CD275 is a 40 kD protein, also known as ICOS ligand, B7-RP1, B7-H2, and B7h. It is a member of the immunoglobulin receptor superfamily expressed on splenic B cells, dendritic cells, and macrophages. The expression of this antigen is increased by TNF-alpha stimulation and is highly upregulated by local inflammation. B7RP1 binds to ICOS and co-stimulates T cell and B cell responses. Two isoforms of this protein have been reported to occur as a result of alternative splicing. These isoforms show differential tissue distribution.