Cytokines and immune balance in preeclampsia : a survey of some immunological variables and methods in the study of preeclampsia
Abstract: Preeclampsia is one of the most feared pregnancy complications, with a risk of maternal and fetal death and with no ideal therapy readily available. The cause of this strictly pregnancyrelated disease is still unknown and is therefore a great challenge to all researchers in the field of pregnancy-related pathophysiology.Today, the dominating theory of the origin of preeclampsia is defective initial placentation with insufficient penetration of the trophoblasts, leading to impaired maternal blood flow through narrow spiral arteries. However, the cause of this defective trophoblast behavior is not known. The maternal immune system has been proposed to have an influence on both the placentation and the subsequent systemic reactions. Therefore, it is very interesting to study the maternal immune system during preeclampsia, in hope of achieving a better understanding of this puzzling disease.Earlier studies have suggested that normal pregnancy requires a shift to a Th2/antiinflammatory type of immunity, at least directed towards the fetus and placenta, while some pregnancy complications, such as preeclampsia, could be due to a skewed Th1/proinflammatory type of immunity. However, the results from earlier studies designed to test the Th1/Th2 hypothesis in preeclampsia have not been consistent. Therefore, the aim of this thesis was to examine if established preeclampsia is associated with increased innate inflammatory responses and a deviation of adaptive responses towards Th1 when compared with normal pregnancy.Enumerations of cytokine-producing cells from peripheral blood did not show any difference in the production of IFN-γ, IL-4, IL-10 and IL-12 between women with preeclampsia and normal pregnancies. However, a decrease in the spontaneously produced levels of IL-5 was detected in cell cultures on peripheral blood mononuclear cells in women with preeclampsia. Furthermore, a decreased production of IL-10 in response to paternal antigens, believed to represent the fetus, was also detected for the preeclamptic women.Serum analysis showed increased levels of the pro-inflammatory mediators IL-6 and IL-8 during preeclampsia. Also, preeclamptic women displayed increased serum levels of the soluble IL-4 receptor, but no difference in the levels of IL-4 compared to normal pregnant women. This was an elusive finding, since the receptor was originally thought to reflect the levels of IL-4, but has recently been shown to have both agonistic and antagonistic properties on the IL-4 levels. Further studies of the local immune responses in the placenta showed no difference in the immunohistochemical staining of IL-4 and TNF-α between women with preeclampsia and women with normal pregnancies. In general, there were no hallmarks of abnormal morphology in the placental sections examined, regardless of diagnosis.In conclusion, the decreased levels of IL-10 in response to paternal antigens and the systemically increased levels of IL-6 and IL-8 suggest a specific decrease in antiinflammatory responses towards fetal antigens, together with a systemic activation of proinflammatory mediators during preeclampsia. Furthermore, the decreased production of IL-5 also indicates, at least partly, decreased Th2 responses in the established preeclampsia.
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