Heterogeneous MHC class I molecule expression on freshly isolated CD38⁺ and CD138⁺/CD38⁺ bone marrow myeloma cells. Staining profile of MHC class I expression on patients 2, 3, 4, 5, 6, and 10 derived CD38⁺ cells are reported in panels i, ii, iii, iv, v, and vi, respectively (A). It should be noted that in patients 2 and 3 the myeloma cells were stained equally well by either anti-CD38 or anti-CD138 mAbs; for p10 MHC class I expression was tested on immunomagnetic-purified CD38⁺/CD138⁺ myeloma cells, and for patients 4, 5, and 6 CD38^bright cells were gated. At least 10 000 events were analyzed within the CD38^+bright or the CD38⁺/CD138⁺ gated cells. Open curves are the isotypic control; close curves are W6-32 staining. The correlation between myeloma clinical stages and MHC class I expression was analyzed (B). Stage IIA (n.4), stage IIB (n.2), stage IIIA (n.5), and stage IIIB (n.3). The differences between stage IIB and IIIB reached statistical significance with P of 05 or less. The analysis was performed via gating on living MHC class I-positive myeloma cells.