Demonstration of Factor Xiii in Human Megakaryocytes by a Fluorescent Antibody Technique*

Summary This work presents direct evidence for the cytoplasmic location of clotting Factor XI11 in human bone marrow megakaryocytes. This indicates that blood platelets derive Factor XI11 through de novo synthesis rather than through plasmatic transport across the platelet membranes. Evidence from plasma Factor XI11 assays of thrombocytopenic patients indicates that a major source of plasma Factor XI11 can be outside the platelet or megakaryocyte. The possible role of platelet Factor XI11 in the hemostatic process is discussed.