Autoimmune antibody (IgG Kansas) against the fibrin stabilizing factor (factor XIII) system

Serum from a patient who died from massive hemorrhage within 4 months after onset of an acquired bleeding disorder at age 85 contained a potent inhibitor of fibrin stabilization. Other parameters of coagulation and fibrinolysis and his bleeding time were within normal limits. The inhibitor was shown to be an IgG with kappa light chains (IgG Kansas); its specific target was the factor XIII system itself. Although IgG Kansas combined with the virgin [ab] form of the zymogen, it did not block the thrombin-catalyzed conversion to [a'b]. However, IgG Kansas prevented the subsequent Ca2+-mediated activation of [a'b] to a + b, where a denotes the catalytically competent factor XIIIa species. IgG Kansas, in contrast to a previously studied autoimmune antibody from a similar bleeding disorder (IgG Warsaw), could also inhibit the transamidating activity of the preactivated a enzyme.