CCR5-expressing CD4 lymphocytes were higher in treated compared with control macaques at early times after SIV infection. (A) A significantly higher percentage of CCR5⁺CD4⁺ lymphocytes was observed in the anti-FasL–treated group at 2 and 4 weeks after SIV infection. In this group, CCR5⁺CD4⁺ T cells were nearly twice the baseline values from 2 to 4 weeks after infection (an effect not seen in the control group). (B) The CD95⁺CCR5⁺ subset of CD4 lymphocytes was compared at 2 and 4 weeks to study the effect of infection on the memory CCR5⁺CD4⁺ subset. Representative dot plots from anti-FasL (Bi) and IgG (Bii) animals showed a decline in this subset for control animals. (C) The average values from the groups show the memory population declined in control animals but not in the anti-FasL–treated group. Error bars (panels A and C) indicate SEM. Asterisks indicate significant differences (P <.05).