Pentacyclic oxindole alkaloids from Uncaria tomentosa induce human endothelial cells to release a lymphocyte-proliferation-regulating factor

In the present study we show that pentacyclic but not tetracyclic oxindole alkaloids from Uncaria tomentosa (Willd.) DC. (Rubiaceae) induced EA.hy926 endothelial cells to release some yet to be determined factor(s) into the s upernatant; this factor was shown to significantly enhance proliferation of normal human resting or weakly activated B and T lymphocytes. In contrast, proliferation of normal human lymphoblasts and of both the human lymphobla stoid B cell line Raji and the human lymphoblastoid T cell line Jurkat was inhibited significantly while cell viability was not affected. Tetracyclic oxindole alkaloids dose-dependently reduce the activity of pentacyclic oxin dole alkaloids on human endothelial cells.