Flow cytometric analysis of human B-lineage cell lines with the MoAbs. A pro–B-cell line RS4;11, a pre–B-cell line HPB-NULL, and a B-cell line LBW-4 were stained by the indicated MoAbs in the cytoplasm (A) and on the cell surface (B). For cytoplasmic staining, 0.05% of saponin was added to the staining buffer. Cells were first incubated with the MoAbs and then with PE–anti-mouse κL chain antibody. The fluorescence intensity of the stained cells was analyzed by a flow cytometer. The thin dotted-line histograms indicate control staining with an isotype-matched control MoAb whereas the thick solid-line histograms indicate staining with MoAbs specific to λ5, VpreB, pre-BCR, μH chain, κL chain, or λL chain. All data including other cell lines are summarized in Table 1.