Elevated levels of macrophage inflammatory protein 2 in severe murine peritonitis increase neutrophil recruitment and mortality

We hypothesized that chemokines may play important roles in a cecal ligation and puncture (CLP) model of septic peritonitis in CD-1 mice. Concentrations of C-X-C (macrophage inflammatory protein 2 [MIP-2] and ENA-78) and C-C (MIP-1alpha and JE) chemokines were measured (by enzyme-linked immunosorbent assay) in serum, peritoneal lavage fluid, lung, and liver at 4, 8, 24, 48, and 96 h after CLP. Significant elevations in all measured chemokines occurred in peritoneal fluid after CLP (P < 0.05). MIP-2, in particular, increased dramatically (>400-fold, P < 0.001) in peritoneal fluid, serum, and to a lesser extent lung and liver (P < 0.05). Increased MIP-2 was correlated with severity of sepsis (P < 0.001). To determine the significance of this finding, mice were passively immunized prior to CLP with polyclonal antibody to MIP-2, which decreased mortality from 85 to 38% at 96 h (P < 0.01). To further understand the mechanism of the effect of MIP-2, additional measurements demonstrated that anti-MIP-2 prior to CLP decreased the percent neutrophils in peritoneal fluid (55% +/- 12%, compared with 82% +/- 10% in controls), but no significant changes in tumor necrosis factor alpha, interleukin-6, or interleukin-10 occurred. MIP-2 contributes to the inflammatory response and overall mortality in this model of severe septic peritonitis, possibly by increasing recruitment of neutrophils, which clear bacteria but may also injure the host.