The ultrastructural localization of factor VIII-antigen in human platelets, megakaryocytes and endothelial cells utilizing a ferritin-labelled antibody.

By means of electron microscopy combined with the use of monospecific anti-factor VIII-antigen (VIIIR:AG) antibodies conjugated to ferritin, the subcellular localization of VIIR:AG in platelets, megakaryocytes and in endothelial cells has been established. The reported results suggest the possibility that the megakaryocyte is able to synthesize VIIIR:AG and also to secrete it by means of a microcanalicular system similar to that present in the endothelial cell. Platelets may derive their VIIIR:AG content partly from the megakaryocyte and partly from the plasma.