CD137 in T lymphocytes helps to regulate activation, proliferation and apoptosis. CD137 and CD28 are co-stimulatory molecules of T cell activation. It plays an important role in regulating T-cell-dependent immune responses. The expression of CD137 correlates negatively with lymphocyte proliferation and induces cell death caused by mitogen overstimulation. In monocytes, CD137 induces activation, promotes adherence and helps in prolongs survival.