Association of bovine major histocompatibility complex class I (BoLA-A) alleles with immune response to Brucella abortus strain 19 in calves.

In the present study, we analyzed the immune response of calves to Brucella abortus strain 19 vaccine (S19) and its association with MHC class I (BoLA-A) alleles (exons 2-3 and 4-5). Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was used for typing of BoLA-A exon 2-3 with DdeI and TaqI restriction enzymes; and exon 4-5 with HinfI in 45 crossbred calves. The PCR-RFLP analysis revealed five BoLA-A alleles each for exon 2-3 (A10/A19, A19, A18/19, A18 and A31) and exon 4-5 (A, B, C, D and E). Immune response against B. abortus S19 was assessed at the 4th week post vaccination; antibody response by standard tube agglutination test (STAT) and cell-mediated immunity by lymphocyte proliferation and lymphocyte-mediated cytotoxicity assays. Further, the macrophage function in terms of nitrite production was also analyzed. The association analysis of various BoLA-A alleles with the elicitation of immune response revealed that calves with certain defined genotypes induced significantly higher cell-mediated immune response in terms of lymphocyte proliferation with higher stimulation indices (S.I.) of 1.59 (BoLA-A19), 1.49 (A18/19) and 1.52 (HinfI-D); lymphocyte mediated cytotoxicity (55.52 % in A19) and nitrite production (43.40 μM in A31). It is assumed that allelic variants of BoLA-A (exons 2-3 and 4-5) were associated with the differential immune response of calves to B. abortus S19 vaccination. Therefore, further studies on association analysis of MHC class-I genes in large number of cattle may generate more information and might be useful for adapting the alternative approach of exploring genetic resistance in the cattle herd against bovine brucellosis.