While influences of the genetic HLA-E dimorphism on graft-vs.-leukemia reactions after hematopoietic stem cell transplantation, spontaneous abortions, viral infections, and susceptibility to autoimmune diseases have been described elsewhere (39–42), we will focus here on features of HLA-E proteins related to the formation of ligands for CD94/NKG2A/C NK receptors. This evidence concerns the gene HLA-E and viral infectious disease.