Phagocytosis and solubilization of fixed cells by metastatic hamster embryo fibroblasts, Nil2C2.

When Nil2C2, a metastatic clone derived from hamster embryo fibroblasts (Nil), was inoculated over [3H]leucine-labeled fixed cells, Nil2C2 cells solubilized and phagocytosed fixed cells, and the radioactivity was released into the culture medium as trichloroacetic acid-soluble fragments. The solubilization of fixed cells was dependent on both the time of incubation of living cells with fixed cells and the number of living cells inoculated. Nil2C2 cells were shown by autoradiographic and electron microscopic studies to peel off fixed cells and ingest them as large fragments. The solubilization of fixed cells was significantly decreased when plasminogen was depleted from the culture medium. Protease inhibitors such as leupeptin, epsilon-aminocaproic acid, and soybean trypsin inhibitor partially inhibited the proteolysis and phagocytosis of Nil2C2 cells. Mouse peritoneal macrophages activated by Salmonella typhimurium solubilized fixed cells after the addition of 12-O-tetradecanoylphorbol-13-acetate. However, they did not phagocytose fixed cells as large fragments.