MICA is a protein of 383 amino acids and interacts with the NKG2D receptor and the T cell receptor (TCR) to activate NK cells, αβ CD8 T cells, and γδ T cells. MICA is absent from most cells but is frequently expressed in epithelial tumors and can be induced by bacterial and viral infections. 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.