A 1 siI R A C T I lemophilia B can l)e divided into at least two miuitant forms (lifferelit from the n1ild, moderate, and severe categories l)reviously (lescribe(l. Tn about 90% of hemiophilia B patients.

A partially purified preparation of canine antihemophilic factor was obtained utilizing amino acids as precipitating agents. This AHF preparation was used as the antigen in an immunologic investigation of canine hemophilia. Plasma from rabbits immunized with this preparation contained antibodies which inhibited the coagulation of normal canine plasma. The immune rabbit plasma inhibited AHF activity but had no measurable effect on any other procoagulant. Neither canine hemophilic plasma nor fractions prepared from canine hemophilic plasma contained an antigen capable of neutralizing the inhibitor (no cross-reacting material). The inhibitor titer was inversely proportional to the amount of added AHF in the form of a fraction of normal canine plasma. The inhibitor cross-reacted with human plasma AHF, but not with porcine, bovine, or rabbit AHF. The results of these studies are interpreted as providing further evidence that hemophilia, specifically canine hemophilia, is due to the failure of production of the antihemophilic factor.

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