Flow cytometric analysis of CD19⁺CD27⁺CD43⁺ cells in human neonatal cord blood, peripheral blood, and tonsil samples. (A–C) CD27⁺CD43⁺ cells (red) were defined within CD19⁺ lymphocytes (blue; left plots). Where illustrative, the CD19⁻ lymphocytes (T cells and NK cells) are shown in yellow. Samples were also stained with anti-CD3, anti-CD5, and anti-CD38 as indicated. The right plots only display CD19⁺CD3⁻ events. Data are representative of 4 cord blood, 27 blood, and 7 tonsil samples. (D) Frequencies of CD27⁺CD43⁺ cells among CD19⁺ cells in neonatal cord blood and peripheral blood samples from individual children and adults of indicated ages. The relative contributions of CD3⁺ T cells, CD3⁻CD38^hi plasma cells, and CD3⁻CD38^low B lymphocytes are indicated for each individual. (E) Frequencies of CD43⁺, CD43⁻IgM⁺, and CD43^-IgM⁻ cells among CD19⁺CD27⁺CD3⁻CD38^low cells within the blood of healthy adults. Individual frequencies are shown in gray and the median is indicated with a red bar. IgM expression was detected with a monoclonal IgM-HorizonV450 antibody (clone G20-127).