HLA-G and immune tolerance in pregnancy.
Multiple mechanisms underlie the surprising willingness of mothers to tolerate genetically different fetal tissues during pregnancy. Chief among these is the choice of HLA-G, a gene with few alleles, rather than the highly polymorphic HLA-A and -B genes, for expression by the placental cells that interface directly with maternal blood and tissues. Novel aspects of this major histocompatibility complex class Ib gene include alternative splicing to permit production of membrane and soluble isoforms, deletions that dampen responses to interferons, and a shortened cytoplasmic tail that affects expression at the cell surface. Placental cells migrating into the maternal uterus synthesize both membrane and soluble isoforms, which interact with inhibitory receptors on leukocytes such as ILT2 and ILT4. Cytotoxic T lymphocytes either die or reduce production of one of their major coreceptor/activator cell surface molecules, CD8; natural killer cells are immobilized and mononuclear phagocytes are programmed into suppressive modes characterized by high production of anti-inflammatory cytokines. The idea that placental HLA-G proteins facilitate semiallogeneic pregnancy by inhibiting maternal immune responses to foreign (paternal) antigens via these actions on immune cells is now well established, and the postulate that the recombinant counterparts of these proteins may be used as powerful tools for preventing immune rejection of transplanted organs is gaining in popularity.
Hunt
Joan S
JS
Department of Anatomy and Cell Biology, University of Kansas Medical Center, Kansas City, Kansas 66160-7400, USA. jhunt@kumc.edu
Petroff
Margaret G
MG
McIntire
Ramsey H
RH
Ober
Carole
C
D000483:Alleles; D017398:Alternative Splicing; D000818:Animals; D000938:Antigen-Presenting Cells / Q000276:immunology; D001402:B-Lymphocytes / Q000276:immunology; D005260:Female; D005333:Fetus / Q000276:immunology; D015870:Gene Expression; D006680:HLA Antigens / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I / Q000737:chemistry / Q000235:genetics / Q000276:immunology*; D006801:Humans; D007108:Immune Tolerance / Q000276:immunology*; D007694:Killer Cells, Natural / Q000276:immunology; D010586:Phagocytes / Q000276:immunology; D010920:Placenta / Q000737:chemistry / Q000276:immunology; D011247:Pregnancy / Q000276:immunology*; D011971:Receptors, Immunologic; D054346:Receptors, KIR2DL5; D013601:T-Lymphocytes / Q000276:immunology; D014327:Trophoblasts / Q000276:immunology
D006680:HLA Antigens; D059951:HLA-G Antigens; D015395:Histocompatibility Antigens Class I; D011971:Receptors, Immunologic; D054346:Receptors, KIR2DL5