Macrophage-mediated natrual cytotoxicity against various target cells in vitro. I. Macrophages from diverse anatomical sites and different strains of rats and mice.

Adherent, predominantly phagocytic, mononuclear cells expressing spontaneous cytotoxic activity against diverse target cells in vitro were present in various tissues of different strains of rats and mice. Cells with such natural killer capacity were thus everywhere readily available for mobilization and activation. The inherent spontaneous killer capacity of adherent mononuclear phagocytes can be abrogated by silica particles in vitro, and can be considerably enhanced by appropriate stimuli in vivo. Spontaneous cytolysis mediated by unstimulated mononuclear phagocytes was consistently manifested only after a lag phase of 12-20 h and was quite nonspecific; there was no cogent correlation between susceptibility to lysis and transformation.