MHC class I polypeptide-related sequence A, also known as MIC-A, PERB11.1 and MICA, is a single-pass type I membrane protein which belongs to the MHC class I family of MIC subfamily. MICA contains one Ig-like C1-type domain and is expressed on the cell surface, although unlike canonical class I molecules does not seem to associate with beta-2-microglobulin. It is thought that MICA functions as a stress-induced antigen that is broadly recognized by NK cells, NKT cells, and most of the subtypes of T cells. MICA is the ligand for NK cell activating receptor KLRK1/NKG2D. MICA seems to have no role in antigen presentation. MICA leads to cell lysis by binding to KLRK1.