Objectives: In vivo lipopolysaccharide (LPS) tolerance on bacterial infection was investigated, focusing on liver macrophages.
Methods: LPS tolerance was induced by intraperitoneal injections with 5 μg/kg of LPS for 3 consecutive days, and then mice were intravenously infected with Escherichia coli.
Results: All LPS-primed mice survived lethal bacterial infection. Drastic enhancement of bactericidal activity of liver macrophages strongly contributed to bacterial clearance. Although LPS-primed mice produced substantial amounts of tumor necrosis factor (TNF) inside the liver, TNF efflux into the systemic circulation was markedly suppressed. These mice showed a dramatic increase in CD11b+ monocyte- derived macrophages in the liver. The CD11b+ macrophages that increased in LPS-primed mice were those with strong phagocytic/bactericidal activity and an upregulated expression of Fcγ receptor I, but the subfraction with a potent TNF-producing capacity and poor phagocytic activity diminished. The adoptive transfer of CD11b+ macrophages from LPS-primed mice to control mice increased survival after bacterial infection and reduced the elevation of plasma TNF. LPS priming did not affect the CD68+ resident Kupffer cells, and CD68+ Kupffer cell-depleted mice still exhibited LPS tolerance with strong resistance to bacteremia.
Conclusions: LPS tolerance recruits CD11b+ macrophages to the liver with enhanced bactericidal activity, which plays a central role in resistance to lethal bacteremia.
Keywords: Bacterial septicemia; CD11b+; Escherichia coli infection; Lipopolysaccharide tolerance; Monocyte-derived macrophages; Tumor necrosis factor.
© 2017 S. Karger AG, Basel.