Lack of MHC-G4 and soluble (G5, G6) isoforms in the higher primates, Pongidae

HLA-G is a class Ib (nonclassical) major histocompatibility complex (MHC) p rotein expressed at the materno-fetal interface that may inhibit natural ki ller (NK) cell-mediated lysis in an allotype-independent manner. The human MHC-G transcript is differentially spliced, giving rise to at lease six dif ferent forms. Tn order to study the evolutionary importance of this phenome non, the presence of alternative splicing in MHC-G mRNA molecules from Pong idae (Chimpanzee, Gorilla, and Orangutan) has been investigated in the pres ent work, and three alternative spliced isoforms (i.e.: G1, G2, and G3) hav e been found, but not the G4 and the soluble G5 and Gb ones. In addition, a novel MHC-G isoform is de scribed in Gorilla, "G2 short." This molecule is similar to the G2 isoform, but it lacks 29 amino acids normally encoded by exon 4. Our findings suggest that soluble isoforms are not necessary for M I-IC-G function(s) in Pongidae or that MHC-G is not a functional protein, b ecause G1 is not necessary for survival in humans and Cercopithecinae bear stop codons in MHC-G exon 3. (C) American Society for Histocompatibility an d Immunogenetics, 2000. Published by Elsevier Science Inc.