Depression of macrophage function by lipoprotein from tumorous ascites

Various tumorous ascites inhibited the antibody-dependent macrophage-mediated tumor lysis in vitro (ADMC) which had been found in a C3H/He mouse-MM46 tumor system. This inhibition of ADMC was due to functional depression of effector macrophages, evidenced by in vitro and in vivo pretreatment of effector cells with ascites lipoprotein. Ascites lipoprotein also had direct cytotoxicity against various cells, but in the ADMC system, two activities appeared separately; lower concentrations of lipoprotein caused inhibition of ADMC and higher one caused cytotoxicity to macrophages and tumor cells. The component of lipoprotein active in these two activities was the lipid moiety. These results suggest that lipoprotein in tumorous ascities depresses the function of macrophages resulting in the inhibition of ADMC and that lipid moiety is the essential component.