Human B7-H2, also called B7RP-1, B7h, LICOS, and GL50, is a member of the growing B7 family of immune costimulatory proteins. Other family members include B7-1, B7-2, B7-H1 (PD-L1), PD-L2, and B7-H3. B7 proteins are members of the immunoglobulin (Ig) superfamily, the extracellular domains contain 2 Ig-like domains and all members have short cytoplasmic domains. Among the family members, they share about 20-25% amino acid identity. Human and mouse B7-H2 share approximately 49% amino acid identity.

B7-H2 has been identified as the ligand for ICOS, a member of the CD28 family of costimulatory receptors. Human B7-H2 is a 309 amino acid (aa) protein with a putative 18 aa signal peptide, a 239 aa extracellular domain, an 18 aa transmembrane region, and a 33 aa cytoplasmic domain. Human B7-H2 is expressed constitutively on resting B cells, dendritic cells, and at low levels on monocytes. The B7-H2/ICOS interaction appears to play roles in T cell dependent interaction appears to play roles in T cell dependent B cell activation and T Helper (Th) cell differentiation.