Detection of HLA-E and -G DNA alleles for population and disease studies

HLA-E and -G genes show a restricted polymorphism encoding for molecules wh ose variability is limited at the peptide binding site. Fourteen alleles th at give rise to only three productive proteins for HLA-G (*0101, *0103 and *0104) and five alleles with three different proteins for HLA-E ("0101, *01 02 and *0103) have been described. Expression of these molecules is low and found in many tissues for HLA-E; HLA-G protein is expressed in extravillou s trophoblast cells and thymic epithelium. Molecular studies have shown how HLA-G and HLA-E bind to natural killer (NK) cells immunoglobulin and lecti n-type inhibitory receptors. HLA-E may act as a sentinel of the cell; if cl assical class I and HLA-G are being expressed, HLA-E molecules may reach th e cell surface and inhibit the lysis by NK cells. Most findings are consist ent with the hypothesis that HLA-E and -G proteins may be tolerogenic molec ules at either the T-cell receptor (TcR) (inflammation, graft rejection) or NK level, switching off cells which usually attack foreign (including foet us) or self (autoimmune) antigens. A lour HLA-E and -G polymorphism is obse rved in humans, and their allele frequencies are mostly homogeneous in the populations tested so far. Many studies to detect these alleles are now bei ng performed in isolated populations and also in pregnancy-associated patho logies. In the present paper, standard and detailed techniques to detect HL A-E and -G DNA polymorphism are reported and discussed.