Effect of addition of (A) anti-CD95 Fab′ IgG alone or (B) followed by 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 three to four separate experiments in duplicate.