Activated B cells with inhibitory properties can be found in human tonsils. (A) Representative example for phenotype of purified tonsillar B cells according to CD38 and IgD expression. Upper quadrant separates CD38⁺ from CD38⁺⁺ B cells. Large cells gated on R5; small cells gated on R4; PI⁺ B cells (R2) gated out. (B) Sort gates for separation of IgD⁺ CD38⁺⁺ B cells (R6 and R1 and not R2) and IgD⁺ CD38⁺ B cells (R7 and R1 and not R2); R1 and R2 refer to the gates of panel A. (C) Suppressor assay with freshly sorted autologous cell populations and CD3 alone or CD3+ IL-2. ■ indicate T cells alone; , T+ B-IgD⁺ CD38⁺⁺; and ▨, T+ B-IgD⁺ CD38⁺. Data represent mean plus or minus SEM of tonsils from 3 different donors.