May function in mediating immune cell-cell interactions. May act as a T-cell costimulatory molecule, enhancing anti-CD3-induced proliferation. May play a role in the interaction of dendritic cells with T-cells and the cells of the adaptive immune response. Expressed in spleen, lymph node, and tonsil. Lower expression in peripheral blood, bone marrow, and colon. No expression detected in thymus. Highly expressed in dendritic and B-cells.