C3-mediated phagocytosis induced in murine Kupffer cells by "in vitro" activation with endotoxin

Binding and phagocytosis of red blood cells by Kupffer cells, mediated by C3 receptors, have been studied by incubating sheep red blood cells opsonized with C3, and Kupffer cells isolated from rat and mouse livers. Sheep red blood cell-binding was followed by internalization and phagocytosis only after preincubation of Kupffer cells with bacterial endotoxin. In both species of cells there was a direct relationship between the value of the phagocytic index and the amount of endotoxin needed to stimulate the cells. Increased phagocytosis was related to an increase in the number of phagocytosing cells; it did not depend on an increase in the number of red blood cells internalized per Kupffer cell. C3-mediated phagocytosis, together with the intrinsic and extrinsic antiviral activities, and the synthesis of interferon which take place in activated cells may play an important role in non-specific immunity.