Pregnancy,immunology and evolution

Vertebrate systems of innate and adaptive immunity are more than 400 million years old, whereas mammalian placentation evolved 130 million years ago. Placentation evolved in the context of an immune system and has co-opted immune system cells and molecules. Natural killer (NK) cells are lymphocytes that provide defence against viral infection and also co-operate with trophoblast on the invasive remodeling of maternal vessels that supply the placenta with blood. Controlloing these processes are highly variable NK cell receptors that recognize polymorphic major histocompatibility complex (MHC) class I molecules as their ligands. As a consequence of strong and varying selection pressures, these systems of ligands and receptors evolve rapidly and are inherently unstable; thus they have been lost and reinvented on several occasions during mammalian evolution. The human system of killer cell immunoglobulin-like receptors (KIR) only has counterparts in monkeys and apes, species in which the co-evolution of receptors has been tracked. The emergence and diversification of MHC-C and its cognate KIR in hominids correlates with an increasingly invasive placenta. During human evolution the KIR system has undergone unique, qualitative changes that set it apart from the chimpanzee KIR system. The possible causes of these differences will be discussed.VIDEO LINK: http://sms.cam.ac.uk/media/1400816