Induction of macrophage growth by lipoprotein.

Cell-free tumorous ascitic fluid stimulated growth of variously induced mouse peritoneal macrophages and resident macrophages in vitro. This induction of macrophage growth by the tumorous ascitic fluid was confirmed by autoradiography. The macrophage growth-stimulating activity was stable on heating at 100 degrees C, in contrast to that of macrophage growth factor (colony stimulating factor) previously reported. This heat-stable macrophage growth-stimulating activity was recovered in the lipoprotein fraction of tumorous ascitic fluid. The lipoprotein from heat-treated normal mouse serum also induced growth of macrophages. These results indicate that lipoprotein can induce macrophage proliferation, at least in vitro.