Migration inhibition factor and the blood clotting system: effects of defibrination, heparin and thrombin.

Heparin is not suitable as an anticoagulant in the leucocyte migration test used to demonostrate the presence of migration inhibition factor (MIF) due to a rapid disappearance of the response after even a short storage of the blood. The use of defibrinated blood is highly recommended and defibrinated blood can be stored for at least 90 min without any diminution of the response. The change in response when using heparinized blood is not due to any direct effect of heparin, because heparin has no effect when added to defibrinated blood. However, heparin, added together with thrombin, is capable of abolishing the MIF effect completely. The basis for this phenomenon is most probably the binding of the heparin-antithrombin cofactor (AT III) to a complex with heparin and thrombin. The activity of MIF requires the presence of AT III, its esterase-inhibiting activity probably being crucial, in order to express MIF activity on macrophages. This mechanism forms a link between certain cellular immune reactions and the blood-clotting system.