Long Covid caused by body attacking itself after recovery, scientists believe

Harmful antibodies that attack the body’s own tissue may be associated with the condition

Symptoms of long Covid include fatigue, shortness of breath and difficulty sleeping. Alamy

Lingering symptoms from the Covid-19 infection – known as long Covid – are thought to affect as many as 100 million people across the globe.

The number is expected to rise as more people become infected, yet the causes of what can be a debilitating condition – leaving some people unable to walk or to continue with their jobs – have yet to be fully determined.

Long Covid can involve a variety of symptoms, including shortness of breath, memory and concentration problems, fatigue, chest pain and insomnia.

New research from scientists in the US and Germany indicates that autoantibodies, which are harmful antibodies that attack the body’s own tissue, may be associated with long Covid.

The study found that autoantibodies can persist for months in people who have been infected with the coronavirus, and that there are differences between men and women in their types and quantity.

The findings have been published at a time when variation in the susceptibility of men and women to infection by Sars-CoV-2 remains “poorly understood”, according to scientists.

What are autoantibodies and what's their connection to long Covid?

Autoantibodies are antibodies that mistakenly target and react with a person's own tissue and organs. Autoimmune diseases such as coeliac disease and rheumatoid arthritis are caused by such autoantibodies.

The role of autoantibodies in long Covid was identified earlier in the pandemic.

Last July, UK Imperial College London scientists found a pattern of rogue antibodies in the blood of a small number of people with long Covid symptoms.

Autoantibodies are also thought to be involved with acute Covid-19.

In September, a study reported by the US National Institutes of Health found that autoantibodies were present in around half of people in hospital with Covid-19.

Another study that month, also reported by the NIH, estimated that autoantibodies may be responsible for about one in five deaths after infection with the coronavirus.

There is no clear relationship between how ill a person is when they get Covid, according to the National Health Service –the UK's publicly funded healthcare system – or how likely they are to develop long Covid.

What did the latest study find?

Researchers have compared the blood of people who previously had Covid-19 with blood samples collected before the pandemic.

All the samples from people who had been infected with the coronavirus showed increased levels of autoantibodies, according to the researchers.

They found autoantibodies in the blood of individuals up to six months after their infection. This is thought to be the first research to detect autoantibodies for this length of time after a coronavirus infection.

These autoantibodies could, the researchers think, be part of the reason some people have symptoms that last many months after their initial infection.

They also found differences between men and women in autoantibody production. Women tend to be affected more often than men by autoimmune disorders, which may make it seem likely that women would have greater autoantibody production after Covid-19 infection.

However, the researchers found that men showed a “broader AAB [autoantibody] response” than women, a result they described as “apparently paradoxical”.

Why are the findings less surprising than they appear?

Researchers said the pattern in which men showed a broader autoantibody production than women tied in with patterns of disease with Covid-19.

While men and women are about as likely to be infected with the coronavirus, men tend to have worse outcomes, including being more likely to die.

Tying in with this, other chemical indicators of inflammation in men with Covid-19 are usually higher than those in women with the disease.

However, the researchers, who are from Cedars-Sinai Medical Centre in Los Angeles and Oncimmune, an immune system diagnostics company in Dortmund, Germany, also found that women tended to have stronger autoantibody production than men during asymptomatic infections.

Are autoantibodies really important in long Covid?

While the new study highlights the persistence of autoantibodies, it does not provide evidence that they cause long Covid.

Dr Andrew Freedman, an infectious diseases specialist at Cardiff University in the UK, said it was “well recognised” that infections could trigger autoantibody production, but usually this would not be associated with any clinical symptoms.

“However, infection can occasionally trigger the onset of autoimmune diseases, such as rheumatoid arthritis or systemic lupus, in those with a genetic predisposition,” he said.

More studies are needed, he said, to determine the full significance of the study’s findings in relation to Covid-19 and the post-Covid illness that some patients experience.

Another recent piece of research, by scientists at Stellenbosch University in South Africa, may offer further clues about long Covid. It highlighted the significant levels of microclots, or tiny clumps, in the blood of people with severe Covid-19 or long Covid.

These and other clotting-related substances in the blood could, the researchers said, prevent the body’s cells from getting enough oxygen, which could explain the symptoms of long Covid.

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