In a study from McMaster University, scientists found that blood samples drawn from patients with long COVID who are still suffering from fatigue and shortness of breath after a year show signs of autoimmune disease.
Autoimmune disease occurs when the immune system mistakenly attacks healthy parts of the body, instead of defending the body against disease. It causes conditions such as rheumatoid arthritis and lupus.
This finding offers clues about the nature of long COVID that could ultimately lead to improvements in diagnosing and treating the condition.
In the study, the team examined 106 people who had been diagnosed with COVID-19 between August 2020 and September 2021.
They also included a group of 22 healthy volunteers and a group of 34 people who had experienced a non-COVID respiratory infection as a comparison.
On three occasions—3, 6, and 12 months after they recovered from the infection—patients were asked if they were suffering any shortness of breath, coughing or fatigue (typical symptoms of long COVID).
The researchers tested the samples for particular antibodies. Antibodies are normally produced by the immune system to stick to potentially harmful bacteria or viruses, marking them out for attack by other parts of the immune system.
In this case, the researchers looked for antibodies that target healthy cells and tissues in the body and that are known to contribute to autoimmune diseases.
They found nearly 80% of the COVID-19 patients had two or more of these antibodies in their blood three months and six months after the infection. This fell to 41% after a year.
Most of the healthy volunteers had no sign of these antibodies in their blood and in those who had experienced a non-COVID respiratory infection, levels of these antibodies were comparatively low.
Researchers also found that two specific “autoantibodies” (called U1snRNP and SSb-La autoantibodies), along with other proteins (called cytokines) that cause inflammation, persisted in around 30% of COVID patients a year after infection.
This tended to be among those patients who were also still suffering from fatigue and shortness of breath.
The team says for the majority of the patients in our study, even if they had autoantibodies soon after their infection, this resolved after 12 months.
However, in some patients, autoantibodies persist, and these patients are more likely to continue suffering from symptoms and need medical help.
These results point toward the need to test for signs of autoimmune disease in patients with symptoms of long COVID that last for a year or more.
For more information about COVID, please see recent studies about a drug combo that may help treat COVID-19, and results showing why COVID-19 is severe in some people and mild in others.
The study was conducted by Dr. Manali Mukherjee et al and published in the European Respiratory Journal.
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