Changes in proliferating memory CD4⁺ T-cell subsets in neonatal tissues in pediatric SIV infection. (A) Very early, selective depletion of proliferating memory (BrdU⁺ CD95⁺) CD4⁺ T cells was consistently observed in the intestine of infected neonates by 3-7 days of infection. (B) After 21 days infection, massive loss of proliferating memory CD4⁺ T cells persists in all tissues examined. Flow cytometric plots indicate the distribution and frequency of proliferating (BrdU⁺, blue) cells in tissues having an activated (CD69⁺) and/or memory (CD95⁺) phenotype among all gated CD4⁺ T lymphocytes. Plots were gated through CD3⁺CD4⁺ lymphocytes. Data are expressed as means ± SE (*P < .05, **P < .01).