Cytometric identification of B and T cells. (A) GC B cells were identified from among CD19⁺ total tonsillar B cells using IgD and CD38 as previously described.³⁹  Naive B cells were isolated by first gating on IgD⁺CD38⁻ cells (naive-enriched) followed by IgM⁺ and CD27⁻ gating (IgM⁺IgD⁺CD38⁻CD27⁻). (B) Tonsillar T and B cells, PBL B cells, and tonsillar GC and naive B cells were stained with RO and RA antibodies. T-cell RO expression levels were used to subdivide B cells into RO⁻, RO^+/−, and RO⁺ fractions. Numbers represent the percentage of cells within each RO fraction. (C) RO expression levels were determined for tonsillar total B, GC, and naive B-cell pools. Results from 5 tonsils are presented, including the average value data point (horizontal crossbar). Percentages represent the distribution of each subset across each RO fraction. (D) The percentage of GC B cells among the total number of B cells within a given RO fraction. Equivalent data were collected from 5 tonsils. For example, GC B cells account for only 12.6% of all RO⁺ tonsillar B cells. (E) Tonsillar GC B cells were stained with the addition of anti-CD77. The correlation between RO and CD77 expression was quantified among gated tonsillar total, naive, and GC B cells. Note that most naive B cells are double-negative for both markers.