The effect of Fas cross-linking on proliferation of T cells isolated from HIV-infected or noninfected individuals. We analyzed the ability of anti-Fas antibodies to modulate T-cell proliferation in the presence of solid-phase bound anti-CD3 antibodies used at different doses. Proliferation of freshly isolated T cells was measured in response to 1 μg/mL or 10 μg/mL anti-CD3 in the presence or absence of Fas triggering. Thymidine incorporation was measured after 3 days of activation. Error bars represent standard deviation measured in triplicate samples, 1 representative experiment of 3 is shown. (A) To compare the proliferative effect of Fas cross-linking on T cells of HIV-infected and noninfected individuals, we activated CFSE-labeled T cells using 1 μg/mL coated anti-CD3 mAb in the presence or absence of Fas cross-linking for 4 days. The percentage of proliferating T cells was calculated as shown by a typical sample, where the filled histogram represents T cells activated in the presence of anti-Fas, and open histogram represents T cells activated in the presence of control IgM antibodies. (B) T cells isolated from a cohort of HIV-infected (closed symbols) or noninfected (open symbols) individuals were activated using 1 μg/mL anti-CD3 mAb, and 1 μg/mL (C) or 0.25 μg/m (D) anti-Fas or isotype control mAbs. Proliferation was analyzed in CD4⁺ and CD8⁺ T cells by flow cytometry; percentages of proliferating cells are shown.