CD21 expression on human B cells from Hu-PBL mice engrafted with healthy donor cells. a and b Representative flow cytometry; Hu-PBL mouse is 28 days post engraftment. Gates and percentages of gated cells are indicated. c Spleen chimerism, and human lymphocyte subsets; day after engraftment as indicated. d CD21 expression, gated on human B cells with intermediate-to-high CD19 expression. MFI, mean fluorescence intensity, normalized to the human donor PBL control in each experiment. Shown are mean and SD; number of subjects is shown in parentheses; *p < 0.05.