A Unique Factor XI11 Inhibitor to a Fibrin-Binding Site on Factor XIIIA

An 81-year-old woman, who presented with sudden episodes of spontaneous bleeding, was found to have a specific inhibitor of factor XIII. Her fibrin clots had 70% y y and no a polymer formation, under conditions where normal fibrin was fully cross-linked; the patient’s clots were soluble in urea or monochloroacetic acid. Factor Xll l activity in her plasma was 24%. measured by the dansylcadaverine incorporation assay. When mixed with normal plasma, the patient’s plasma inhibited fibrin cross-linking; however, in mixtures of patient and normal plasma, there was no inhibition of factor Xll l activity when assayed by the incorporation of dansylcadaverine into casein. Thus, this inhibitor was active against fibrin cross-linking but not against ligation of small molecules t o casein. Consequently, gel electrophoresis of reduced, sodium dodecyl sulfate-solubilized fibrin clots was a