Evolution of MHC-G in primates: a different kind of molecule for each group of species.
When MHC-G molecules in primates (New World and Old World monkeys, Anthropoids and humans) were compared phylogenetically, very different evolutionary patterns within each species were found; their molecules did not have a straight forward and linear development throughout the postulated evolutionary pathway of primates. The earlier New World monkeys (South America) had relatively more alleles and the polymorphism was placed in the T-cell receptor (TcR), NK receptors and antigen binding sites; MHC-G probably works as a classical class I presenting molecule in these monkeys. MHC-G intron 2 from New World monkeys does not show the typical 23 bp deletion found in all other more recent primate species. Thus, it is possible that MHC-G molecules in New World monkeys belong to a different lineage than the MHC from higher primates. Another early lineage, Eurasian Old World monkeys, shows stop codons at exon 3: MHC-G proteins lacking the alpha2 domain may functionally suffice or otherwise reading-through stop-codon translational mechanisms may exist, as shown for other genes. Orangutans show lower (but significant) polymorphism than New World monkeys at NK, TcR and antigen binding regions; gorilla and chimpanzee show very low polymorphism. Humans only show three different HLA-G proteins with changes not affecting NK, TcR or antigen binding sites. It is observed that the more exposed the mother to allogeneic fetuses (polygamy), the less polymorphic HLA-G is observed within a given species. The data are concordant with the postulated immune inhibitory function for MHC-G in Old World monkeys, anthropoids and humans both at placental and inflammatory level.
Arnaiz-Villena
A
A
Department of Immunology, Hospital 12 de Octubre, Universidad Complutense, Madrid, Spain. antonio.arnaiz@inm.h12o.es
Morales
P
P
Gomez-Casado
E
E
Castro
M J
MJ
Varela
P
P
Rojo-Amigo
R
R
Martinez-Laso
J
J
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D002522:Chlorocebus aethiops; D018076:DNA, Complementary; D019143:Evolution, Molecular; D006071:Gorilla gorilla; D006801:Humans; D008252:Macaca fascicularis; D008253:Macaca mulatta; D008285:Major Histocompatibility Complex / Q000235:genetics* / Q000276:immunology; D008969:Molecular Sequence Data; D019974:Pan paniscus; D002679:Pan troglodytes; D011110:Polymorphism, Genetic; D011148:Pongo pygmaeus; D011323:Primates / Q000235:genetics* / Q000276:immunology; D012452:Saguinus; D012689:Sequence Homology, Nucleic Acid
D018076:DNA, Complementary