Severe coronavirus disease 2019 (COVID-19) is associated with a thromboinflammatory condition, which occurs as a result of an overactive immune system. New research in the US and China. investigated how autoantibodies can mediate NETs during COVID-19 infection. Extensive damage to the body from neutrophilic extracellular traps (NET) after infection can contribute to thromboinflammatory and symptoms experienced by COVID-19 ‘long carriers’.
These data reveal high levels of anti-NET antibodies in individuals hospitalized with COVID-19, where they are likely to impair NET clearance and thus potentiate thromboinflamma-mediated SARS-CoV-2. “
The study ‘Autoantibodies stabilize extracellular neutrophil traps in COVID-19’ is available as an overprint on medRxiv* server, while the article is being reviewed.
Increased levels of anti-NET IgG and IgM antibodies in severe COVID-19
The researchers used an enzyme-linked immunosorbent assay (ELISA) to measure antibodies to NET IgG and IgM from blood serum donated from 171 patients hospitalized with COVID-19 along with 48 healthy controls. Controls included 40 women and eight men with an average age of 38 years. People were excluded from the study if they had an autoimmune disease, an active infection, or pregnancy.
The team observed higher levels of anti-NET IgG and IgM in patients with COVID-19 than control groups. About 39% of patients had high anti-NET IgG activity, and 50% showed elevated anti-NET IgM activity. There was a strong correlation between the existence of anti-NET IgG and anti-NET IgM.
Using immunofluorescence microscopy, the team assessed anti-NET activity and found antibodies in NET chains. A positive correlation was found between circulating markers of NET release and anti-NET IgG and IgM.
Anti-NET activity associated with serious illness
A positive correlation was observed between anti-NET IgG and IgM and D-dimers, absolute neutrophil count and platelet count. Likewise, there was a negative correlation with the SpO2 / FiO2 ratio and anti-NET IgG and IgM.
Serum samples from patients with mechanical ventilation showed higher levels of anti-NET IgG and IgM, suggesting that they were associated with impaired respiratory status.
Detection of anti-NET IgG / IgM in the sera of patients with COVID-19. A, Schematic illustration of anti-NET ELISA (created on BioRender.com). BC, Anti-NET IgG, and IgM were measured in sera from 171 hospitalized COVID-19 patients and 48 healthy controls. Mann-Whitney test compared levels of anti-NET IgG and IgM at an optical density of 450 nm (OD); **** p <0.0001. Dashed lines indicate a threshold set to 2 standard deviations above the control center. D, control neutrophils were stimulated with PMA to generate NETs. The fixed NETs were then incubated with COVID-19 serum with high anti-NET antibodies or healthy control serum; scale = 100 microns.
Autoantibodies reduce the ability of serum DNases to clear NET
The next step was to assess the role of autoantibodies in NET degradation. They measured IgG levels in four patients with COVID-19 who had high anti-NET IgG and then tested them with serum from healthy controls. The results showed that high levels of IgG prevent NET degradation.
Given the weakened oxygen intake, increased risk of severe disease and damage to NET degradation, researchers suggest that autoantibodies may play a significant role in long-term damage from people who still have long-term COVID.
It is possible that these anti-NET antibodies are important orchestrators of the imbalance between NET production and clearance that prolongs thromboinflammatory infection COVID-19, ”the research team concluded.
* Important notice
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be considered definitive, guide clinical practice / health-related behavior, or treat it as established information.