Local complement activation regulates T-cell Fas expression after antigen stimulation. (A) Flow cytometric plots of Fas expression on CFSE-labeled Mar T cells stimulated in vitro (3 days) with WT, Daf1^−/−, or C3^−/− macrophages plus HYDby peptide (MFI, isotype control-, anti-Fas-). Results are means of triplicate wells. Data are representative of 4 individual experiments. (B) Fas expression on Mar T cells in spleens (gated on Mar TCR Vβ6⁺ cells) of recipient male WT, Daf1^−/−, or C3^−/− mice 3 days after adoptive transfer (10 × 10⁶ cells/mouse). Results are depicted as means plus or minus SD of n = 3 or 4 per group. (C) Mean fluorescent intensities of anti-CD3/CD28–stimulated WT or C5aR^−/− T-cell surface Fas levels on addition of recombinant C5a after 72 hours. *P < .05 versus WT. Fas levels (MFI) on unstimulated WT was 25 and on C5aR^−/− T cells was 28 (not shown). (D) Flow plots of polyclonal H-2^b WT or C5aR^−/− CD4 T cells after injection into B6xBalb/c F1 WT or Daf1^−/− recipients (day 3) depicting surface Fas MFI. The experiment was repeated twice with similar results. *P < .05 versus WT.