GRANULOCYTE-MACROPHAGE-COLONY-STIMULATING FACTOR-DEPENDENT PERITONEAL MACROPHAGE RESPONSES DETERMINE SURVIVAL IN EXPERIMENTALLY INDUCED PERITONITIS AND SEPSIS IN MICE

Abstract

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.