Finally, to directly link MMP12 catalytic activity with the controlled normal succession of IFN-γ-classically activated macrophage populations to alternately activated macrophages in vivo, we injected Mmp12+/+ B10.RIII mice with 5 mg/kg MMP12-specific inhibitor (Rxp470.1) (n = 4) or vehicle (n = 4) daily for 4 days during the development of peritonitis. This evidence concerns the gene MMP12 and peritonitis.