DCs expressing Env and presenting antigen suppress CD4⁺ T-cell proliferation. DCs were infected with vaccinia virus encoding IIIB Env or control vaccinia encoding T7 polymerase and cocultured with CFSE-labeled PBMCs with 0.1 ng/mL TSST-1 and with or without sCD4. This concentration of superantigen requires presentation by DCs as no proliferation is observed in their absence. Proliferation of CD4⁺ T cells was measured 5 days later by flow cytometry. Quadrants are labeled with the percent of events in each. Experiments shown are representative of 3 independent experiments.