Cell surface receptor that may play a role in the innate and adaptive immune response. Acts as a counter-receptor for CD276 and interaction with CD276 on T-cells enhances T-cell activation. Interacts with CD276 and this interaction enhances T-cell activation. Detected in cultured B-cells, T-cell leukemia and monocyte leukemia. Expressed constitutively on CD8 T-cells and induced on CD4 T-cells after activation. Induced in CD4 T-cells by concanavalin-A.