Characterization of CD10^pos T cells in B-cell lymphomas. (A) Double staining revealed the presence of scattered strong CD10^pos cells within FL neoplastic follicles. Numerous CD10^pos (brown) PAX5^neg (red) lymphocytes are evidenced (arrows). Original magnification: objective ×20 (left) and ×40 (right). (B) Representative characterization of ICOS, CD10, CXCR5, and PD-1 staining by flow cytometry on CD3^posCD4^pos viable cells from FL LNs. (C) In situ characterization of CD10^pos T cells in RLH including reactive LNs and tonsils, and B-cell lymphomas with follicular growth pattern (MCL, NLPHL, and FL). For each sample, the numbers of CD10^posPAX5^neg and PD-1^pos cells found inside GCs were counted in 10 high power fields (×40), and the median of these 10 values was calculated. Data are expressed as the median [range] of the different samples tested. ND, not done. (D) Expression of MME/CD10 in CD3^posCD4^pos CXCR5^highICOS^highCD25^neg T_FH purified from 7 reactive tonsils and 7 FL samples (203435_s_at probeset of the GeneChip HG-U133 Plus 2.0 oligonucleotide arrays). **P < .01. (E) Frequency of CD10^pos T_FH among CD4^pos T cells in 15 FL LNs and 25 reactive tonsil samples, evaluated by flow cytometry. ***P < .001.