Immunohistochemical Localization of Factor Viii-related Antigen in Human Endothelial Cells

Immunohistochemical localization of factor VIII-related antigen was studied in human tissues obtained at autopsy or renal biopsy, umbilical cord vessels, smears of washed blood cells and cultured human endothelial cells. Factor VIII-related antigen was demonstrated in the vascular intima throughout the body and cells lining the sinusoids of the lymph node, spleen and liver by an indirect immunofluorescent antibody technique. The existence of factor VIII -related antigen was also demonstrated in the cultured endothelial cells derived from umbilical cord veins. Specific granular immunofluorescent stainings were demonstrated in the cytoplasm of cultured endothelial cells. The findings shown by a direct method were similar to those shown by an indirect method. The localization of factor VIII-related antigen was also demonstrated in the intima of umbilical cord veins by the peroxidase-labeled antibody technique Immunofluorescent staining for the HMW component of factor VIII was detected in the vascular intima and cultured endothelial cells. However, the direct fluorescent method using homologous anti-factor VIII antibody did not show immunofluoresecence in the intima of umbilical cord veins or cultured endothelial cells. This finding suggests that VIII:CAg is not localized in the endothelial cells. The postculture media of human endothelial cells contained factor VIII-related antigen (1.2%), Willebrand factor (0.6%) and no factor VIII coagulant activity. These results indicate that factor VIII-related antigen is localized in endothelial cells, but VIII: CAg is probably not present in endothelial cells.