INTERLEUKIN 10 (IL-10) UP-REGULATES FUNCTIONAL HIGH-AFFINITY IL-2 RECEPTORS ON NORMAL AND LEUKEMIC B-LYMPHOCYTES

Interleukin 10 (IL-10) has recently been shown to induce normal human B lymphocytes to proliferate and differentiate into immunoglobulin (Ig )-secreting cells. Herein, we show that IL-10 also promotes DNA synthe sis and IgM production by anti-CD40 activated B cell chronic lymphocyt ic leukemia (B-CLL). Most strikingly, IL-2 and IL-10 were found to syn ergize to induce the proliferation and differentiation of B-CLL cells. This synergy between IL-2 and IL-10 was also observed with normal B c ells which proliferated strongly and secreted large amounts of IgM, Ig G, and IgA. The observed synergy is likely to be due to the IL-10-indu ced increase of high affinity IL-2 receptors on both normal and leukem ic B cells. This increase of high affinity receptor is associated to a n increase of Tac/CD25 expression that can be detected by flow cytomet ric analysis. Taken together, these results indicate that IL-10 permit s anti-CD40 activated B cells to respond to IL-2 through an induction of high affinity IL-2 receptors. This effect of IL-10 may partly expla in how T cells, which activate B cells in a CD40-dependent fashion, in duce B cell proliferation and differentiation mostly through IL-2.