Figure 1. Subsets of human developing B cells in FL and adult BM expressed low levels of CD27.

Typical flow cytometry diagrams of human developing B cell subsets in 19 wk FL (A) and adult BM (B) are shown. After exclusion of doublets and PI⁺ cells, CD19 and CD27 expression on CD45⁺FSC^loSSC^lo lymphocytes are shown (top row). CD19⁺CD27⁻ cells (R1) and CD19⁺CD27⁺ cells (R2) were further gated on CD19⁺CD10⁺ cells (R3 and R4, respectively) to identify developing B cells (second row). Those developing B cells were analyzed for surface IgM and IgD expression status to identify pro-/pre-B (IgM⁻IgD⁻; R5 and R6), immature B (IgM⁺IgD⁻), and transitional B (IgM⁺IgD⁺) cells (third row). Surface IgM⁻IgD⁻ cells (R5 and R6) were then analyzed by CD10 and CD34 expression to identify pro-B (CD10⁺CD34⁺) and pre-B cells (CD10⁺CD34⁻; bottom row). Figures near gating squares indicate frequencies of gated population within each diagram.