Activation of tumoricidal properties in macrophages by lipopolysaccharide requires protein-tyrosine kinase activity

The purpose of these studies was to determine whether triggering murine peritoneal macrophages to a tumoricidal state by lipopolysaccharide (LPS) requires protein-tyrosine phosphorylation. The LPS-triggered activation of mouse macrophages to lyse syngeneic B16 melanoma cells was significantly inhibited in a dose-dependent manner by the protein-tyrosine kinase (PTK) inhibitors genistein, herbimycin A, and tyrphostin. Genistein was effective only when added to macrophages prior to or simultaneously with LPS. Genistein potently inhibited the productive interaction of macrophages with LPS but had only a minor effect on the action of interferon-gamma. The effects of genistein on LPS-triggered macrophage activation were not due to nonspecific changes in macrophage metabolism or toxicity because genistein did not prevent lysis of tumor cells by activated macrophages, nor did it reduce the capacity of macrophages to phagocytose antibody-opsonized sheep erythrocytes. Western blot analysis with antiphosphotyrosine monoclonal antibody revealed that incubation of macrophages with LPS produced a rapid increase in tyrosine phosphorylation of several proteins and that the induced phosphorylation could be inhibited by effective concentrations of genistein, herbimycin A, or tyrphostin. Taken together, these data indicate that protein-tyrosine phosphorylation plays an important role in LPS-induced tumoricidal activation of macrophages.