Figure 3.

Characterization of suppression by T_reg cells after CD28-SA-mediated expansion. (a) After a 12 day culturing period using CD28-SA plus IL-2 T_reg cells (open circles; 800-fold expansion) and freshly isolated T_reg cells (filled circles) were cocultured with freshly isolated CD4⁺ CD25^– T_ind cells at the given T_reg to T_ind cell ratios. Filled diamond: Proliferation of T_ind cells in the absence of T_reg cells. Detached circles: Proliferation of T_reg cells without T_ind cells. Cultures were stimulated for 3 days with Con A and proliferation was measured by [³H]thymidine incorporation. (b) CD28-SA-expanded T_reg cells (53 days in culture; 5.3 × 10⁸-fold expansion) were cultured with nylon wool non-adherent indicator T cells (T_ind) of which half had direct cell-contact and the other half was separated from the T_reg cells by a millicell® cell-culture insert.