A NEW VARIANT OF INTERACTION BETWEEN PHOSPHOLIPID ANTIBODIES AND THE PROTEIN-C SYSTEM

The influence of 38 IgG fractions with either cardiolipin antibodies o nly (CLa) or both CLa and lupus anticoagulant activity (LA) on the res ponse to activated protein C (APC) and on the snake venom activation o f protein C were investigated. Five of eight IgG fractions with LA act ivity showed a tendency to reduce the effect of APC in the aPTT method and to simulate the APC-resistance phenomenon. This effect was not ob served in IgG fractions without LA activity. The addition of IgG fract ions did not decrease enzymatic activation of protein C in normal plas ma. No correlation was found between sample protein C activity and CLa level or the extent of clotting time prolongation. These observations suggested that acquired resistance to APC in the presence of some typ es of phospholipid antibodies may be a cause of thrombophilia in such patients.