Description: The H74 monoclonal antibody was generated and reacts with human B7-S1, also known as B7-H4 and B7x. Cross reactivity of this antibody to other proteins has not been determined. B7S1 is a newly discovered member of the B7 family. It is speculated that the costimulatory regulation of T cells by B7S1 is influenced by the activation status of B cells. While it is reported that BTLA is a counter receptor for B7S1, further studies are needed to definitely determine the B7-H4 ligand. H74 stains human B7-H4 transfected cells and not peripheral blood cells. Exact expression pattern of B7-H4 has not been fully characterized.