Placental cytokines and preeclampsia.
Preeclampsia is a serious and life-threatening pregnancy complication. Reduced uteroplacental perfusion and oxygen tension, impaired trophoblast differentiation and invasion, and altered placental production of immunomodulators and growth factors are all considered to be important aspects in the aetiology of the condition. The placenta expresses a variety of pro and anti-inflammatory cytokines, adipokines and cytokine-like angiogenic growth factors, production of which is altered in preeclampsia, driven (at least in part) by hypoxia. Altered levels of cytokines have been measured in the circulation of women with preeclampsia, although for reasons that are not always apparent much of the data are disturbingly inconsistent. While the placenta undoubtedly makes an important contribution to plasma cytokine levels, production by maternal peripheral blood mononuclear cells (PBMCs) and other tissues is also likely to be significant, although to what extent remains undetermined. Increased placental expression of soluble receptors occurs with preeclampsia, resulting in elevated circulating concentrations which confer impaired angiogenesis, deficient placental vascularisation, increased placental apoptosis and endothelial dysfunction. The extent to which these changes reflect a response to the disorder, as opposed to being a causative factor in the development of maternal disease, is a matter of some debate. Nevertheless, convincing evidence is now accruing that autocrine/paracrine interactions between placental cytokines/growth factors and the maternal endothelium play a central role in the pathogenesis of preeclampsia.