Plasmin immunization preferentially induces potentially prothrombotic IgG anticardiolipin antibodies in MRL/MpJ mice (original) (raw)

2009, Arthritis & Rheumatism

Objective-To test the hypothesis, utilizing 2 experimental mouse models, that plasmin is an important autoantigen that drives the production of certain IgG-anticardiolipin (aCL) antibodies in patients with the antiphospholipid syndrome. Methods-BALB/cJ and MRL/MpJ mice were immunized with Freund's complete adjuvant in the presence or absence of human plasmin. The mouse sera were analyzed for production of IgGantiplasmin, IgG-aCL, and IgG-anti-β 2-glycoprotein I (anti-β 2 GPI) antibodies. IgG monoclonal antibodies (mAb) were generated from the plasmin-immunized MRL/MpJ mice with high titers of aCL, and these 10 mAb were studied for their binding properties and functional activity in vitro. Results-Plasmin-immunized BALB/cJ mice produced high titers of IgG-antiplasmin only, while plasmin-immunized MRL/MpJ mice produced high titers of IgG-antiplasmin, IgG-aCL, and IgGanti-β 2 GPI. Both strains of mice immunized with the adjuvant alone did not develop IgG-antiplasmin or IgG-aCL. All 10 of the IgG mAb bound to human plasmin and cardiolipin, while 4 of 10 bound to β 2 GPI, 3 of 10 bound to thrombin, and 4 of 10 bound to the activated coagulation factor X (FXa). Functionally, 4 of the 10 IgG mAb inhibited plasmin activity, 1 of 10 hindered inactivation of thrombin by antithrombin III (AT), and 2 of 10 inhibited inactivation of FXa by AT. Conclusion-Plasmin immunization leads to production of the IgG mAb antiplasmin, aCL, and anti-β 2 GPI in MRL/MpJ mice, but leads to production of only IgG-antiplasmin in BALB/cJ mice. IgG mAb generated from the plasmin-immunized MRL/MpJ mice bind to various antigens and exhibit procoagulant activity in vitro. These results suggest that plasmin may drive the potentially prothrombotic activities of aCL in genetically susceptible individuals. The antiphospholipid syndrome (APS) is characterized by clinical manifestations of vascular thrombosis and pregnancy loss associated with the presence of persistently and significantly increased titers of antiphospholipid antibodies (aPL) (1-6). The antigenic specificities of aPL have been the subject of a number of studies, and these studies have shown that aPL represent a heterogeneous group of immunologically and functionally distinct antibodies that recognize