Plasminogen binding by human amniochorion. A possible factor in premature rupture of membranes.

Forty-six human fresh amniochorion membranes obtained at cesarean section were found to contain from 0 to 5% dead cells in the amniotic epithelial layer by direct counting and spectrophotometric analysis of trypan blue extracts. With the use of a double marker system it was discovered that many of the dead cells failed to bind the DNA-chelating fluorochrome propidium iodide but reacted with fluorescein isothiocyanate-labeled antibodies to human plasminogen. In addition, both fresh and cultured human amniotic epithelial cells that had plasma membranes damaged by either cryogenic shock or cytocentrifugation specifically bound plasminogen from serum, plasma, or amniotic fluid to cytoplasmic structures. Binding did not occur in other control proteins, but plasminogen was bound from very dilute solutions, suggesting specific and tight binding inside the cell. We propose that such plasminogen can be activated to plasmin within the cell by either plasminogen activators or lysosomal proteases and that this sets into motion a progression of events that are potentially damaging for the amniochorion, perhaps being of relevance in the pathophysiology of premature rupture of the membranes in human pregnancy.