Does COVID cause our immune system to age prematurely?

Studies show that repeated SARS-CoV-2 infections can cause premature aging of human immune systems

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In a recent update, Ontario public health officials noted emerging evidence that SARS-CoV-2 may cause “immune dysregulation,” a vague term used when the immune system does not behave normally.

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White blood cell counts can be off, immune cells don’t work properly, and inflammation is higher than it should be. “In short, COVID-19 causes permanent and possibly permanent changes in the immune cells of some people, but not all,” said Dawn Bowdish, an immunologist at McMaster University.

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Research has shown that T cells, cells that help produce antibodies and kill infected cells, are particularly vulnerable, and that repeated infections with SARS-CoV-2 may cause premature aging of human immune systems.

The scale is not yet clear. However, “the potential increase in acquired and impaired immunity in the Ontario population could have a significant impact on the incidence and associated burdens of infectious diseases … and other conditions in the long term,” says the Ontario Public Health Brief.

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The concern is that people won’t be able to catch future bugs and pathogens like the flu, or that unstable immune systems could lead to an increase in diabetes and other autoimmune diseases.

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Public Health Ontario said the experts best suited to talk about the issue were tied up in pandemic-related cases and could not be processed. But the possibility that some people’s immune systems are compromised “underscores that getting repeated infections with this thing is not a good thing,” said Kashif Pirzada, an emergency room doctor in Toronto.

When Bowdish first saw a blood sample from someone hospitalized with SARS-CoV-2, he sensed that immune imbalance, a key feature of prolonged COVID, might be the problem. “We tried to understand why some people die in the ICU and others don’t,” Bowdish said. The blood “doesn’t look like human blood anymore.” Their white blood cells were unrecognizable compared to healthy donors.”

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His team has since published a small study showing abnormal white blood cell counts and high inflammation even in asymptomatic and mild “recoveries,” but the problem is more pronounced in people with severe cases of COVID.

“We know that this virus causes a whole bunch of T-cells to die, and we don’t know how, and then it causes white blood cell damage, at least in some people. do after that infection,” said Bowdish, Canada Research Chair in Aging and Immunity. In some cases, the blood cells never fully recover “and appear to trigger autoimmune reactions,” where the body’s immune system attacks its own tissues.

A recent study published in the journal Nature found lower numbers of “naive” T and B cells (antibody-producing cells) in people with COVID.

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T cells have a life cycle, Pirzada said. Naive cells are cells that have not responded to infection. “Once a T cell commits to respond to one thing, it can’t respond to anything else,” Bowdish explained. “As we get older, more of them tend to respond to infections or other things we might be exposed to, and fewer are able to respond to new threats.”

Their decrease is a sign of “immune aging”. We have some flexibility to make even simpler cells, Bowdish said, “but not infinite possibility.”

It doesn’t look like human blood anymore

He doesn’t want to worry too much. “I hope most people will be fine.” It’s also not clear what’s playing.

One theory is that SARS-CoV-2 hyperactivates T cells, and in severe cases, those overactive cells can cause chronic, heightened inflammation, which is responsible for much of the damage to the body, said T-cell researcher Anthony Leonardi.

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A group in Boston reported in a preprint in June that people with long-term COVID have persistent particles of a post-diagnostic protein in their blood that can be a reservoir of infection for up to a year. .

“It’s possible that SARS-CoV-2 can stay in the body and cause immune changes,” Leonardi said.

Others reported that even mildly infected people showed signs of T-cell “fatigue” and that people with multiple COVID infections had “weaker immune memory” against SARS-CoV-2, Leonardi said, after re-infection. “It was like their T cells were giving up the ghost.”

Vaccines and boosters continue to reduce the risk of severe infections. “Once a vaccine or a virus has acquired T cells, theoretically they should be expanded and activated after they have been boosted,” Bowdish said.

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The test showed that most people of kills the virus, and current vaccines “induce robust T-cell responses that contribute to remarkable protection against hospitalization or death.”

But if people lose the rogue cells, they may be less likely to respond to other viruses or infections, “so that’s a major concern,” Bowdish said.

It is not clear whether the damaged T cells are causing more inflammation, but persistent inflammation is not good. People are more likely to have heart disease or stroke.

It is not clear whether the lack of immune cells measured in the blood means that there are fewer of them or that they have gone elsewhere in the body. “We have a lot to learn,” Tanya Watts, an immunologist at the University of Toronto, said in an email.

“However, I agree with the school of thought that because of the long-term risk of COVID and the evidence of long-term effects, it is better to avoid this infection.”

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