Expression profiles for B lineage genes and intracellular proteins in pro-B and pre-B subpopulations.

(A) Human CD34⁺CD19⁺VpreB⁻pro-B, CD19⁺ κ/λLC⁻VpreB⁺pre-B, and CD19⁺κ/λLC⁻CD34⁻VpreB⁻pre-B cells were isolated from fetal bone marrow samples. (B) Mouse CD19⁺ VpreB⁺ and CD19⁺VpreB⁻ pro-B cells were isolated from RAG2^−/− bone marrow, and VpreB⁺ and VpreB⁻ subpopulations of pre-B cells (CD19⁺BP-1⁺ κ/λLC⁻) were isolated from bone marrow of wild-type juvenile mice. Subpopulations were purified by 2 rounds of immunofluorescence-based sorting, and the sorted cells were used as templates for RT-PCR assays. PCR products were visualized on agarose gels by ethidium bromide staining. (C) Analysis of cytoplasmic VpreB, Igβ, and conventional LC protein expression within pre-BCR⁻ pre-B cells. Dashed lines indicate staining of pre-BCR⁻ cells. Solid lines represent staining in control pre-BCR⁺ cells (i) and CD19⁺κ/λLC⁺ B cells (ii) and (iii). Background staining with isotype-matched antibodies of irrelevant specificity is indicated by shaded histograms.