T-cell Bcl-2 and caspase-3 expression are regulated by locally produced C5a binding to T cell–expressed C5aR. (A) Expression of message for Bcl-2 in responding Mar T cells after stimulation with Dby-loaded WT, Daf1^−/−, C3^−/−, or Daf1/C3^−/− APCs (quantitative RT-PCR). Data are representative of 2 individual experiments. Error bars represent SD. (B) Flow cytometric analysis of intracellular Bcl-2 expression in unstimulated (left) or anti-CD3/CD28 stimulated (right) WT T cells plus recombinant C5a (50 ng/mL). Assays were performed at 72 hours. Data are representative replicates of 3 individual experiments. (C) Bcl-2 expression in anti-CD3/CD28-stimulated WT T cells plus or minus C5aR antagonist (C5aR-A, 0.1 μM, 72 hours) or vehicle control (left) and in anti-CD3/CD28–stimulated C5aR^−/− T cells (right, 48 hours). Data are representative replicates of at least 2 or 3 individual experiments per group. Numbers in each panel depict the mean fluorescence intensity. *P < .05. (D) Caspase-3 expression in anti-CD3/CD28–stimulated WT or C5aR^−/− T cells (120 hours). Analogous results were detected at 72 hours (2.1% caspase-3⁺ WT T cells vs 5.1% C5aR^−/− T cells, not shown). Data are representative replicates of 3 individual experiments.