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. Overexpressed in breast, ovarian, endometrial, renal cell (RCC) and non-small-cell lung cancers (NSCLC). Expressed on activated T- and B-cells, monocytes and dendritic cells, but not expressed in most normal tissues (at protein level). Widely expressed, including in kidney, liver, lung, ovary, placenta, spleen and testis. Up-regulated by IL6/interleukin-6 and IL10/interleukin-10 and inhibited by CSF2/GM-CSF and IL4/interleukin-4 on antigen-presenting cells (APCs). N-glycosylated. May serve as a predictive marker for renal cell carcinoma. Belongs to the immunoglobulin superfamily. BTN/MOG family. The mouse ortholog has been shown to be a GPI-anchored protein but the Gly residue which is predicted to be the modified site in mouse and rat is not conserved in human.