Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.


C6-Deficient Mice Are Protected from the Pathogenic Effects of Antiphospholipid Antibodies.

L. Carrera-Marin,  A., Aguilar-Valenzuela,  R., Romay Penabad,  Z., Papalardo,  E., Pierangeli,  S.

Background:

The pathogenic mechanisms mediated by antiphospholipid (aPL) antibodies are partially understood. Recent studies have demonstrated the complement involvement in the thrombogenic effects of aPL antibodies. Furthermore, inhibitors for the C5 axis can abrogate aPL effects. The complement membrane attack (C5b-9 MAC) complex has been shown to induce tissue factor (TF) expression (procoagulant effect). However whether C5b-9 MAC plays a role in the pathogenesis of thrombosis in Antiphospholipid Syndrome (APS) is unknown.

Objective:

To study the effects of human and murine aPL antibodies on thrombosis in C6 deficient (C6-/-) mice.

Methods:

C6-/- mice and the corresponding wild-type (C6+/+) were injected twice with either a] 500 mg/ml IgG isolated from two patients with APS (IgG-APS1 and IgG-APS2) or with normal IgG (IgG-NHS), b) 100 mg/ml murine anti b2GPI monoclonal antibodies (4G4) or with mouse IgG 1kMPOC-21(MuMoAb) (Sigma Aldrich) as control or c) 500 mg/ml IgM isolated from a patient with APS (IgM-APS3). Seventy two h after the first injection the size of induced thrombi in the femoral vein was determined. TF activity was determined in homogenates of carotids and peritoneal macrophages using a chromogenic assay. TF expression in macrophages was also determined using quantum dot nano crystals and two-photon excitation laser scanning microscopy.

Results:

Thrombus sizes were significantly larger in C6+/+ mice treated with all different IgG-APS and IgM-APS when compared with healthy controls (p<0.001). Similarly, MuMoAb 4G4 shown significantly difference in thrombus size compared with control MuMoAb. Importantly, C6-/- mice treated with IgGs -APS or IgM- APS or MuMoAb 4G4 had smaller thrombi compared to their C6+/+ counterparts (p <0.001) and there were not significant differences among the control groups.

Thrombus size (mm2)

TreatmentsC6+/+ miceC6-/- mice
IgG-NHS544 ± 99383 ± 119
IgG-APS 1*1649 ± 493732 ± 272
IgG-APS 2*1914 ± 386936 ± 514
MuMoAbC419 ± 122416 ± 178
MuMoAb 4G4*1366 ± 332388 ± 111
IgM-NHS334 ± 117393 ± 113
IgM-APS 3*2268 ± 1004356 ± 122
(*) statiscally significant different from their controls and C6-/- mice counterparts.

TF activity in carotids and in peritoneal macrophages in C6-/- mice treated with IgG-APS1 were significantly diminished. Similarly result was obtained in macrophages TF expression.

All mice injected with IgG-APS had medium-high titers of aCL.

TREATMENTS  
 IgG-NHSIgG-APS 1
Tissue FactorC6+/+ miceC6-/- miceC6+/+ miceC6-/- mice
TF activity in carotids (pmoles/mg·ml-1 protein)17.3 ± 0.219.2 ± 1*51.1 ± 5.629.9 ± 1.8
TF activity in peritoneal macrophages (pmoles/mg·ml-1 protein)12.6 ± 4.34.6 ± 1.2*28.5 ± 13.314.8 ± 9.1
TF expression in peritoneal macrophages (AU)16.0 ± 2.13.7 ± 2.7*40.7 ± 18.29.2 ± 8.5
(*) statiscally significant different from their controls and C6-/- mice counterparts.

Conclusions:

These data indicate that the C6 component of the complement system mediates aPL-thrombogenic effects. The data underscore the possibility of complement inhibition as a new therapy for clinical manifestations of APS.

To cite this abstract, please use the following information:
L. Carrera-Marin, A., Aguilar-Valenzuela, R., Romay Penabad, Z., Papalardo, E., Pierangeli, S.; C6-Deficient Mice Are Protected from the Pathogenic Effects of Antiphospholipid Antibodies. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :1361
DOI: 10.1002/art.29127

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