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

天然抗性相关巨噬细胞蛋白1（NRAMP 1）基因最初被发现是控制小鼠对胞内病原体天然抗性的基因。Beg^s和Beg^r小鼠对鸟分枝杆菌（Mycobacterium avium，Mavium）感染易感性的差异在于位于1号染色体上的Nramp-1基因仅有一个碱基对突变点的差异，且抗性不仅在感染的早期阶段表达，而且在感染的后期阶段也表达。Nrarnp-1基因表达于分布于肝、脾和淋巴结的各种类型的巨噬细胞上。近年来，在人类和包括牛和猪在内的各种动物中发现了该基因的同源物。然而，目前尚不清楚这些动物的Nramp-1基因是否具有对分枝杆菌感染表现出抗性的能力。在这个时候，我们打算建立一个体外感染模型，通过使用猪肺泡巨噬细胞。鉴于我国猪非典型分枝杆菌病是一种常见病，本研究旨在探讨NRAMP 1基因与猪分枝杆菌感染易感性的关系。从健康猪的肺中单独收集肺泡巨噬细胞，并感染五株M. avium。在我们所调查的每头猪中，即使这些动物先前感染过M avium，细菌的体外增殖模式也几乎相同。用RT-PCR方法检测了感染猪巨噬细胞中NRAMP 1 mRNA的表达，并与正常对照组进行了比较，结果表明，感染猪巨噬细胞中NRAMP 1 mRNA的表达量与正常对照组相比有显著差异。将这些结果结合在一起，很可能所有具有接近的NRAMP 1基因型的个体都可能表现出相同的表型。

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.