IgM anti-ACE2 autoantibodies in severe COVID-19 activate complement and perturb vascular endothelial function.


The study was done in an opportunity sample of 118 COVID-19 inpatients. Autoantibodies recognizing ACE2 were detected by ELISA. Binding properties of anti-ACE2 IgM from patients were analyzed via biolayer interferometry. The effects of anti-ACE2 IgM on complement activation and endothelial function were demonstrated in a tissue-engineered pulmonary microvessel model.

Anti-ACE2 IgM (but not IgG) were associated with severe COVID-19, found in 18/66 (27.2%) patients with severe disease compared to 2/52 (3.8%) of patients with moderate disease (OR 9.38, 95% CI 2.38-42.0; p=0.0009, Fisher's exact test). Anti-ACE2 IgM were rare (2/50) in non-COVID-19 ventilated patients with ARDS. Unexpectedly, ACE2-reactive IgM in COVID-19 do not undergo class-switching to IgG, and have apparent KD values of 5.6-21.7nM, indicating that they are T-independent. Anti-ACE2 IgM activated complement and initiated complement-binding and functional changes in endothelial cells in microvessels, suggesting that they contribute to the angiocentric pathology of COVID-19.

Our results identify anti-ACE2 IgM as a mechanism-based biomarker strongly associated with severe clinical outcomes in SARS-CoV-2 infection, which has therapeutic implications. We anticipate that additional IgM responses may identify other COVID-19 subgroups with severe disease, and potentially other serious pandemic illnesses.

COVID-19 is a global pandemic caused by the novel coronavirus SARS-CoV-2. Some clinical features of severe COVID-19 represent blood vessel damage induced by activation of host immune responses, initiated by the virus. We hypothesized that autoantibodies against angiotensin converting enzyme-2 (ACE2), the SARS-CoV-2 receptor expressed on vascular endothelium, are generated during COVID-19, and are of mechanistic importance.

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