Analysis of B cells and immunoglobulin production in hu-PBL mice expressing either mBAFF or hBAFF. Hu-PBL mice expressing either mBAFF (M) or hBAFF (H) were analyzed 2 to 3 weeks after transplantation of human PBMCs into BRGS and hBAFFKI-BRGS mice, respectively. (A) Representative analysis of CD19 expression on hCD45⁺ cells. Numbers indicate the frequency of CD19⁺ B cells. (B) Frequency of CD19⁺ B cells within the hCD45⁺ leukocyte cell population (left) and absolute CD19⁺ cell numbers (right) in individual hu-PBL mice, with mean and SEM in each group of mice. (C) Representative flow cytometric analysis of CD19 and CD38 expression on CD19⁺ cells from human PBMCs and spleen of hu-PBL mice. Gates were drawn around CD19⁺CD38^low mature B cells (naive and memory) and CD19^lowCD38^high plasmablasts and plasma cells. Numbers indicate frequency of each cell population. (D) Frequency of CD19⁺CD38^low mature (naive and memory) B cells (left) and of CD19^lowCD38^high plasmablasts and plasma cells (PBs&PCs; right) within the CD19⁺ cell population of each hu-PBL mouse, with mean and SEM for each group of mice. (E) CD19⁺CD38^low and CD19^lowCD38^high absolute cell numbers in the spleen of individual hu-PBL mice expressing mBAFF (left) or hBAFF (right). Each symbol represents an individual mouse and lines connect values obtained from the same animal. Statistical differences were analyzed by paired Student t test. (F) Serum IgM and IgG levels in hu-PBL mice expressing mBAFF (M) or hBAFF (H). Data in all graphs were combined from 4 independent experiments (with 4 donor PBMCs) and a total of 8 to 13 hu-PBL mice per group. *P < .05. ns, not significant.