Effect of genetic variation in the MHC Class II DRB region on resistance and susceptibility to Johne’s disease in endangered Indian Jamunapari goats

Abstract

The pathogenesis of Johne's disease (JD), caused by Mycobacterium avium subsp. paratuberculosis (MAP), is complex and has not been completely understood yet. In the present study, we analysed the polymorphism in the exon-2 of the caprine major histocompatibility complex (MHC) Class II DRB region and its association with resistance or susceptibility to JD. A total of 203 Jamunapari goats, which is an Indian endangered breed highly susceptible to JD, kept at a single farm were studied. On the basis of clinical signs, microscopic examination, faecal culture, ELISA and diagnostic PCR, 60 and 143 goats were classified as resistant and susceptible to JD, respectively. PCR-based restriction fragment length polymorphism (PCR-RFLP) with two enzymes, PstI and TaqI, was used to assess variation in the DRB gene(s) in all 203 goats studied. Two di-allelic single nucleotide polymorphisms (SNPs), here referred as 'P' and 'T', were tested. In each of them, three genotypes were found in the group analysed. The minimum allele frequencies (MAFs) were 0.233 and 0.486 for the P and T SNPs, respectively. Statistically significant associations between alleles, individual genotypes and composed genotypes of both SNPs were found. The frequency of p and t alleles, of individual pp and tt and of composed pptt genotypes were significantly higher (P(corr) < 0.001) in the 'resistant' group as compared to the 'susceptible' group, while the P and T alleles were associated with susceptibility (P(corr) < 0.001). In heterozygous genotypes, susceptibility was dominant over resistance. The effects of both SNP on resistance and susceptibility were comparable and composed heterozygous genotypes showed intermediate levels of susceptibility in terms of the odds ratio and P-values calculated.