Immature B-cell markers expressed by adult bone marrow and term cord-blood B cells. (A) Bone marrow CD19⁺ B cells were gated into CD21^- immature and CD21⁺ mature fractions and the differential expression of CD10, CD38, CD44, and CD24 was assessed relative to isotype matched control mAb (Con Ig). (B) Bone marrow CD19⁺ B cells were gated into CD38^neg/lo mature B cells and a CD38^hi immature subset. A fraction of the latter express CD20 more densely and both IgM and IgD. (C) Differential expression of CD5 and CD10 by bone marrow IgD^- CD38^hi pro/pre B cells and IgD⁺ CD38^hi immature B cells. (D) Cord blood CD19⁺ B cells were gated into CD21^neg/lo and CD21⁺ fractions, and the differential expression of immature bone marrow markers was assessed. Results are representative of 2 bone marrow aspirates and 10 cord blood samples.