Functional characterization of CD10^pos and CD10^neg FL-T_FH. (A) FL LN or reactive tonsil (Tons) cells were stimulated with phorbol 12-myristate 13-acetate and ionomycin for 6 hours, and with brefeldin A for the last 4 hours of stimulation before intracytoplasmic detection of cytokines. The percentage of singlet viable CD10^neg (gray) or CD10^pos (white) viable T_FH producing IL-21, IL-17A, IL-4, and IFN-γ was determined. *P < .05, **P < .01. (B) Representative plots of IFN-γ/IL-4 and CD10/TNF-α staining on FL-T_FH. (C) Purified malignant FL B cells were cultured alone (Ø), with an activation cocktail (recombinant human CD40 ligand, IL-2, and IL-4), or in the presence of autologous CD10^neg or CD10^pos T_FH at a 1:1 ratio for 48 hours. Representative plots of active caspase-3 staining gated on CD20^pos B cells (n = 3).