Major histocompatibility complex class I chain-related protein
Major histocompatibility complex class I chain-related protein A (MICA) and B (MICB) are surface polymorphic proteins involved in innate immunity. They appear not to present antigenic peptides to T cells but this is controversial. However, they are believed to be stress molecules recognised by activating receptor NKG2D on natural killer cell and the T cell receptor on gamma-delta T cells. MICA and MICB genes are located within the HLA loci, but their protein products do not form dimers with beta2microglobulin. Mismatches in the MICA and MICB antigens can induce the production of alloantibodies, which have been associated with antibody mediated transplant rejection.