NKG2D is a type 2 transmembrane protein with an extracellular C-type lectin-like domain. It forms a homodimeric cell-surface receptor on immune cells. Murine NKG2D binds to a set of ligands that have sequence and structural similarity to class 1 major histocompatibility complex proteins. Binding of NKG2D to a ligand triggers a signaling cascade that promotes effector functions in the immune cell that expresses NKG2D. NKG2D does not signal directly, but exists in a complex with adaptor proteins that mediate signaling upon ligand binding. As NKG2D is expressed on cytotoxic cells including natural killer cells and CD8+ lymphocytes, this activation can promote the cytotoxic destruction of the cell expressing the ligand for NKG2D by the cell expressing NKG2D.