MICB (MHC Class I Polypeptide-Related Sequence B) is a gene that encodes a stress-induced protein involved in immune system activation. It serves as a ligand for the NKG2D receptor on natural killer (NK) cells and some T cells, helping the immune system recognize and respond to infected or transformed cells. MICB expression increases under conditions of cellular stress, such as viral infection or tumor development, promoting immune surveillance and targeted cell destruction.