Molecular Immunogenetics in Susceptibility to Bovine Dermatophilosis

To identify molecular genetic markers of resistance or susceptibility to dermatophilosis in cattle, we used a functional candidate gene approach to analyse the DNA polymorphisms of targeted genes encoding molecules implicated in known mechanisms of both non-specific and specific immune responses existing in the pathogen/host interface mechanisms. The most significant results were obtained within the Major Histocompatibility Complex (MHC) where the BoLA-DRB3 and DQB genes encode molecules involved in the antigen presentation to T cell receptors. A unique particular BoLA class II haplotype, constituted by one DRB3 exon 2 allele and one DQB allele highly correlates with the susceptibility character (P < 0.001). This marker of susceptibility haplotype was also found and validated in other bovine populations. A eugenic marker assisted selection was developed in the field by eliminating only the animals having this haplotype of susceptibility. Then the disease prevalence was reduced from 0.76 to 0.02 over 5 years. A crossbreeding plan is in progress to study the genetic transmission of the genotypic and phenotypic characters of susceptibility to dermatophilosis. In conclusion, we discuss several hypothesis at the molecular and cellular levels to better define the exact role of the MHC molecules in the diseases control and to answer the question. how MHC diversity is selectively maintained by natural selection imposed by the pathogens? (Resume d'auteur)