Summary
1. In 2 patients blood coagulation inhibitors have been found. The first patient showed pancytopenia, splenomegaly and increase of macroglobulins in serum, no definite clinical diagnosis could be established. The second patient had a history of thromboembolic diseases, but appeared healthy at the time of investigation.
2. Clotting time, partial thromboplastin time and prothrombin time were prolonged in both patients. All clotting factors were normal if tested in dilution. Plasma and serum of the patients prolonged the partial thromboplastin time and prothrombin time of normal plasma.
3. Using partially purified clotting factors it could be shown that the inhibitors inhibit the activation of prothrombin by prothrombin activator (reaction product of F Xa+ F V+lipid). The velocity of thrombin generation and the amount of thrombin generated was reduced.
4. The inhibitory activity in both cases was present in the macroglobulin peak after gel filtration, slight activity was detected also in the G-peak in case 2. After DEAEchromatography, activity appeared in both cases in those fractions which contain IgM, in case 2 also in the first protein fractions containing only IgG.
5. Inhibitor activity could be reduced in both cases only be incubation with anti-IgM antiserum.
6. It is concluded that the inhibitor in case 1 is IgM and in case 2 IgM-IgG.
