CD27 (TNFRSF7) is a member of the TNF-receptor superfamily limited to cells of the lymphoid lineage and exists as both a dimeric glycoprotein on the cell surface and as a soluble protein in serum. As a T and B cell co-stimulatory molecule, the activity of CD27 is governed by its TNF-like ligand CD70 on lymphocytes and dendritic cells. The CD27-CD70 interaction is required for Th1 generation responses to differentiation signals and long-term maintenance of T cell immunity, and meanwhile, plays a key role in regulating B cell differentiation, activation and immunoglobulin synthesis. The CD27 receptor transduces signals and subsequently leads to the activation of NF-κB and MAPK8/JNK, mediated by the adaptor proteins TRAF2 and TRAF5. In addition, the proapoptotic protein SIVA is capable of binding the cytoplasmic tail of CD27 and exerts action in the process of apoptosis.