Negatively regulates T-cell-mediated immune response by inhibiting T-cell activation, proliferation, cytokine production and development of cytotoxicity. When expressed on the cell surface of tumor macrophages, plays an important role, together with regulatory T-cells (Treg), in the suppression of tumor-associated antigen-specific T-cell immunity. Involved in promoting epithelial cell transformation. Expressed at the cell surface. A soluble form has also been detected. Expressed on the surface of professional antigen-presenting cells (at protein level). Widely expressed, including in kidney, liver, lung, pancreas, placenta, prostate, spleen, testis and thymus. Down-regulated upon activation of B-cells. N-glycosylated. Mice mount mildy augmented T-helper 1 responses and display slightly lowered parasitic burdens upon Leishmania major infection. Belongs to the immunoglobulin superfamily. BTN/MOG family.