Macrophage-mediated natural cytotoxicity against various target cells in vitro. II. Macrophages from rats of different ages.

Adherent, predominantly phagocytic mononuclear cells from various rat tissues express spontaneous cytoxicity against diverse target cells in vitro. The extent to which cytotoxicity was expressed by effector cells depended on the age of donors. Cytolytic effector-cell capacity was already fully developed a few days after birth, and persisted over many months, but was clearly reduced in senescence. Similarly, the ability to intensify natural cytotoxicity by peptone in vivo was already fully manifested in the newborn, but was significantly diminished in old rats.