‘Nothing but NET[osis]’: RheumMadness 2022 Anti-NET Antibodies Scouting Report

Editor’s note: RheumMadness is the place for everyone crazy about rheumatology to connect, collaborate, compete and learn together. During RheumMadness, rheumatology concepts represent teams that compete against each other in a tournament, much like basketball teams do in the NCAA’s March Madness tournament. In a series for The Rheumatologist, readers will get a chance to read the scouting reports for each concept team. These reports are written by rheumatology fellows from 13 programs throughout the U.S.

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Region: Cells

Team: Anti-NET Antibodies

Activated neutrophils produce neutrophil extracellular traps (NETs), networks of DNA and proteins via a process called NETosis, to trap and kill pathogens. NETs are implicated in a multitude of autoimmune disease processes and may be involved in thrombophilic disease states, such as antiphospholipid syndrome (APS), cancer and COVID-19 infection.

In the base article for this RheumMadness team, researchers suggest that in primary APS antiphospholipid antibodies engage the neutrophil surface by circumventing normal homeostatic mechanisms to trigger the release of NETs. Patients with APS were found to have higher levels of circulating NETs than healthy controls. Activity of circulating anti-NET antibodies was measured in 76 patients with primary APS, 23 patients with SLE without antiphospholipid antibodies (aPL), 11 patients with a history of unprovoked venous thromboembolism (VTE) without aPL and 44 healthy controls.¹

The researchers found patients with primary APS have markedly elevated levels of circulating anti-NET IgG and IgM antibodies compared with healthy controls. Patients with SLE without positive aPL also had elevated anti-NET IgG and IgM antibodies. Those with a history of unprovoked VTE without aPL had higher levels of IgM anti-NET antibodies than healthy controls. Anti-NET antibody activity in primary APS did not correlate with levels of traditional aPL (e.g., anti-B2GP1 and lupus anticoagulant) and was relatively stable over time. Further, anti-NET antibodies—particularly IgG—impaired the ability of patient sera to degrade NETs, and levels of anti-NET IgM were inversely correlated with complement C4 levels, suggesting activation of the complement cascade. The researchers hypothesized NETs can directly activate complement, which may promote coagulation through effects on tissue factor and platelets. Lastly, both IgG and IgM anti-NET antibodies were associated with clinical manifestations of APS (e.g., unproved venous thrombosis and arterial thrombosis), and high IgG levels were associated with recurrent venous thrombosis.

Overall, high levels of anti-NET antibodies were seen in patients with primary APS and were thought to impair NET clearance and activate the complement cascade, leading to clinical manifestations of APS, including thrombosis. These antibodies may potentially be used to risk-stratify patients with positive aPL antibodies and perhaps be used to determine an indication for primary thrombosis prophylaxis based on thrombotic risk. 

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The Implications

This study identifies potential biomarkers to stratify the risk for primary/secondary autoimmune thrombotic phenomena. Although APS diagnostic criteria are established, appropriate cut-off values for antiphospholipid antibody positivity are debated. In individuals with a clotting history and positive antiphospholipid titers below the APS cut-off values (i.e., <40 units or below the 99th percentile), anti-NET titers and/or NET degradation measurements may serve as additional biomarkers to risk stratify patients who would benefit from anticoagulation. Perhaps individuals without a clotting history, but with anti-NET antibodies, may benefit from prophylactic anticoagulation.

Additionally, the study identifies additional humoral connections to thrombotic phenomena. Thus, B cell therapies, such as rituximab and belimumab, may modulate thrombotic risks in patients with anti-NET antibodies regardless of the presence of antiphospholipid antibodies. Because anti-NET antibody serologies are associated with complement consumption markers, B cell therapies for patients with anti-NET antibodies may ultimately decrease thrombotic risk in diseases mediated by immune complex deposition and complement activation, such as lupus. Alternatively, perhaps anti-NET antibody serologies represent a new pharmacological treatment target.

The NET microenvironment warrants further exploration. Perhaps different antigen-binding sites for anti-NET antibody serologies confer different thrombotic risks. Given that many rheumatic illnesses are associated with increased thrombotic risk, perhaps other autoimmune serologies, such as anti-ds-DNA or anti-CCP, also cross-react with NET antigens to promote thrombotic phenomena. 

Given the evolving understanding of the NET microenvironment as it relates to thrombotic pathology, larger studies are needed to confirm the results of this study and better elucidate other thrombotic associations with anti-NET antibody serologies. If the results of this study are reproducible, we anticipate a future in which clinicians may potentially use commercially available anti-NET antibody assays in combination with anti-phospholipid assays to better understand thrombotic risks. 

2022 Tournament Chances

Since 2004, NET biology has flourished, and we now know NETs contribute to the pathogenesis of multiple autoimmune conditions. This paper examines a further potential implication of NET dysregulation via anti-NET antibodies on thrombosis generation. Additional studies may further elucidate this finding to potentially equip clinicians with a biomarker to assess thrombotic risk among patients.

NETs haven’t been this popular since 1993 when Michael Jordan, a University of North Carolina graduate considered the best basketball player ever, popularized the phrase “nothing but NET[osis].” Just like Jordan, we’re confident our nets will entrap the other teams—including our first-round competitor, Cytokine Networks—and we will prevail.

Shruti Chandramouli, MD, is a second-year rheumatology fellow in the University of North Carolina Rheumatology Fellowship Program.

Christopher Overton, MD, is a second-year rheumatology fellow in the University of North Carolina Rheumatology Fellowship Program. 

Astia Allenzara, MD, is a first-year rheumatology fellow in the University of North Carolina Rheumatology Fellowship Program.

Michael Cunningham, MD, is a first-year rheumatology fellow in the University of North Carolina Rheumatology Fellowship Program.

Luis Palomino, MD, is a first-year rheumatology fellow in the University of North Carolina Rheumatology Fellowship Program.

References

1. Zuo Y, Yalavarthi S, Gockman K, et al. Anti-neutrophil extracellular trap antibodies and impaired neutrophil extracellular trap degradation in antiphospholipid syndrome. Arthritis Rheumatol. 2020 Dec;72(12):2130–2135.

Sources

1. Zuo Y, Yalavarthi S, Gockman K, et al. Anti-neutrophil extracellular trap antibodies and impaired neutrophil extracellular trap degradation in antiphospholipid syndrome. Arthritis Rheumatol. 2020 Dec;72(12):2130–2135.
2. de Bont CM, Stokman MEM, Faas P, et al. Autoantibodies to neutrophil extracellular traps represent a potential serological biomarker in rheumatoid arthritis. J Autoimmun. 2020 Sep;113:102484.
3. He Y, Yang FY, Sun EW. Neutrophil extracellular traps in autoimmune diseases. Chin Med J (Engl). 2018 Jul 5;131(13):1513–1519.
4. Yipp BG, Kubes P. NETosis: How vital is it? Blood. 2013 Oct 17;122(16):2784–2794.