Treatment with rituximab or alemtuzumab reduced serum immunoglobulin levels. Xenochimeric mice were treated with either rituximab or alemtuzumab and levels of hIg in the circulation of the host mice were assessed by ELISA. (A) Expression of CD20 and CD52 by tonsillar PCs (CD19⁺CD38^bright, CD27^bright), GC B cells (CD19⁺CD38⁺, CD27⁺), and naive B cells (‘N', CD19⁺CD38^lo, CD27⁻). Isotype controls for B cells and for PCs are also shown. (B) Percentage of PCs isolated from blood (BD, n = 8), tonsil (TN, n = 5), LN (n = 5), spleen (SP, n = 6), and BM (n = 4) expressing CD20 or CD138. Error bars represent SEM. (C) Relative fluorescence intensity (MFI-positive cells − MFI-negative cells) of CD20 expression of PCs isolated from blood, tonsil, LN, spleen, and BM. Error bars represent SEM. (D) Frequency of tonsillar cells secreting either IgG, IgA, or IgM, assessed by ELISPOT. Mean of 3 experiments shown, error bars represent SEM. (E) Mean levels of hIgG, hIgM, and hIgA (ng/mL) in groups of untreated (Con), rituximab-treated (Rit), or alemtuzumab-treated (Cam) mice. Error bars represent SEM for treatment groups. (F) Mean levels of hIgG (ng/mL) in groups of untreated mice, xenochimeric mice treated with rituximab or alemtuzumab, and NOD/RAG^−/−/perforin^−/− mice treated with rituximab or alemtuzumab. Error bars represent SEM for treatment groups. Results are representative of 4 experiments.