HLA-G remains a mystery.
In this brief summary, we argue that many widely held beliefs about HLA-G are questionable. Recent research has led to a re-evaluation of many of the characteristics that were thought to make HLA-G unusual among the MHC class I molecules. First, contrary to reports suggesting that the gene encoding HLA-G exhibits marked polymorphism in some human populations, recent data have shown that the HLA-G gene has comparatively little polymorphism - a feature that might allow it to be expressed in the placenta without causing rejection by the maternal immune system. Second, although truncated forms of HLA-G are generated in the placenta, most of them are unlikely to have significant biological effects as they do not reach the cell surface. Third, the hypothesis that a major role of HLA-G is to prevent attack of the placenta by maternal natural killer cells is now the subject of renewed scrutiny. Finally, there is little evidence that the induction of expression of HLA-G is a major mechanism by which tumor cells avoid immune attack. HLA-G has once again become as mysterious as when it was discovered: an MHC class I molecule expressed at a challengingly extraordinary site--the immunologically uneasy interface between mother and fetus.
Bainbridge
D
D
Royal Veterinary College, 44 Hawkshead Rd, Potters Bar, UK EN6 1NB. dbainbridge@rvc.ac.uk
Ellis
S
S
Le Bouteiller
P
P
Sargent
I
I
D000818:Animals; D006680:HLA Antigens / Q000276:immunology*; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I / Q000276:immunology*; D006801:Humans; D007694:Killer Cells, Natural / Q000276:immunology; D009369:Neoplasms / Q000276:immunology; D011110:Polymorphism, Genetic / Q000276:immunology; D020033:Protein Isoforms / Q000276:immunology
D006680:HLA Antigens; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I; D020033:Protein Isoforms