Inheritance of the Ity' or the ItyS allele of the Ity murine gene confers resistance or increased susceptibility, respectively, to SalmoneUla typhimurium infection. Recent studies have documented that Ity gene expression may determine net intracellular replication of S. typhimurium by modulating macrophage function. The purpose of this study was to determine if Ity gene expression modulated macrophage stem cell proliferation as well. To detect possible Ity-associated alterations in macrophage

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... em cell proliferation during endotoxin challenge or S. typhimurium infection, the congenic strain pair BALB/c (ItS) and C.D2-Idh-1, Pep-3 N20F8 (Ityr) were injected intraperitoneally with 25 ,ug of bacterial lipopolysaccharide (LPS) or -103 S. typhimurium, and myelopoiesis was evaluated. At 72 h after LPS injection, both BALB/c and C.D2 mice developed comparable degrees of bone marrow hypocellularity and splenomegaly, and cell sizing profiles indicated a normal response to a single injection of LPS in both strains of mice. Although an inhibitor to colony-stimulating factor activity was detected in the sera and plasma of C.D2 mice, the number of myeloid stem cells cultured from the bone marrow and spleen of each mouse strain were comparable. S. typhimurium infection resulted in earlier symptoms, a larger bacterial load, a higher mortality rate, and a greater bone marrow hypocellularity and splenomegaly in BALB/c mice compared with those in C.D2 mice. Despite a dramatic increase in bacterial load, a decrease in both bone marrow and splenic myeloid stem cell numbers was noted in BALB/c mice, while stem cell numbers remained constant in C.D2 mice between days 3 and 5 and increased dramatically at day 7 after infection. These data suggest that BALB/c and C.D2 mice may exhibit a divergent myelopoietic response to S. typhimurium infection. It appears that a paradoxical failure of myelopoiesis in ItyS mice during S. typhimurium infection may contribute to the observed increase in mortality. 1375 on May 8, 2020 by guest http://iai.asm.org/ Downloaded from 1376 PETERSON ET AL. INFECT. IMMUN. on May 8, 2020 by guest http://iai.asm.org/ Downloaded from