CD45 was heterogeneously expressed on myeloma cells and correlated with IL-6 dependency. (A) IL-6–dependent myeloma cell lines ILKM-2 and ILKM-3 were stained for 30 minutes by PE-Cy5-CD45 (forward scatter) and FITC-38 (side scatter) and analyzed by cell sorter (top panels), and growth curves are shown of the cells cultured in medium alone (solid lines) or in the presence of IL-6 (2 ng/mL; dotted lines) for the indicated period of time (bottom panels). (B) CD45 expression (top) and growth curves (bottom) of the IL-6–independent cell lines KMS-5 and U-266.