Method of T cell stimulation determines HIV-1 susceptibility. (A) Comparison of viral replication in TN, TCM and TEM cells that were stimulated by DC or by CD3/CD28 crosslinking with antibodies. The T cells were stimulated for 4 days, harvested and re-plated before infection with X4 HIV-1. Viral spread was followed by CA-p24 ELISA, of which the results of day 6 are shown. (B) To measure T cell proliferation TN, TCM or TEM cells were incubated with DC or α-CD3/CD28 antibodies and after 4 days, cellular proliferation was determined by 3H-thymidine incorporation. Error bars represent standard deviations. * p < 0.05 ; ** p < 0.01; *** p < 0.001.