Identification of naive, memory, and CD38⁺⁺CD20^± B cells. Human BM (A) and spleen MNCs (B-C) labeled with anti-CD20, anti-CD27, and anti-CD38 mAb. (A-B) ISCs were identified as CD38⁺⁺CD20^±; total B cells were CD38^dimCD20⁺. (C) The total B-cell population was further resolved into naive and memory subsets by the differential expression of CD27. Splenic CD38⁺⁺CD20^± (D), naive (E), and memory (F) B cells were isolated by sorting and were Giemsa stained. The arrow in panel D indicates an example of a cell with a clear perinuclear zone and condensed chromatin. Original magnification, × 100. Values represent the mean FSC and SSC (± SEM; n = 28) of the 3 B-cell populations. (G-J) Immunofluorescence staining was performed on spleen sections obtained from a healthy donor using anti-IgM (red; G-H) or in combination with anti-CD20 mAb (green; I-J). Follicular (FO) and red pulp (RP) areas, as well as ISCs (arrows), are indicated. Original magnifications: × 5 (G,I), × 20 (H,J).