Granulocyte-macrophage-colony-stimulating factor-dependent peritoneal macrophage responses determine survival in experimentally induced peritonitis and sepsis in mice

Granulocyte-macrophage colony-stimulating factor (GM-CSF) plays a critical role in innate immunity by stimulating the differentiation of tissue macrophages via the transcription factor PU.1. Previous studies showed that GM-CSF deficient (GM-CSF^-/-) mice had susceptibility to and impaired clearance of group B streptococcal bacteria by macrophages. For these studies, we hypothesized that GM-CSF^-/- mice have increased susceptibility to peritonitis caused by immune dysfunction of peritoneal macrophages. We examined the role of peritoneal macrophages in pathogen clearance, cytokine responses, and survival in a murine cecal ligation and puncture (CLP) model of peritonitis/sepsis. Surprisingly, CLP minimally affected survival in GM-CSF ^-/- mice while markedly reducing survival in wild-type mice. This was not explained by differences in the composition of microbial flora, rates of bacterial peritonitis, or sepsis, all of which were similar in GM-CSF ^-/- and wild-type mice. However, survival correlated with peritoneal and serum TNF-α and IL-6 levels that were significantly lower in GM-CSF^-/- than in control mice. After peritoneal LPS instillation, GM-CSF^-/- mice also had improved survival and reduced TNF-α and IL-6 responses. In vitro studies demonstrated reduced secretion of TNF-α and IL-6 by peritoneal macrophages isolated from sham GM-CSF mice as compared with macrophages from sham control mice. Peritoneal instillation of GM-CSF ^-/- /PU.1⁺ macrophages, but not GM-CSF^-/-/PU.1 macrophages into GM-CSF^-/- mice conferred susceptibility to death after CLP or peritoneal LPS exposure. These results demonstrate that GM-CSF -/PU.1-dependent peritoneal macrophage responses are a critical determinant of survival after experimentally induced peritonitis/sepsis or exposure to LPS and have implications for therapies to treat such infections.