Effects of peripheral blood monocytes on human vascular cell proliferation

Incubated human peripheral blood monocytes release a factor(s) which specifically stimulates homologous vascular smooth muscle (SMC) but not endothelial cells (EC) to proliferate in vitro. Conditioned medium from activated monocytes significantly (P less than 0.001) stimulated proliferation of SMC within 6 days of culture while media from non-activated monocytes was less effective (P less than 0.01). Non-vascular smooth muscle cells (human myometrium) were less responsive to such media (P less than 0.01 and P less than 0.05, respectively). These findings suggest that blood monocytes may play a key and until now unsuspected role in arterial smooth muscle proliferation, a recognized event in the initial stages of atherogenesis.