MHC class I polypeptide–related sequence A (MICA) is a highly polymorphic cell surface glycoprotein encoded by the MICA gene located within MHC locus. MICA is related to MHC class I and it has similar domain structure, however, it is not associated with β2-microglobulin nor binds peptides as conventional MHC class I molecules do. MICA rather functions as a stress-induced ligand (as a danger signal) for integral membrane protein receptor NKG2D ("natural-killer group 2, member D"). MICA is broadly recognized by NK cells, γδ T cells, and CD8+ αβ T cells which carry NKG2D receptor on their cell surface and which are activated via this interaction.