Memory B cells, plasmablasts, and serum immunoglobulins in hu-mice expressing mBAFF or hBAFF. (A) Representative flow cytometric analysis of CD38 and CD24 expression (top plots) on hCD45⁺CD20⁺ from human PBMCs and from spleen of BRGS and hBAFFKI-BRGS hu-mice (after gating out CD38^vhigh PBs by Boolean gate as shown in Figure 4A). The plots show the gating of CD38^lowCD24^high memory B cells, CD38^highCD24^high immature/transitional B cells, and CD38^lowCD24^low naive mature B cells. The bottom histograms confirm low CD10 expression on memory B cells relative to the high expression on immature/transitional B cells. (B) Representative flow cytometric analysis of CD38 and CD10 expression (top plots) on total hCD45⁺CD20⁺ spleen cells showing the gating of CD38^vhighCD10⁻ plasmablasts. The bottom histogram confirms no CD24 expression on the gated plasmablasts (PBs) relative to the high expression on immature/transitional B cells (gated as CD38^highCD24^high). (C) Representative flow cytometric analysis to identify plasma cells in the spleen of hu-mice. Splenic hCD45⁺CD19⁺ cells were first gated for high expression of intracellular (IC) Igκ or Igλ (top plots, shown with biexponential axes). These latter (IC IgL-high⁺) cells were then gated for high expression of CD38 (bottom plots). (D-E) Scatter plot analyses of the percentage of CD38^lowCD24^low naive mature B cells (x-axis) relative to the percentage of CD38^lowCD24^high memory B cells (y-axis) within the CD20⁺ (-PB) cell population (D), and of the percentage of CD10^– mature B cells (as in Figure 4A) within CD20⁺ (-PB) cells (x-axis) relative to the percentage of CD38^vhighCD10⁻ plasmablasts (y-axis) within all CD20⁺ cells (E) in individual BRGS (□) and hBAFFKI-BRGS (▪) hu-mice. The linear regression analyses were performed on all data. (F) Frequencies of memory B cells (identified as in panel A) in the CD20⁺ (-PB) splenic B-cell population (left) and absolute cell numbers (right) in individual BRGS and hBAFFKI-BRGS hu-mice. (G) Frequencies of plasmablasts (identified as in panel B) within CD20⁺ splenic cells (left) and absolute cell numbers (right). (H) Frequencies of plasma cells (identified as in panel C) within CD19⁺ splenic cells (left) and absolute cell numbers (right). (I) Total IgM and IgG concentrations in serum of BRGS and hBAFFKI-BRGS hu-mice. Each symbol in panels D through I represents a mouse; bars are mean and SEM. N = 16 to 23 mice per group and 4 different CB groups. *P < .05; **P < .01.