Cytometric identification of tonsillar GC B cells and quantification of surface CD45RB expression. (A) Human tonsillar B cells were cytometrically identified using procedures previously described.⁷  Gates Q1 (CD38⁺IgD⁻), Q2 (CD38⁺IgD⁺), Q3(CD38⁻IgD⁺), and Q4(CD38⁻IgD⁻) were determined for total tonsillar B cells based on distinct staining patterns using antibodies against CD38 and IgD. (B) GC B cells were identified from Q1 as CD38⁺IgD⁻ and excluded CD38⁺⁺ cells. An anti-CD27 antibody was used to further identify the Pblast pool from Q1 as IgD⁻CD38⁺⁺CD27⁺. Antibodies against IgM and/or CD27 were used to identify the pre-GC (from Q2 as IgM⁺IgD⁺CD38⁺CD27⁻), naive (from Q3 as IgM⁺IgD⁺CD38⁻CD27⁻), and memory (from Q4 as IgD⁻CD38⁻CD27⁺) B-cell pools. (C) Tonsillar B cells were additionally stained with anti-CD45RB. The percentage of RB⁺ cells within each B-cell subset is indicated. Values represent the average of 6 tonsils. Standard deviations are included as error bars. Intersubset differences in the percentage of RB⁺ cells were statistically significant (P ≤ .01, denoted by a double asterisk [**]) between GC and all other subsets.