WEB 2170 diminished the proliferation of B lymphocytes. Tonsillar B lymphocytes were cultured with isolated follicular dendritic cells for 120 hours with and without WEB 2170 (10-8 M). After 114 to 116 hours, [3H]-thymidine (1.0 μCU per well) was added, and the cells were harvested 4 to 6 hours later. The histograms represent cell proliferation as expressed by incorporation of [3H]-thymidine. Upper panel shows assessment of mixed tonsillar B lymphocytes (n = 4); lower panel shows assessment of low-density tonsillar B lymphocytes The gray and black bars represent two separate experiments performed in triplicate (n = 2).