Monocyte-induced proliferation in ECs is dose dependent and EC density dependent. (A) 3H-thymidine incorporation (disintegrations per minute [DPM]) is dependent on the relative ratio of monocyte to EC density. (B) Monocytes added in proportional numbers to ECs, seeded in increasing densities, exhibit a decreasing mitogenic effect as ECs approach confluence (n ≥ 3).