Lack of association of brucellosis resistance with (GT)13 microsatellite allele at 3′UTR of NRAMP1 gene in Indian zebu (Bos indicus) and crossbred (Bos indicus × Bos taurus) cattle

Natural resistance associated macrophage protein 1 (NRAMP1), an integral transmembrane protein, is reported to influence the intraphagosomal microbial replication and thereby confer resistance to several intracellular pathogens in mice. In bovine, a significant association of (GT)13 allelic variant of polymorphic microsatellite at 3′ untranslated region (UTR) of NRAMP1 gene with natural resistance to brucellosis has been established. The present study was aimed to detect polymorphism at 3′UTR of NRAMP1 gene in Hariana breed of Bos indicus cattle and Holstein Friesian crossbred (B. indicus × Bos taurus) cattle, and to determine the association of this polymorphism with resistance/susceptibility to brucellosis. The (GT)n polymorphism at 3′UTR in terms of variation in fragment length was determined using denaturing polyacrylamide gel analysis of radioisotope incorporated amplicon of 174 bp. Screening of a total of 100 samples (comprising 50 random samples of each breed) revealed that animals were of same genotype, i.e., homozygous (GT)13/(GT)13. Sequencing of amplicons from representative animals confirmed the presence of (GT)13 repeat. For association study, the animals that were positive in all three serological tests (viz., RBPT, STAT and ELISA) and had history of abortion were grouped as “affected”; whereas the animals that were negative in all these tests and completed third lactation without any history of abortion were grouped as “non-affected”. Since, all animals belonging to either group were homozygous (GT)13, association could not be established. However, the present study demonstrated that the presence of (GT)13 allele even in homozygous condition could not provide enough resistance to brucellosis in a naturally infected herd.