Induction of macrophage growth by effete cells.

When mouse peritoneal cells in early phase-inflammatory exudates were cultured in vitro, the number of polymorphonuclear leukocytes (PMNs) rapidly decreased, whereas the number of macrophages gradually increased during culture. Macrophage growth was also induced by addition of effete PMNs or their debris to macrophage monolayers. This phenomenon was not restricted to senescent PMNs, because effete spleen cells or effete tumor cells also induced macrophage growth. The activity of these cell debris was stable on heating at 100 degrees C and was partially recovered in the lipid fraction. These data suggest that tissue macrophages may proliferate when they scavenge effete PMNs or other host cells and that these cell debris may be important mediators in inducing growth of peripheral macrophages in inflammation and tumors or the normal steady state.