Natural resistance to infection with intracellular pathogens: cross-talk between Nramp1 and Lps genes

This study was designed to analyze the association of Nramp1 and/or Lps genes with differential protein expression in macrophages in order to select candidate proteins that might be related to resistance/susceptibility to various microbial infections under the control of the Nramp1 and/or Lps genes. The macrophage cell lines derived from bone marrow of Nramp1 or Lps congenic mice were utilized and high-resolution two-dimensional electrophoreis (2-DE), separating proteins according to their charge and size, was used as a window into alterations in gene expression and a means to compare the macrophages carrying a resistant allele of Nramp1 gene and/or normal allele of Lps gene, with their counterparts carrying either a susceptible allele of Nramp1 or defective allele of the Lps gene. We demonstrate that the changes of constitutive levels of two proteins named according to their isoelectric point/molecular weight (pI/Mr), p6.6/25 and p7.0/22, discriminate satisfactorily not only the macrophages congenic at the Nramp1 gene but also the macrophages congenic at the Lps gene, thus reflecting their common genotype (Nramp1r, Lps[n]). Furthermore, the decreased constitutive levels of these proteins in macrophages carrying a defective allele of Lps but preserving a resistant allele of Nramp1 can be, at least in part, restored by stimulation with interferon gamma or lipopolysaccharide. 2-DE immunoblot analysis identified the p7.0/22 protein as manganese superoxide dismutase. Bcl-2 appears to be the best candidate for p6.6/25 as suggested by 2-DE quantitative alterations and Western blot analysis. These proteins are important in the regulation of intracellular redox balance and the regulation of apoptosis in macrophages and their alterations might reflect closely the transport functions of ions or other charged substrates suggested for Nramp1 protein.