Levels of T cell activation were already significantly higher in SIVmac251-infected macaques at 7 days (p<0.001 for CD3+; p<0.001 for CD4+ and p<0.05 for CD8+ T cells) and 21 days post infection (p<0.01 for CD3+; p<0.05 for both CD4+ and CD8+ T cells) (Fig. 2). Here, CD4 is linked to infection.