CD30 Ligand (CD30L)/TNFSF8, a type II membrane protein in the TNF superfamily, is expressed on activated T cells, B cells, monocytes, granulocytes, and medullary thymic epithelial cells. Its specific receptor, CD30/TNFRSF8, is a type I transmembrane glycoprotein in the TNF receptor superfamily. CD30 was initially identified as a cell surface antigen on Hodgkin's and Reed-Sternberg cells using the Ki-1 monoclonal antibody. It's also expressed on various non-Hodgkin's lymphomas, virus-infected T and B cells, and activated normal T and B cells. Among T cells, CD30 is preferentially expressed on subsets producing Th2-type cytokines and on CD4+/CD8+ thymocytes co-expressing CD45RO and IL-4 receptor. CD30L binding mediates diverse effects like cell proliferation, activation, differentiation, and apoptosis. CD30 can act as a co-stimulatory molecule in thymic negative selection and may play a crucial role in Hodgkin's disease and other CD30+ lymphomas. Human and mouse CD30 ligand cDNAs share 70% sequence homology.