Changes in proliferating CD4⁺ and CD8⁺ T cells in neonatal tissues in SIV infection. Bars reflect percentages of each subset labeled with BrdU in respective tissues of SIV-infected (black bars) and uninfected age-matched normal neonates (white bars) at various stages of acute infection or age. Note by 12-14 dpi, there is marked depletion of proliferating CD4⁺ T cells (left) corresponding with a significant increase in proliferating CD8⁺ T cells (right). Data represent mean percentages of BrdU⁺ cells gated through either CD4⁺ or CD8⁺ T cells in each group ± SEM).