CCL2 and peritonitis: Removal of either macrophages or mast cells resulted in attenuation of neutrophil infiltration into the peritoneal cavity of WT mice without affecting the levels of MCP-1 and KC in response to intraperitoneal administration of LPS; however, depletion of resident mast cells inhibited neutrophil accumulation as well as MCP-1 and KC production in response to zymosan, suggesting that mast cells may be the primary source of MCP-1 in peritonitis caused by certain stimuli, such as zymosan.