Various pathways have been proposed to be linked to the production of
soluble pathogenic factors by the placenta. These include deficient haeme
oxygenase expression, placental hypoxia, genetic factors, autoantibodies
against the angiotensin receptor, oxidative stress, inflammation, altered naturalkillercellsignalling,and,morerecently,deficientcatechol-O-methyl
transferase.4While there is compelling evidence in animal studies demonstrating
an important role for these upstream pathways, the underlying
events that induce placental disease activating the cascade of placental
damage and anti-angiogenic factor production remainun known in humans.