Central memory lymphocytes are preserved in blood after anti-FasL treatment. (A) Central memory (CM), effector memory (EM), and naive lymphocyte populations were defined on the basis of CD95 and CD28 expression. Significantly higher percentages (B) as well as absolute numbers (C) of CD95⁺CD28⁺ CM CD4 lymphocytes were observed at various time points after SIV infection in anti-FasL–treated animals. (D) The anti-FasL–treated animals had significantly higher percentages of CM CD8 lymphocytes at most time points after SIV infection. The percentages of naive (CD95⁻CD28⁺) CD8 lymphocytes were significantly lower at these times. *P < .05 (significant differences by paired testing). Error bars indicate SEM.