Comparative organization and function of the major histocompatibility complex of domesticated cattle.

This review focuses on recent advances in research on the bovine major histocompatibility complex (BoLA), with specific reference to the genetic organization, polymorphism and function of the class II genes. The BoLA region is unlike the MHC of humans and mice in that a large inversion has moved several class II genes, including the TAP/LMP cluster, close to the centromere of bovine chromosome 23. Therefore, close linkage of MHC genes and other genes associated with the MHC in humans and mice does not appear to be required for normal immunological function. In cattle, polymorphism in the class IIa genes influences both the magnitude and the epitope specificity of antigen-specific T-cell responses to foot-and-mouth disease virus peptides. Disease association studies have demonstrated that BoLA alleles affect the subclinical progression of bovine leukemia virus (BLV) infection. This association is strongly correlated with the presence of specific amino acid motifs within the DRB3 antigen-binding domain. In addition to the practical significance of these findings, the association between BoLA and BLV provides a unique model to study host resistance to retrovirus infection in a non-inbred species. These studies contribute to our understanding of the evolution of the MHC in mammals, to the development of broadly effective vaccines, and to breeding strategies aimed at improving resistance to infectious diseases.