Expression of pan–B-cell markers and activation antigens by functionally distinct populations of human B cells. Spleen MNCs were stained with anti-CD27, CD38, and CD20 mAb. The fourth channel was then used to assess expression of (A) the pan–B-cell molecules CD19, CD21, CD22, CD23, CD40, CD45, Bcl-2, and HLA-DR and (B) the activation molecules CD27, CD31, CD80, CD86, CD95 and CD138. Electronic gates (shown in Figure 1A-B) were set on naive, memory, and CD38⁺⁺CD20^± B cells. BM MNCs from different donors were stained with mAbs specific for CD20, CD38, and the indicated molecule, and an electronic gate set to identify BM PCs (CD38⁺⁺CD20^±). Dotted line represents negative control; solid line represents marker of interest. Histograms represent cells from 1 donor but are representative of those from multiple donors (n > 3).