Expression of Muc-1 core protein on MM patient and normal donor B cells. Peripheral blood B cells from 2 representative MM patients (A) and 2 representative normal donors (B) are shown, with Muc-1 staining plotted as a histogram. The bold line shows Muc-1 staining on B cells, and the thin line shows isotype-matched control staining on an identically gated aliquot of cells. Shown are B cells (26% to 32% and 4% to 7% for MM patients and normal donors, respectively), which include SSc^hi gated PB B cells for MM patients, because these are clonotypic, having IgH and CD19 transcripts.32,34,35 In contrast, SSc^hi PB B cells are excluded from the B-cell gate in normal donors, because these are monocytes.35