ULTRASTRUCTURAL DISTRIBUTION OF ENDOGENOUS IMMUNOGLOBULIN-G IN HUMAN TERM AMNIOCHORION

Maternal immunoglobulin-G (IgG) is known to be transported across the placental syncytiotrophoblast during the period when the human fetus i s incapable of manufacturing these defensive molecules. In this study we investigated the possible role of the amniochorion, that surrounds the amniotic cavity in which the fetus lies, in the transfer of immuno globulin. Endogenous IgG was localised in the amniochorion by confocal immunofluorescence microscopy and by ultrastructural labelling of ult rathin frozen tissue sections using the protein A-gold technique. Immu noreactivity was identified in the extracellular matrix tissues and ne crotic amniotic epithelial cells. Healthy amniotic epithelial cells an d cytotrophoblast cells of the chorion laeve were devoid of endogenous IgG. These results suggest a possible nonspecific paracellular transp ort pathway between cytotrophoblast cells, which may conceivably contr ibute to the acquisition of passive immunity by the fetus, and offer a rational explanation for the presence of small quantities of maternal IgG in the amniotic fluid.