Localization of type II phospholipase A2 messenger RNA and immunoactivity in human placenta and fetal membranes.

Although Type II phospholipase A2 (PLA2) immunoactivity has been identified in homogenates of human placenta and fetal membranes, there is a paucity of information concerning the sites of synthesis of this secreted PLA2 isozyme. The aim of this study, therefore, was to establish the cellular localization of Type II PLA2 messenger RNA (mRNA) in human term placental and fetal membranes by in situ hybridization. In addition, the co-localization of immunoreactive Type II PLA2 in gestational tissues was determined, and the effect of labour status and pre-eclampsia on immunolabelling intensity were established. Type II PLA2 mRNA was identified in all tissue sections examined and was localized principally in placental villous vasculature and mesenchymal elements of placenta, chorion and amnion. Within the vasculature, Type II PLA2 mRNA was associated with smooth muscle cells. Immunoreactive Type II PLA2 was identified in the fibroblast and spongy layers of the amnion, the fibroblast and reticular layer of the chorion, and in the mesenchymal core and trophoblasts of placental villi. Immunolabelling staining intensity was greater in placenta and chorion than that observed in amnion, however, staining intensity was unaffected by labour status. Pre-eclampsia was associated with increased immunolabelling for Type II PLA2 in placenta but not fetal membranes. The data obtained clearly established that Type II PLA2 is synthesized by multiple cell types within human gestational tissues and co-localization of Type II PLA2 mRNA and immunoreactive protein has been established. The role of Type II PLA2 in gestational tissue phospholipid metabolism and, in particular, in vascular and mesenchymal elements, has yet to be established. Possible roles for this isozyme may include, the provision of substrate for eicosanoid synthesis, maintaining cell membrane phospholipid asymmetry and prevention of clot formation within the placental vascular bed.