Mouse B7-H2, also called CD275, B7RP-1, B7h, LICOS and GL50, is a member of the growing B7 family of immune costimulatory proteins. CD275 has been identified as the ligand for ICOS, a member of the CD28 family of co-stimulatory receptors. Mouse CD275 is expressed on resting B cells and at low levels on monocytes. The CD275/ ICOS interaction appears to play roles in T cell dependent B cell activation and Th differentiation.