PB CD4+ T-cell populations were resuspended at a density of 1 × 106 cells/ml in culture medium with 10% FCS, and 0.5 ml cell suspensions were dispensed into the wells of 24-well microtiter plates (Coster) coated with 1 μg/ml anti-CD3 mAb (Immunotech, Marseille, France). The cells were incubated with 1 μg/ml anti-CD28 mAb (Immunotech) in the presence or absence of the indicated concentrations of IL-10 (Becton Dickinson, San Jose, CA, USA) at 37°C in a humidified atmosphere containing 5% CO2 [28]. Culture supernatants were collected 36 hours later and cell-free samples were stored at -30°C until cytokine assay.