Examination of total CD4⁺ and CD8⁺ T cells and percentages of proliferating T-cell subsets from various tissues of neonates 10-14 days after SIV infection. (A) Bar charts demonstrating marked depletion of intestinal CD4⁺ T cells occurs by 10-14 dpi, accompanied by significant increases in intestinal CD8⁺ T cells, yet minimal changes are detected in CD4⁺/CD8⁺ T cells in the blood, lymph node or spleen in early SIV infection. Bars represent percentage of CD3⁺ gated lymphocytes expressing CD4 or CD8. Data are expressed as mean ± SEM (B) Representative flow cytometry confirms marked and selective depletion of proliferating (BrdU⁺) CD4⁺ T cells (left panels) concurrent with marked increase in CD8⁺ T-cell proliferation in early SIV infection (right panels). All plots were generated by gating through CD3⁺ lymphocytes and then CD4⁺ or CD8⁺ T cells. Data in panel B are from representative plots from a SIV-infected neonate 12 dpi and an age-matched (12-day-old) uninfected control.