Background：

HLA-E belongs to the HLA class I heavy chain paralogues. This class I molecule is a heterodimer consisting of a heavy chain and a light chain (beta-2 microglobulin). The heavy chain is anchored in the membrane. HLA-E binds a restricted subset of peptides derived from the leader peptides of other class I molecules. The heavy chain is approximately 45 kDa and its gene contains 8 exons. Exon one encodes the leader peptide， exons 2 and 3 encode the alpha1 and alpha2 domains， which both bind the peptide， exon 4 encodes the alpha3 domain， exon 5 encodes the transmembrane region， and exons 6 and 7 encode the cytoplasmic tail.