Crystalloid inclusion bodies of the endothelial cells in human fetal skin blood vessels and human umbilical cord vessels: A possible relationship to Weibel-Palade bodies?

Crystalloid inclusion bodies (CIB) of the endothelial cells (EC) were investigated in blood vessels of human fetal skin and the umbilical cord by electron- and immunoelectron microscopy. They were found in up to 15% of the investigated EC in various types of vessels. Their sizes ranged from 0.2 μm to 0.6 μm in the largest diameter. Most frequently we observed a laminated pattern of the crystalloid structure with a regular periodicity of dark and light bands. Additionally a honeycomblike pattern was also seen. Measurement of the CIB laminated structure revealed similar dimensions to Weibel-Palade bodies (WPB). In EC of all vessel types we found numerous WPB differing in electron density, shape and size from those of WPB found in adult blood vessels. WPB were found much less frequently in EC with CIB, suggesting that CIB is a precursor of WPB. After incubation with monoclonal antibody against von Willebrand factor (vWf) both WPB and large organelles were labeled. Because of their shape and size the labeled large organelles seemed to represent inadequately preserved CIB. After incubation with anti-lysozyme only the large organelles were labeled. A possible relationship of CIB to WPB is thus suggested. The presence of lysosomal enzymes such as lysozyme suggest that CIB are lysosomal organelle and participate in the uptake of vWf. The crystalloid pattern of CIB may represent an accumulation of a highly condensed form of vWf.