MIC-A (MHC class I chain-related gene A) is a single-pass type I member protein. It is expressed on the cell surface in gastric epithelium, endothelial cells and fibroblasts and in the cytoplasm in keratinocytes and monocytes. Additionally, MIC-A can be induced by bacterial and viral infections. A closely related protein, MICB, shares 85% amino acid identity with MICA. MICA is a ligand for human NKG2D, an activating receptor expressed on NK cells, NKT cells, gamma δ T cells, and CD8+ alpha beta T cells. Recognition of MICA by NKG2D results in the activation of cytolytic activity and/or cytokine production by these effector cells. MICA recognition is involved in tumor surveillance, viral infections, and autoimmune diseases.