Comparison of various assays to quantitate macrophage activation by biological response modifiers

Macrophages treated with various compounds that enhance host antitumor resistance exhibit measurable changes in metabolism, function, and surface antigens. In this study, murine peptone-induced peritoneal macrophages were stimulated in vitro by bacterial lipopolysaccharide (LPS), muramyl dipeptide (MDP), and poly I.poly C. They were subsequently compared in their ability to release superoxide and act as tumoristatic and tumoricidal effector cells. Superoxide generation was assayed by the reduction of ferricytochrome C. All three compounds failed to induce significant O2- release, unless the cells were also treated with phorbol myristate acetate (PMA). MDP was most active in potentiating the PMA response. In the tumor growth inhibition assay, cytostatic activity was comparable for all three compounds and did not exceed 32 percent. The combination of subthreshold levels of these compounds and hybridoma-derived MAF acted synergistically to induce potent cytostatic activity. In the chromium release assay, LPS and poly I.poly C rendered macrophages cytolytic for P815 target cells at concentrations greater than or equal to 1 microgram/ml. In contrast, significant cytolysis was observed with MDP only at 100 micrograms/ml. Defining precisely the effect of various biological response modifiers on several parameters of macrophage function may facilitate use of these agents in cancer therapy.