Association of lupus anticoagulant with transient antibodies to prothrombin in a patient with hypoprothrombinemia

Lupus anticoagulant (LA) is an acquired inhibitor usually associated with thrombotic tendency and rarely with haemorrhagic manifestations, except in cases of LA with hypoprothrombinemia. In vitro LA is manifested with a prolongation in the activated partial thromboplastin time. LA is heterogeneous in nature and appears to be phospholipid-dependent. In most of the cases these antibodies recognize protein phospholipid complexes or proteins such as β2 Glycoprotein I (β2GPI) or prothrombin which can be reconfigured on other surfaces (plastic or phospholipids) and can be expressed as a neo-epitope. Antibodies associated with LA may constitute a different entity from antibodies measured with anticardiolipin/antiphospholipid immunoassays. These latter are actually targeted to β2GPI-phospholipid complexes. When antibodies to prothrombin are present, they are usually non-neutralizing, but immune complexes formed induce an accelerated clearance of prothrombin and affected patients may develop hypoprothrombinemia. There is now evidence that antiprothrombin antibodies react with prothrombin bound on phospholipids in the presence of calcium, as well as with prothrombin alone. The occurrence of hypoprothrombinemia associated with LA and deficiencies of factors involved in the intrinsic pathway has been reported in some patients. When these antibodies appear in children they are frequently transitory and are usually associated with infectious diseases. They are typically allo-antibodies and present species specificity. Once the convalescence phase of acute illness has passed, the associated coagulation abnormalities return to normal. Antibodies to prothrombin have been demonstrated using different methods such as crossed immunoelectrophoresis, binding to radiolabelled prothrombin, or by their interference in purified clotting systems. ELISA methods have also been introduced for the evaluation of these antibodies by their binding to prothrombin coated micro-plates. In this study, we report the case of a young patient who developed a transitory lupus anticoagulant activity associated with purpuric manifestations without thrombotic tendency. The patient was thoroughly investigated and the presence of an antibody to prothrombin was demonstrated by its binding to prothrombin coated plates in an ELISA technique.