Enhanced expression of the immunoregulator, p43-placental isoferritin, in Down's syndrome placentae and fetal kidneys.

Human placental isoferritin is composed of a 43 kDa subunit and ferritin light chains. It acts as an immunosuppressive cytokine in normal gestation and in some malignant conditions. We investigated p43-placental isoferritin expression at the maternal fetal tissue interface and in fetal kidneys in Down's syndrome (DS) compared with normal control samples. Following termination of mid-gestation pregnancies placental and fetal kidney tissue samples were collected. Immunohistochemical analysis of the specimens was performed using a monoclonal antibody generated against human p43-placental isoferritin protein (CM-H-9 mAb). Expression of p43-placental isoferritin was detected in Hofbauer cells and in the syncytial layer of placental tissue. Significantly higher numbers of positive Hofbauer cells were detected in DS placentae at 17 weeks gestation compared with the controls. The number of immunopositive Hofbauer cells decreased in DS placentae at 20 weeks gestation, 3 weeks later than in controls. In kidneys of fetuses at 17 weeks gestation, p43-placental isoferritin immunoreactivity was confined to the proximal tubules of the nephrons. DS kidneys had higher staining intensities compared with similar gestational age controls. Enhanced expression of p43-placental isoferritin was observed in DS placentae and fetal kidneys. This may explain the increased p43-placental isoferritin levels in the maternal serum of DS gestations.