title: The role of the maternal immune system in the regulation of human birthweight.
abstract: Human birthweight is subject to stabilizing selection. Large babies are at risk of obstetric complications such as obstructed labour, which endangers both mother and child. Small babies are also at risk with reduced survival. Fetal growth requires remodelling of maternal spiral arteries to provide an adequate maternal blood supply to the placenta. This arterial transformation is achieved by placental trophoblast cells, which invade into the uterine wall. Under-invasion is associated with fetal growth restriction; but if invasion is excessive large babies can result. A growing body of evidence suggests that this process is controlled by interactions between killer-cell immunoglobulin-like receptors (KIRs) expressed on maternal uterine natural killer cells (uNK) and their corresponding human leukocyte antigen-C (HLA-C) ligands on invading trophoblast. Mothers with the KIR AA genotype and a fetus with a paternal HLA-C2 allele tend to have small babies, because this combination inhibits cytokine secretion by uNK. Mothers with the activating KIR2DS1 gene and an HLA-C2 fetus are more likely to have large babies. When KIR2DS1 binds to HLA-C2 this increases secretion of cytokines that enhance trophoblast invasion. We conclude that specific combinations of the highly polymorphic gene systems, KIR and HLA-C, contribute to successful reproduction by maintaining birthweight between two extremes.
authors.affiliation: Department of Pathology and Centre for Trophoblast Research, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK am485@cam.ac.uk.
authors.forename: Ashley
authors.initials: A
authors.lastname: Moffett
authors.affiliation: Department of Pathology and Centre for Trophoblast Research, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK.
authors.forename: Susan E
authors.initials: SE
authors.lastname: Hiby
authors.affiliation: Department of Pathology and Centre for Trophoblast Research, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Sharkey
mesh_terms: D001724:Birth Weight / Q000502:physiology*; D005260:Female; D047109:Fetal Development / Q000502:physiology*; D005838:Genotype; D015236:HLA-C Antigens / Q000378:metabolism; D006801:Humans; D007694:Killer Cells, Natural / Q000502:physiology; D008431:Maternal-Fetal Exchange / Q000276:immunology*; D010920:Placenta / Q000098:blood supply*; D010929:Placentation / Q000502:physiology*; D011247:Pregnancy; D054340:Receptors, KIR / Q000378:metabolism*; D012641:Selection, Genetic; D014327:Trophoblasts / Q000502:physiology*; D014599:Uterus / Q000166:cytology
chemical_list: D015236:HLA-C Antigens; C496212:KIR2DS1 protein, human; D054340:Receptors, KIR
keywords: birthweight; fetal growth restriction; immunology; natural killer cells; placental development; pre-eclampsia