BACKGROUND: Major histocompatibility complex (MHC) plays a central role in regulation and control of the immune responses to infectious diseases. Due to its polymorphism, individual differences in response to vaccines have been observed in different chicken populations. Studying the association of chicken MHC with immune response to vaccines will help the control of infectious disease and vaccination success. Objectives: The present study aimed to evaluate the MHC polymorphism and its association with antibody response against infectious bursal disease (Gumboro), Newcastle (ND) and Influenza (AI) vaccines in Khorasan native chickens. Methods: Diversity of LEI0258 microsatellite marker (MHC genotyping) was investigated by fragment analysis method. Antibody titer against IBD was measured by ELISA and antibody titers against ND and AI vaccines were measured by Haemaglutination Inhibition (HI) assay. Statistical analysis was performed using SPSS software (version 21). Univariate regression analysis was performed using weighted least squares with weight number of progeny mean data. Results: Total of 13 LEI0258 microsatellite alleles were identified in Khorasan native chickens which indicated a high genetic diversity in the population. The allele 361 bp had the highest (28.48%) and the allele 350 bp had the lowest (0.69%) frequency, respectively. In evaluating the association of MHC with immune responses, 311 and 313 bp alleles were significantly associated with elevated immune responses to Newcastle vaccine, while allele 266 bp was associated with lower IBDV antibody titers (p<0.05). ConclusionS: According to the important role of MHC in controlling infectious disease resistance or susceptibility and quality of immune responses, these results could be used for selection and improving the populations under selective breeding.

BACKGROUND: Major histocompatibility complex (MHC) encodes for highly variable molecules, most of which are responsible for foreign antigen recognition and activation of immune responses in the host. LEI0258 microsatellite, located in the poultry MHC region, is a suitable genetic marker for determining MHC haplotypes and genetic diversity in poultry.OBJECTIVES: Considering the fact that there is no report on the frequency and types of MHC alleles and population genetic analysis in Ross 308 poultry in Iran, the present study aimed to investigate the diversity of MHC haplotypes of Ross 308 broilers by LEI0258 microsatellite.METHODS: A total of 216 blood samples were collected from two productive herds of Ross 308 broilers. After extracting DNA of the blood samples and amplifying LEI0258 microsatellite alleles, genotyping of MHC haplotypes was performed using agarose gel electrophoresis and fragment analysis techniques.RESULTS: A total of seven alleles and 21 genotypes were identified for LEI0258 microsatellite in these two groups. the highest and the lowest frequencies belonged respectively to allele 385 bp (42.86 %) and allele 300 bp (4.33 %). Heterozygous 207/385 was found to be the dominant genotype in both populations. According to the similarity matrix analysis, there was an 84.56 % similarity between the two groups.CONCLUSIONS: The results obtained in this study revealed a high level of heterozygosity (85.71 % and 91.35 %) and deviation from Hardy–Weinberg equilibrium (P<0.0001) in these two Ross populations. Ross 308 broiler chickens had lower allelic diversity and higher genetic similarity compared to the native ones. These findings provided additional information on the use of MHC as a candidate gene marker in genetic improvement and resource conservation in broiler populations.