BoLA class II polymorphism and immune response to Mycobacterium bovis antigens in vitro

In a sample of 47 Holstein-Friesian calves, experimentally sensitized in vivo with a suspension of killed Mycobacterium bovis the BoLA class-II polymorphism was analysed at the DQA, DQB, and DRB loci to define its role in the specific immune response. Lymphocyte proliferation under PPD stimulation, phagocytosis of killed M. bovis cells, and the humoral response to PPD antigens, tested by ELISA, were performed in vitro 21 days after sensitization to evaluate the specific immune response. All the animals responded well to the immune test. The humoral response was only slightly affected by some alleles in the D subregions investigated. Lymphocyte proliferation was significantly, and positively, affected by DQA*5, DQB*5, and DRB*5B+5C of the linkage group DH*18A. In particular, the effect of DRB*5C alone was more than two times higher than the standard deviation. Phagocytosis was significantly and negatively affected by DQA*9B and DQB*9B of the linkage group DH*22B, and also by DQA*1A, DQB*1, and DRB*1A of the linkage group DH*24A. In these specific experimental conditions, the results demonstrate that the humoral response is only slightly under the control of some class-II alleles, while lymphocyte proliferation and phagocytosis are affected. The DRB locus shows a major effect on lymphocyte proliferation.