At 21 days of infection, the level of proliferating CD3+T cells, CD4+T cells and CD8+T cells in SIVmac251 infected macaques were all significantly higher than those infected with SHIV162p3 (from 16.56% to 56.1%, 5.096% to 37%, 31.12% to 66.58% (p<0.001; p<0.05 and p<0.01 respectively), However T-cell proliferation decreased thereafter, and by day 28, values were indistinguishable between cohorts. This evidence concerns the gene CD4 and infection.