The ability of human FDCs to control T-cell proliferation in response to sAg. Varying numbers of FDCs (A through D) or B cells (A) were cultured with 1 × 105 autologous tonsil T cells and sAg (100 ng/mL) for 3 days (A and B) or allogeneic tonsil T cells and sAg (100 ng/mL) for 5 days (C and D). Tritiated thymidine uptake was measured during the last 24 hours of culture. Each bar represents the mean cpm + SEM of seven (A) or five (B through D) independent experiments. Cpm of cultures containing only T cells ranged from 193 to 1,290 in (A), 519 to 1,846 in (B), 138 to 2,547 in (C), and 541 to 2,158 in (D). Cpm of cultures containing only irradiated FDCs or B cells were always less than background (T cells alone). FDC significantly inhibited T-cell proliferation at a 1:5 and 1:20 ratio in (A) and (C), and at a 1:5 ratio in (B) and (D). B cells significantly augmented T-cell proliferation at a 1:5 and 1:20 ratio in (A). Statistical differences were determined using a pairedt-test.
