Plasmin immunization preferentially induces potentially prothrombotic IgG anticardiolipin antibodies in MRL/MpJ mice.
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 IgG antiplasmin, IgG aCL, and IgG anti-beta(2)-glycoprotein I (anti-beta(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 IgG anti-beta(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 beta(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, and 2 of 10 inhibited inactivation of FXa by antithrombin III.


CONCLUSIONS
Plasmin immunization leads to production of IgG antiplasmin, aCL, and anti-beta(2)GPI in MRL/MpJ mice, but leads to production of only IgG antiplasmin in BALB/cJ mice. IgG mAb generated from plasmin-immunized MRL/MpJ mice bind to various antigens and exhibit procoagulant activity in vitro. These results suggest that plasmin may drive potentially prothrombotic aCL in genetically susceptible individuals.
University of California, Los Angeles, Division of Pediatric Allergy, Immunology and Rheumatology, Los Angeles, CA 90095, USA. kaleoe@yahoo.com
Kaleo
K
Ede
Kwan-Ki
KK
Hwang
Chen-Ching
CC
Wu
Meifang
M
Wu
Yao-Hsu
YH
Yang
Wei-Shiang
WS
Lin
Daniel
D
Chien
Pei-Chih
PC
Chen
Betty P
BP
Tsao
Deborah K
DK
McCurdy
Pojen P
PP
Chen
D000818:Animals; D017153:Antibodies, Anticardiolipin / Q000378:metabolism*; D016736:Antiphospholipid Syndrome / Q000276:immunology*; D004195:Disease Models, Animal; D005170:Factor X / Q000378:metabolism; D005260:Female; D005341:Fibrinolysin / Q000276:immunology*; D005620:Freund's Adjuvant / Q000276:immunology*; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism*; D008180:Lupus Erythematosus, Systemic / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D019463:Mice, Inbred MRL lpr; D053482:beta 2-Glycoprotein I / Q000276:immunology
D017153:Antibodies, Anticardiolipin; D007074:Immunoglobulin G; D053482:beta 2-Glycoprotein I; D005170:Factor X; D005620:Freund's Adjuvant; D005341:Fibrinolysin