CD4 and infection: Consistent with the changes in number, CD4+ Tem cells were the most activated among the three CD4+ T cell subtypes, with significant increases on days 3 (7.70 ± 3.77, P = 0.0041), 4 (15.32 ± 11.31, P = 0.0209), and 7 (6.36 ± 3.86, P = 0.0111) compared to baseline (day 0, 1.77 ± 0.97), while HLA-DR+CD4+ Tcm cells only increased slightly and CD4+ naive T cells exhibited no change during infection (Figure 3C).