In vivo inhibition of antiphospholipid antibody-induced pathogenicity utilizing the antigenic target peptide domain I of beta2-glycoprotein I: proof of concept.
OBJECTIVE
In the antiphospholipid syndrome (APS), the immunodominant epitope for the majority of circulating pathogenic antiphospholipid antibodies (aPLs) is the N-terminal domain I (DI) of beta(2)-glycoprotein I. We have previously shown that recombinant DI inhibits the binding of aPLs in fluid phase to immobilized native antigen, and that this inhibition is greater with the DI(D8S/D9G) mutant and absent with the DI(R39S) mutant. Hence, we hypothesized that DI and DI(D8S/D9G) would inhibit aPL-induced pathogenicity in vivo.


METHODS
C57BL/6 mice (n = 5, each group) were injected with purified IgG derived from APS patients (IgG-APS, 500 microg) or IgG from normal healthy serum (IgG-NHS) and either recombinant DI, DI(R39S), DI(D8S/D9G), or an irrelevant control peptide (at 10-40 microg). Outcome variables measured were femoral vein thrombus dynamics in treated and control groups following standardized vessel injury, expression of vascular cell adhesion molecule-1 (VCAM-1) on the aortic endothelial surface, and tissue factor (TF) activity in murine macrophages.


RESULTS
IgG-APS significantly increased thrombus size as compared with IgG-NHS. The IgG-APS thrombus enhancement effect was abolished in mice pretreated with recombinant DI (P <or= 0.0001) and DI(D8S/D9G) (P <or= 0.0001), but not in those treated with DI(R39S) or control peptide. This inhibitory effect by DI was dose-dependent, and at lower doses DI(D8S/D9G) was a more potent inhibitor of thrombosis than wild-type DI (P <or= 0.01). DI also inhibited IgG-APS induction of VCAM-1 on the aortic endothelial surface and TF production by murine macrophages.


CONCLUSIONS
Our findings in this proof-of-concept study support the development of recombinant DI or the novel variant DI(D8S/D9G) as a potential future therapeutic agent for APS.
Ioannou
Y
Y
Centre for Rheumatology Research, Windeyer Building, University College London, London, UK. j.ioannou@ich.ucl.ac.uk
Romay-Penabad
Z
Z
Pericleous
C
C
Giles
I
I
Papalardo
E
E
Vargas
G
G
Shilagard
T
T
Latchman
D S
DS
Isenberg
D A
DA
Rahman
A
A
Pierangeli
S
S
D000818:Animals; D017152:Antibodies, Antiphospholipid / Q000276:immunology* / Q000502:physiology; D004797:Enzyme-Linked Immunosorbent Assay; D017737:Macrophages, Peritoneal / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D013925:Thromboplastin / Q000378:metabolism; D053482:beta 2-Glycoprotein I / Q000737:chemistry / Q000378:metabolism*
D017152:Antibodies, Antiphospholipid; D053482:beta 2-Glycoprotein I; D013925:Thromboplastin