Distribution of fibrillin-containing microfibrils and elastin in human fetal membranes: a novel molecular basis for membrane elasticity.

OBJECTIVES

The aim of this study was to determine the distribution of the elastic fiber components, elastin and the extensible fibrillin-containing microfibrils, in human fetal membranes, to understand the possible molecular basis of the membrane elasticity.

STUDY DESIGN

Multiple fetal membrane specimens were obtained immediately after 10 normal vaginal deliveries at term. The distribution of elastin and fibrillin-containing microfibrils was studied by histochemical, immunohistochemical, immunofluorescence, and electron microscopic techniques.

RESULTS

We failed to detect elastin in the fetal membranes with any of the applied techniques. However, fibrillin-containing microfibrils formed abundant longitudinal bundles that were primarily found in the fibroblast and reticular layers. The orientation of these bundles was parallel to direction of membrane stretch. They also formed bundles that extended from the amniotic, chorionic, and decidual basement membranes to the adjacent tissues. The fibrillin-containing microfibrils were also identified in the compact layer and in intercellular spaces of the trophoblasts but not in the spongy layer.

CONCLUSIONS

We suggest that, in the absence of elastin, the structural organization and the extensibility of the fibrillin-containing microfibrils may represent a novel molecular basis for the elastic properties of the fetal membranes and contribute to their strength.