(A) Effect of addition of anti-CD95 IgM on the percentage of apoptosis in untreated or FK-treated Nef transfectants cultured in RPMI + 0.1% FCS for up to 24 hours. Apoptosis was quantified by PI staining and flow cytometry at different culture times after serum starvation. Data are the mean ± SD of four separate experiments in duplicate. (B) Surface expression of CD95 in untreated or FK-treated Nef transfectants cultured in RPMI 0.1% FCS for 24 hours. Unshadowed histograms represent cells treated with anti-CD95 + GAM-FITC, and shadowed histograms are negative controls (cells treated with anti-p66 of HCMV + GAM-FITC). X-axis, relative CD95 expression detected by fluorescence intensity (log scale); y-axis, relative number of cells. A representative of four separate experiments is shown. The MFI of the four experiments (AU) was 189 ± 28 (JH6.2), 277 ± 51 (JBru.2), 325 ± 64 (JBru.2 + FK), and 394 ± 76 (JBru.3).