Anti-DNA antibodies cross-reactive with β₂-glycoprotein I induce monocyte tissue factor through the TLR9 pathway

Abstract

Antibodies specific for cardiolipin (CL)-b 2-glycoprotein I (b 2 GPI) are known to induce tissue factor (TF) expression by monocytes and endothelial cells which leads to a prothrombotic state in antiphospholipid syndrome (APS), but the mechanism is not fully elucidated. Previously, we reported that the mouse monoclonal anti-CL-b 2 GPI antibody WB-6 crossreacts with DNA, enters monocytes via binding to cell surface DNA, and induces TF expression. The current study aimed to identify the intracellular signaling pathways involved in this process. The binding of WB-6 to CL-b 2 GPI or DNA, and endocytosis was not prevented by chloroquine, but pre-treatment of the cells with chloroquine significantly suppressed TF expression. TLR9 inhibitory oligodeoxynucleotide also suppressed the WB-6-induced TF expression, suggesting a pivotal role of the TLR9 pathway in TF production. Serum antibodies obtained from a patient with APS accompanying systemic lupus erythematosus (SLE) bound to both CL-b 2 GPI and DNA, and induced TF in normal monocytes. This effect was suppressed by chloroquine, and abolished by removal of the DNA-binding activity. These results suggest that induction of TF expression results from TLR9 activation by DNA which was internalized together with cross-reactive antibodies produced in secondary APS accompanying SLE.

Molecular Mechanisms of “Antiphospholipid Antibodies” and Their Paradoxical Role in the Pathogenesis of “Seronegative APS”

“…Additional studies demonstrated that aPL may also induce the translocation of TLR-7 or TLR-8 from the endoplasmic reticulum to the endosome [93], these effects depend on the uptake of aPL into the endosome, subsequent activation of endosomal NADPH oxidase and generation of superoxide. A pivotal role for TLR-9 pathway in TF production by monocytes was also recently reported [94].…”

Targeting thromboinflammation in antiphospholipid syndrome

“…Finally, ROS production by endosomal NOX-2 may be blocked with ubiquinol or patients with non-APS related thrombosis [36,37]. Purified patient anti-β2GPI IgG increases the TF expression in healthy donor monocytes [38,39]. Macrophages from anti-β2GPI antibody-treated mice also produce significantly more TF mRNA [30].…”

The role of monocytes in thrombotic diseases: a review

“…A study of how WB-6 (a mouse monoclonal anti-β2Gpi antibody) contacts and activates resting-state monocytes showed that monocytes internalizing WB-6 express TF and TNF-α, TNFα stimulates ECs to express ICAM-1 and VCAM-1 (181). Later, another study identified the signaling pathways within cells involved in this process and suggested that the induction of TF expression was the result of the internalization of DNA-activated TLR9 together with cross-reactive antibodies produced by SLE secondary APS (182). It has proved that the β2GPI dimerization domain V(β2GPI-dV) dimerization of β2GPI-dV is sufficient to induce the up-regulation of procoagulant activity of monocytes (183).…”