CD137 (ILA/4-1BB), expressed by primary human monocytes, induces monocyte activation and apoptosis of B lymphocytes

Human CD137 is a member of the tumor necrosis factor (TNF) receptor family and the homologue of murine 4-1BB, Recent studies have demonstrated that CD 137 promotes accessory T cell activation, and regulates proliferation and s urvival of T lymphocytes, This study reports on the expression and function of CD137 in peripheral blood monocytes, While monocytes showed constitutiv e expression in 10 out of 18 healthy donors, CD137 was not expressed on res ting T or a lymphocytes. Immobilized antibodies to CD137 markedly induced t he production of IL-8 and TNF-alpha protein and mRNA, and led to inhibition of IL-10 expression by primary monocytes. Furthermore, cross-linking of CD 137 on monocytes resulted in an increase of B lymphocyte apoptosis mediated by direct cell-cell contact of both cell populations. In conclusion, this study identified CD137 as a new receptor involved in monocyte activation by inducing a characteristic cytokine release profile. In addition, CD137 may play a role in monocyte-dependent control of B lymphocyte survival.