Phenotypic and functional analysis of murine resident and induced peritoneal macrophages

Primary macrophages from the peritoneal cavities of mice are commonly used ex vivo to produce inflammatory cytokines and test anti-inflammatory agents. Although approximately 1 million peritoneal macrophages can be obtained from an untreated mouse, more than twice that number can be collected 48 to 72 h after intraperitoneal injection of sterile inducing agents such as Brewer thioglycollate broth, casein, and proteose peptone. However, whether 'induced' macrophages are functionally equivalent to 'resident' peritoneal macrophages has been unclear. Flow cytometric analysis revealed significant phenotypic differences between these 2 macrophage types. Resident and induced peritoneal macrophages also demonstrated markedly different capacities to produce the inflammatory cytokines interleukins 6 and 1beta in response to lipopolysaccharide stimulation in vitro. Increased understanding of the differences between resident and induced peritoneal macrophages likely will help investigators decide which macrophage type is appropriate for their in vitro assay needs.