IMMUNOLOCALIZATION OF THE INDUCIBLE NITRIC-OXIDE SYNTHASE ISOFORM IN HUMAN FETAL MEMBRANES

PROBLEM: Nitric oxide (NO) synthesized by fetal membranes may protect the fetus from maternal infection or immune challenge or have a tocoly tic effect on myometrium. The sites of synthesis and enzymes responsib le for NO production in human fetal membranes remain unidentified. MET HOD OF STUDY: Fetal membranes were obtained from four groups of patien ts: term (>37 weeks gestation) or preterm (<37 weeks gestation), both either in labor or not in labor. Frozen sections of membrane rolls wer e immunostained for inducible (iNOS) and endothelial (eNOS) nitric oxi de synthase isoforms and the monocyte/macrophage marker CD14. RESULTS: Positive iNOS immunostaining was found in fibroblasts of amnionic and chorionic mesenchyme and in decidual macrophages identified by CD14 f rom all four groups of tissues. No iNOS immunostaining was seen in amn ion epithelium or chorion trophoblast. Very intense iNOS staining was seen with evidence of monocyte/macrophage invasion of membranes, eNOS immunostaining was only found in decidual vascular endothelium. CONCLU SIONS: Constitutive expression of iNOS in decidual macrophages and fet al membrane fibroblasts may form an immune barrier against maternal in sult. In chorioamnionitis, macrophage recruitment and NO expression ma y be part of the maternal immune response.