Association of microsatellite (GT)n polymorphism at 3′UTR of NRAMP1 with the macrophage function following challenge with Brucella LPS in buffalo (Bubalus bubalis)

Brucella abortus is a facultative intracellular pathogen that survives and replicates in host macrophages. Hence, macrophage function plays an important role in influencing natural resistance/susceptibility to intracellular pathogen. The natural resistance associated macrophage protein 1 (NRAMP1; erstwhile referred as Ity/Lsh/Bcg), a transmembrane protein, regulates activity of macrophages against intracellular pathogens. In bovine, natural resistance to brucellosis is significantly associated with (GT)13 allelic variant of microsatellite locus at 3′ untranslated region (3′UTR) of the NRAMP1 gene. In the present study we screened 65 Murrah breed of buffalo (Bubalus bubalis) to identify polymorphism at 3′UTR of NRAMP1 gene and evaluate the association of these polymorphisms with the macrophage function. Four allelic variants (viz., GT13, GT14, GT15 and GT16) were identified. Majority of the buffaloes were of either homozygous (GT)14/(GT)14 or heterozygous (GT)14/(GT)15 with (GT)14 allele occurring most frequently (62%). For association study, non-vaccinated and serologically negative animals were divided into three genotypic groups: group 1 (n = 2) comprising animals of homozygous (GT)13 genotype, whereas, group 2 (n = 4) and group 3 (n = 6) consisted animals of heterozygous [(GT)13/(GT)n, where n ≠ 13] and non-(GT)13 [(GT)n/(GT)n, where n ≠ 13] genotype, respectively. Macrophages, after maturation, were challenged with Brucella LPS to assay the macrophage function in terms of H2O2 and NO production. The (GT)13 allele, either in homozygoous {(GT)13/(GT)13} or heterozygous {(GT)13/(GT)n, where n = 14, 15 or 16}, was significantly (p < 0.01) associated with increased production of H2O2 and NO. In this manuscript, for the first time, we have identified (GT)13 allelic variant and demonstrated its significant association with the improved macrophage function in buffalo.