LIPOPOLYSACCHARIDE AND SPLENIC TUMORICIDAL MACROPHAGE ACTIVATION

Splenic macrophage tumoricidal activity was examined and a splenic mac rophage tumoricidal assay was established. Initially, mixtures of lipo polysaccharide (LPS) and spleen single cell suspensions (SSCS) were cu ltured for 1-4 days. Adherent macrophages, washed free of nonadherent cells and LPS, were then examined and were found to lack tumoricidal a ctivity in a standard 18-h Cr-51 release assay. However, tumoricidal a ctivity was generated if LPS was added to the SSCS cultures at later t ime points during the L-day incubation period; maximal activity was se en when LPS was added on day 3. In parallel, significant changes in ma crophage autofluorescence and morphology, but not phenotype, were obse rved. Next, SSCS were cultured for 1-4 days without stimulating agents . Adherent macrophages were then washed free of nonadherent cells and LPS was added. Significant tumoricidal activity developed in time- and LPS concentration-dependent fashions. The presence of nonadherent spl een cells in physical contact with the macrophages during the SSCS cul ture was essential for the macrophages in the resultant monolayer to b e responsive to LPS. Activated splenic macrophage-mediated lysis of tu mor cells was shown to depend on the contact between the two cells.