Combination of surface markers CD45RB and CD69 defines new MBC subsets in tissues. Splenocytes were stained for flow cytometric analysis with “Stain 2” (supplemental Table 2). (A) Distribution of CD45RB and CD69 of CD19⁺ CD27^– and CD19⁺ CD27⁺ B cells of depicted donor spleens. The magenta letters and numbers show the sex (F = female; M = male) and the age (in years) of the donor. Numbers next to outlined areas indicate percentage of cells in gated populations. The indicated staining results in up to 4 different subsets, CD45RB SP, CD45/CD69 DP, CD69 SP, and CD45/CD69 DN. (B, left panel) CD45RB/CD69 distribution of human CD19⁺ CD27⁺ singlets within spleen, blood, BM, lymph nodes (LN), tonsil, or intestinal tissue (Gut) of indicated donors by utilizing “Stain 2” and “Stain 3” (supplemental Table 2). (B, right panel) shows the summary of CD45RB/CD69 distribution of CD19⁺ CD27⁺ MBCs within 21 spleen, 15 blood, 18 BM, 10 LN, 3 tonsil, and 14 gut samples. Asterisks indicate significant differences in CD45RB/CD69 subset distribution of indicated tissues compared with spleen using the unpaired two-tailed Student t test with Welch’s correction.