Background/Purpose:

Antiphospholipid syndrome (APS) is a multisystemic autoimmune disease characterized by recurrent thrombotic and adverse obstetric events in the presence of antiphospholipid antibodies (aPL). Compelling data indicate a key role for aPL-mediated induction of tissue factor (TF) expression in monocytes and endothelial cells in the pathogenesis of APS. Recent in-vivo data from our group utlizing low TF producing mice demonstrated the importance of TF in aPL-mediated thrombosis. There is however limited in-vivo data demonstrating the source of TF in the vessel wall in thrombosis resulting from aPL activity.

The aim of this study was to determine the major sources of TF expression in the arterial wall of mice subjected to passive aPL administration.

Methods:

CD1 male mice (n=5 per group) were inoculated with either purified whole IgG from an APS patient (IgG-APS) with high IgG aPL and documented aterial and venous thrombosis or with whole IgG from normal human serum (IgG-NHS). Antibodies were purified from serum using diethylaminoethanol (DEAE) sepharose and adjusted to the appropriate concentration in phosphate buffered saline and any endotoxin present was removed by a commercially available column (Thermo Scientific). Mice were treated with the IgG solutions twice intraperitoneally, the second inoculation given 48 hours after the first, and surgery to measure thrombus dynamics of thrombi induced by a standardized pinch injury to the femoral vein and to collect the aorta was done 72 hours after first inoculation. Staining for TF in the aortic wall was performed by immunohistochemistry using an anti-TF primary antibody, an Alexa-Fluor 586 conjugated secondary antibody and 4′,6-diamidino-2-phenylindole(DAPI) counterstain on formalin fixed and paraffin embedded aorta specimens.

Results:

The mean thrombus size was significantly larger in IgG-APS treated mice (1747.4±362.6 um²) compared to those given IgG-NHS (613.6±127.3um²) (p<0.001). Staining for TF in the aortic wall of IgG-NHS mice revealed minimal staining in the media and moderately more intense staining in the adventitia. In IgG-APS treated mice, there was consistently intense TF staining in the adventitia and moderate staining in the media, noticeably greater than that seen in NHS treated mice.

Conclusion:

In this mouse model, IgG aPL induced significantly larger thrombi than control IgG and was associated with a noticeable increase in adventitial and medial TF, with the adventitia being the major source. Further study is needed to determine the specific cellular sources of TF important in aPL-mediated thrombosis.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/antiphospholipid-antibody-mediated-increase-of-tissue-factor-in-arterial-wall-is-associated-with-increased-thrombus-size-in-a-mouse-model/