Abstract
The lysosomal membrane transporter, Nramp1, plays a key role in innate immunity and resistance to infection with intracellular pathogens such as non-typhoidal Salmonella (NTS). NTS-susceptible C57BL/6 (B6) mice, which express the mutant Nramp1D169 allele, are unable to control acute infection with Salmonella enterica serovar Typhimurium following intraperitoneal or oral inoculation. Introducing functional Nramp1G169 into the B6 host background, either by constructing a congenic strain carrying Nramp1G169 from resistant A/J mice (Nramp-Cg) or overexpressing Nramp1G169 from a transgene (Nramp-Tg), conferred equivalent protection against acute Salmonella infection. In contrast, the contributions of Nramp1 for controlling chronic infection are more complex, involving temporal and anatomical differences in Nramp1-dependent host responses. Nramp-Cg, Nramp-Tg and NTS-resistant 129×1/SvJ mice survived oral Salmonella infection equally well for the first 2-3 weeks, providing evidence that Nramp1 contributes to the initial control of NTS bacteremia preceding establishment of chronic Salmonella infection. By day 30, increased host Nramp1 expression (Tg>Cg) provided greater protection as indicated by decreased splenic bacterial colonization (Tg