Endothelial cells enhance the human pokeweed mitogen lymphocyte response

The effect of endothelial cells (EC) on lymphocyte mitogen responses was examined. Irradiated or mitomycin C treated EC were co-cultured with allogeneic peripheral blood mononuclear cells (PBM), and proliferative responses to pokeweed mitogen (PWM) and phytohemagglutinin (PHA) were assessed by 3H-thymidine incorporation. Compared to lymphocyte responses in the absence of EC, EC co-culture enhanced PWM responses at 72 hours by 55 +/- 28%, 103 +/- 24%, and 96 +/- 9% at EC:PBM ratios of 1:30, 1:10, and 1:3, respectively. The EC co-culture also resulted in significant lymphocyte responses to otherwise submitogenic doses of PWM (10(-4) micrograms/ml) as well as an accelerated kinetics of response. There was no effect of EC on PHA responses. The EC effect appeared not to require cell contact for its expression; however, supernates of EC cultures were not capable of reproducing the effect. On a cell-for-cell basis, EC were more potent in enhancing responses of adherent-cell-depleted lymphocytes than either allogeneic or syngeneic monocytes. Fibroblasts could not substitute for EC in enhancing PWM response, suggesting that the effect was not a nonspecific feeder phenomenon. The EC may play a role in modulating some immune responses in vivo, especially those occurring in areas of inflammation, neovascularization, and endothelial cell proliferation.