Involvement of the Cytokine Receptor CD137 in Murine Hematopoiesis

CD137 and CD137 ligand are members of the tumor necrosis factor (TNF) receptor and TNF family, respectively. CD137 is expressed by cells in the bone marrow and CD137 ligand is expressed on hematopoietic progenitor cells. The interaction of CD137 and CD137 ligand induced proliferation and colony formation of hematopoietic progenitor cells and their differentiation to macrophages. Since CD137 is expressed on activated immune cells the CD137-induced myelopoiesis may take place during ongoing immune responses. However, in a steady-state condition the CD137 receptor/ligand system seems to inhibit myelopoiesis. Current data only indicate an involvement of CD137 and its ligand in myelopoiesis while other hematopoietic lineages are not affected.