Is COVID prematurely aging our immune system?

Repeated SARS-CoV-2 infections could prematurely age the human immune system, research suggests

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

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White blood cell count may be off, immune cells are not working as they should, inflammation is higher than it should be. “In short, COVID-19 causes long-lasting 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 suggests that T cells, the cells that help produce antibodies and kill infected cells, are taking a particular hit, and that repeated SARS-CoV-2 infections could prematurely age the human immune system.

The scale is not yet clear. However, “a potential increase in weakened acquired immunity in the Ontario population could have a significant impact on the incidence and associated burden of infectious diseases…and other longer-term conditions,” reads the abstract. evidence from Public Health Ontario.

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The worry is that people will be less able to hold off future insects and pathogens like the flu, or that unstable immune systems could lead to a rise in diabetes and other autoimmune diseases.

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Public Health Ontario said its experts best placed to speak on the issue were busy with pandemic-related work and unavailable to elaborate. But the prospect of imbalanced immune systems in some people “underscores that having repeated infections of this thing is probably not a good thing,” said Toronto emergency physician Kashif Pirzada.

Bowdish sensed that immune imbalance, a key feature of long COVID, might be a problem the first time she examined a blood sample from someone hospitalized with SARS-CoV-2. “We were trying to figure out why some people die in intensive care and some don’t,” Bowdish said. The blood “no longer looked like human blood. 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 elevated inflammation even in asymptomatic and mild “recoveries”, although the problem is much more pronounced in people with severe cases of COVID.

“We learned that this virus, and we can’t tell you how, causes a whole bunch of T-cells to die and then seems, at least in some people, to damage the white blood cells that they make after this infection,” said Bowdish, Canada Research Chair in Aging and Immunity.In some cases, blood cells never fully recover “and seem to generate autoimmune reactions,” where the body’s immune system attacks its own tissues.

A recent study published in Nature found lower numbers of “naïve” T and B cells (cells that produce antibodies) in people with COVID.

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T cells have a life cycle, Pirzada said. Naive cells are those that have not yet responded to an infection. “Once a T cell is committed to responding to one thing, it can no longer respond to anything else,” Bowdish explained. “As we get older, more and more of them are engaged in responding to infections, or whatever else we might be exposed to, and fewer and fewer are available to respond to new threats. .”

Having less is a sign of “immune aging.” We have some resilience to create more naïve cells, Bowdish said, “but not an indefinite capacity.”

Didn’t look like human blood anymore

She doesn’t want to sound too alarmist. “Many, hopefully most people, will be fine.” What is at stake is also not entirely clear.

One theory is that SARS-CoV-2 overactivates T cells, and in severe cases these overzealous cells can cause chronic, elevated inflammation that is responsible for much of the damage to the body, the researcher said. on T cells Anthony Leonardi.

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A Boston group reported in preprint in June that people with long COVID have lingering bits of spike protein — the protein that nails the virus’ exterior — in their blood for up to a year, after diagnosis, which could be a reservoir of infection.

“It could be that SARS-CoV-2 remains in the body and causes immune alterations,” Leonardi said.

Others have reported that people with even mild infections show signs of T cell “exhaustion” and that people with multiple COVID infections have “poorer immune memory against SARS-CoV-2” , Leonardi said, making it easier to get reinfected. “It was almost as if their T-cells were dying.”

Vaccines and boosters further reduce the risk of serious infections. “Once you have T cells committed to the vaccine or the virus, in theory those should be expanded and activated once you’re boosted,” Bowdish said.

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A review found that most people do eradicate the virus, and that current vaccines “elicit robust T cell responses that likely contribute to remarkable protection against hospitalization or death.”

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

It’s not clear if damaged T cells produce more inflammation, but persistent inflammation is not good. People are more likely to develop cardiovascular problems or strokes.

It’s also unclear whether a lack of immune cells measured in the blood means there are fewer of them or that they have gone elsewhere in the body. “Much remains to be learned,” University of Toronto immunologist Tania Watts said in an email.

“However, I agree with the school of thought that it is best to avoid this infection, due to the long COVID risks and evidence of long-lasting effects.”

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