Abstract: An isolated polynucleotide encoding a novel immunoglobulin superfamily member named GP286 is provided. GP286 has a predicted single membrane spanning domain and one immunoglobulin (Ig) domain in the extracellular portion of the protein. The protein structure and tissue distribution of GP286 indicate that it plays a role in cell-cell recognition, binding, signaling and adhesion events in the immune system. Provided by the invention are isolated GP286 related polynucleotides and polypeptides, vectors, and host cells comprising any of the above, antibodies directed to GP286, cells which produce such antibodies, and related diagnostic and therapeutic methods.