Involved in the costimulatory signal essential for T-cell proliferation and IFNG production in a PDCD1-independent manner. Interaction with PDCD1 inhibits T-cell proliferation by blocking cell cycle progression and cytokine production. Interacts with PDCD1. Expressed in immature and mature bone marrow-derived dendritic cells and splenic dendritic cells. Highly expressed in placenta, liver and weakly expressed in heart, spleen, lymph nodes and thymus. Also expressed in some tumor cell lines of lymphoid origin. Belongs to the immunoglobulin superfamily. BTN/MOG family.