Functional analysis of natural resistance associated macrophage protein-1(NRAMP1) encoded by Bcg gene

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Natural resistance associated macrophage protein-1 (NRAMP1) gene was initially found as the gene that controls the natural resistance to intracellular pathogens in mice. The difference in susceptibility to Mycobacterium avium (Mavium) infection between Beg^s and Beg^r mice lies on the difference in the mutation point of only one base pair of the Nramp-1 gene which is located on chromosome 1 and the resistance is expressed not only in the early stages but also in the latter period of infection. The message of Nrarnp-1 gene is ex-pressed on various types ofmacrophages which distributes to the liver, spleen and lymph nodes. In recent years the homologue of this gene has been found in humans and various kinds of animals including cows and pigs. However, it is not clear whether the Nramp-1 gene of these animals has the ability to exhibit the resistance to mycobacterium infection or not. At this time we contemplate to establish an in vitro infection model by using swine alveolar macrophages. This study is designed to examine the relationship between NRAMP1 gene and susceptibility to M avium infection because atypical mycobacteriosis in swine is a common disease in our country. Alveolar macrophages were collected from the lungs of healthy swine individually and infected with five strains of M.avium. The in vitro proliferation patterns of the bacteria in every swine which we investigated were almost the same even though these animals had been priorly infected with M avium. The expression of NRAMP1 mRNA in the macrophages from infected swine was also compared with those of normal healthy controls by RT-PCR and significant differences in the amount of PCR products were noted in some infected individuals. Taking these results together, it is probable that all individuals having a close NRAMP1 genotype may exhibit the same phenotypes.