Effects of cimetidine on in vitro transformation of peripheral monocytes to macrophages in healthy volunteers and cancer patients

Abstract Monocyte-to-macrophage transformation is a phenomenon which correlates with the absolute number of mononuclear cells, principally lymphocytes, contained in the culture. The addition of cimetidine to cultures of mononuclear cells from the peripheral blood of healthy volunteers enhances monocyte transformation (probably by way of blocking the H2 receptors of suppressors T lymphocytes) regardless of the absolute number of monocytes in the culture or of basal transformation rates. Removal of the lymphocytes from the cultures lowers the basal transformation rate and prevents the effect of cimetidine. The addition of histamine to the cultures causes significant depression of the monocyte transformation rate; this effect is partly offset by the concurrent addition of cimetidine. In the case of cancer patients, mononuclear cell cultures from peripheral blood fail to respond to cimetidine even though basal transformation rates are not significantly different from those of healthy controls; this suggests some intrinsic impairment of monocyte function, possibly mediated by blocking factors produced by the tumor.