRBC antigens. The populations used in the current study were segregating for MHC haplotypes B13 and B21. The experiment had a 2 x 3 x 6 factorial arrangement of treatments (two background genomes: HA and LA; three MHC haplotypes: B13B13, B13B21, and B21B21; and six antigen treatments: SRBC, NDV, or BA only, SRBC plus NDV, SRBC plus BA, and NDV plus BA). Antigens were administered either i.v. (SRBC) or i.m. (NDV and BA) when chicks were 42 days of age. Blood was obtained 27 days later (69 days of age) for antibody determinations. A significant background genome by MHC haplotype interaction for BA antibodies was due to relatively high titers in Line HA chickens of MHC genotypes B13B13 and B13B21. Background genome by MHC genotype interactions were not significant for SRBC or NDV antibodies. Antibody titers to SRBC were higher in background genome HA than LA, and similar among MHC genotypes. Antibodies to NDV were lower in chickens of MHC genotype B21B21, but there were no differences due to background genome. For each of the three antigens, antibody responses were highest when administered singly rather than in combination. Antibody titers were lower for SRBC when given with BA, and for BA titers when given with NDV.(ABSTRACT TRUNCATED AT 250 WORDS)