Tolerance to the foeto-placental 'graft': ten ways to support a child for nine months

Tolerance to the foetal 'allograft' has been extensively studied in the pas t few years, providing interesting new insights. In addition to a potential role for HLA-G, which has been widely discussed, there are hypotheses sugg esting roles for several other molecules or cells: leukemia inhibitory fact or and its receptor; indoleamine 2.3-dioxygenase; the Th1/Th2 balance; supp ressor macrophages; hormones such as progesterone or the placental growth h ormone; CD95 and its ligand; and, as recently proposed, annexin II. Toleran ce of the foetal allograft is probably the consequence of a wide panel of m echanisms that may or may not be pregnancy-specific, that are of major or s econdary importance and that may be interconnected.