CD4 and infection: Before the start of treatment, animal 30577 had a viral set-point of ~106 viral RNA copies per ml plasma, and had the expected changes associated with a virulent infection, namely gradual decreases in percentages CD4+ T lymphocyte counts (< 15%; Fig. 3), absolute CD4+ T lymphocyte counts (< 500 per μl), and CD4+/CD8+ T lymphocyte ratios (ratio < 1 from week 8 to week 20).