Description: The HK5.3 monoclonal antibody reacts with mouse B7RP-1, also known as B7h, B7-H2, GL50 and ICOS Ligand. B7RP-1, a member of the B7 family, has a predicted molecular weight of ~40 kDa and belongs to the Ig superfamily. Mouse B7RP-1 is expressed by antigen presenting cells including B cells, monocytes/macrophages and dendritic cells. B7RP-1 binds to the ICOS molecule (AILIM, CRP-1) expressed by activated T cells. The interaction of ICOS/B7RP-1 plays an important role in the T cell costimulation pathway.