Malaria parasite-mediated alteration of macrophage function and increased iron availability predispose to disseminated non-typhoidal Salmonella infection.

Disseminated infections with non-typhoidal Salmonella (NTS) are a significant cause of child mortality in sub-Saharan Africa. NTS infection in children is clinically associated with malaria, suggesting that malaria compromises control of disseminated NTS infection. To study the mechanistic basis for increased NTS susceptibility, we utilized a model of concurrent infection with Salmonella enterica serotype Typhimurium and Plasmodium yoelii Underlying malaria blunted monocyte expression of Ly6C, a marker for inflammatory activation, and impaired recruitment of inflammatory cells to the liver. Hepatic mononuclear phagocytes expressed lower levels of iNOS, TNFα and GM-CSF and increased production of IL-10 and heme oxygenase-1, indicating that that underlying malaria modifies the activation state and inflammatory response of mononuclear phagocytes to NTS. P. yoelii infection also increased intracellular iron levels in liver mononuclear cells, as evidenced by elevated levels of ferritin and by rescue of a S. Typhimurium tonBfeoB mutant defective for iron uptake. In addition, concurrent P. yoelii infection partially rescued the systemic colonization defect of a S Typhimurium spiB mutant defective for type III secretion system-2 (T3SS-2), indicating that the ability of phagocytic cells to limit spread of S. Typhimurium is impaired during concurrent P. yoelii infection. These results show that concurrent malaria increases susceptibility to disseminated NTS infection by blunting macrophage bactericidal mechanisms and providing an essential nutrient that enhances bacterial growth.