A single amino acid deletion in the antigen binding site of BoLA-DRB3 is predicted to affect peptide binding

Two bovine MHC class II alleles, BoLA-DRB3∗0201and BoLA-DRB3∗3301, contain a three base pair deletion which results in the deletion of a lysine (Kβ65) in the antigen recognition site (ARS). Modelling of BoLA-DRB3∗0201 with the conserved lysine Kβ65 and BoLA-DRB3∗0201 without Kβ65 indicated that this deletion altered the peptide specificity of the ARS, and may impact on the immune response. To test this hypothesis, the presence of Kβ65 was analysed in a sample of cattle vaccinated with the commercial cattle tick vaccine (TickGARD). Homozygous deletion of Kβ65 was significantly associated with high response to TickGARD (P<0.05). Screening of the TickGARD antigen identified a potential T cell epitope that is recognised better by animals that are homozygous for the Kβ65 deletion. This study provides evidence that changes in the ARS of MHC class II molecules may be associated with the well recognised animal to animal variation in magnitude of vaccine response.