Neither normal nor diseased placentas contain lymphatic vessels

Background

Scant data on placental lymphatic vessels have pointed to the absence of lymphatic circulation. A recent study on mesenchymal dysplasia (MD), however, has identified pathologic lymphangiogenesis using the D2-40 lymphatic marker. These conflicting data have prompted us to investigate whether lymphatic vessels are present in normal developing placentas and in placental disorders characterized by cistern formation.

Design

Seventeen human placentas without significant pathological abnormality ranging from 12 to 39 weeks of gestational age were studied. Cisternal placental disorders were represented by mesenchymal dysplasia (n = 1), partial hydatitiform mole (n = 2), spontaneous abortion (n = 3) and complete hydatiform mole (n = 2). To identify lymphatic vessels, we used lymphatic endothelial markers Prox-1 and D2-40. The pan-endothelial marker CD31 was used to highlight overall placental vasculature and to determine if the lining cells of cisterns were of endothelial origin. Lymphatic marker positivity was assessed in maternal (decidual) as well as in fetal (chorionic villous) vasculature.

Results

No staining with Prox-1 or D2-40 was identified in fetal vessels in developing or term placentas, or in selected cisternal placental disorders, although both markers highlighted a number of thin-walled decidual vessels. Cistern lining cells were negative for Prox-1, D2-40 and CD31. D2-40 consistently marked stromal cells in chorionic villi and highlighted perivascular/pericellular extracellular matrix.

Conclusion

We established that no lymphatic vasculature is present in the chorionic villi during development, at term or in selected edematous placental disorders. The cisternal lining cells are not endothelial cells; most likely they are of stromal cell origin. Lymphangiogenesis is a part of decidual vascular remodeling during gestation.