Treg suppression of HIV infection is dose dependent. Tcons were infected with HIV and cocultured at Tcon:Treg ratios of 1:0, 1:0.1, and 1:1. Levels of HIV p24^Gag measured by ELISA in culture supernatants 3 days after infection. One representative experiment for the X4 strain (left panel) and the R5 strain (right panel) of HIV are shown (n = 2 for each virus).