Proliferation of Immature Myeloma Cells by Interleukin-6 Is Associated with CD45 Expression in Human Multiple Myeloma

Multiple myeloma (MM) is a hematologic malignancy of human plasma cells, and myeloma cells can be classified into several subpopulations according to phenotypic differences, such as CD38+++MPC-1+CD49e- immature, CD38+++MPC-1+CD49e- intermediate and CD38+++MPC-1+CD49e+ mature myeloma cells. The expression of the CD45 molecule on myeloma cells is quite variable, and the physiological consequence of CD45 on myeloma cells is still unknown. Recently, we have found that a few MPC-1- immature myeloma cells express CD45 antigens while most myeloma cells do not express the CD45. MPC-1-CD45+CD49e- but not MPC-1-CD45-CD49e-immature cells contain proliferating cells in response to interleukin-6 (IL-6). IL-6 can also induce expression of CD45 on the MPC-1-CD45- subpopulation of immature myeloma cells. In addition, myeloma cell lines responding to IL-6 express CD45, whereas cell lines proliferating independent of IL-6 do not express CD45. In the U266 cell line, IL-6 leads to the induction of CD45 expression and cell pr...