Natural IgM antibodies reduce the prothrombotic potential of post-translationally modified collagen

Introduction: Exposure of atherosclerotic plaque content to blood flow leads to atherothrombosis complications such as myocardial infarction and stroke. The oxidative environment of atherosclerotic plaques promotes the generation of lipid peroxidation products, such as malondialdehyde (MDA), which can modify various pro-coagulatory plaque components like collagen. This modification creates neo-epitopes that are recognized by natural IgM antibodies. Titres of MDA-specific IgM antibodies inversely correlate with cardiovascular disease (CVD) risk, but the mechanisms by which they are protective are not fully understood. We hypothesize that MDA specific IgMs exert their protective effect through direct inhibition of atherothrombosis.

Method: To elucidate this, we in vitro MDA modified collagen and evaluated the ability of natural IgMs to inhibit MDA modified collagen induced coagulation in vitro and in vivo. In vitro, both primary hemostasis (multiplate platelet aggregation, FACS platelet activation, light transmission aggregometry) and secondary hemostasis (fibrin generation assay, thrombin generation assay, thromboelastometry) were assessed. Ex vivo, a flow chamber model was used to assess the effects on fibrin generation and platelet aggregation under arterial shear stress. For in vivo verification a mouse pulmonary thrombosis model was utilized. Finally, results were confirmed patient cohort at risk of atherothrombotic events.

Results: MDA-modified type I collagen and human plaque homogenates activated whole blood clot formation (thromboelastometry), platelet activation (Multiplate) and the coagulation cascade (thrombin generation). These effects were inhibited by addition of LR04, an MDA specific monoclonal IgM, but not an isotype control IgM. Ex vivo, LR04 significantly delayed clot formation on a MDA collagen coated surface in a flow chamber assay compared to isotype control. Similarly, LR04 but not an isotype control protected from mouse pulmonary embolism triggered by injection of MDA collagen. Importantly, high titres of endogenous IgM antibodies with specificity for MDA collagen were associated with significantly increased survival in patients with carotid artery disease.

Conclusion: Taken together, we describe a novel protective mechanism of MDA-specific IgMs through direct inhibition of atherothrombosis via reduction of platelet and coagulation cascade activation.

Publication History

Article published online:
13 February 2025