CD8A and Behcet disease: Individual amino acid residues located on HLA-B51 molecules are associated with disease and are located in the antigen binding regions mediating peptide binding and interactions between CD8 lymphocytes, Natural killer (NK) cells and MHC class I (MHC-1) molecules.12 Studies have also shown an association between BD and the MHC Class I polypeptide-related sequence A (MICA) allele 009.