Scientists are looking past antibodies in the hunt for viral immunity

Could the ghosts of your previous colds help protect you against COVID-19, even if you’ve never been infected by the new coronavirus spreading across the planet?

Scientists are investigating a poorly understood immune mechanism in the body that they hope efforts can help curb the pandemic.

Currently, people who think they may have had the virus can get a serological test to check for antibodies.

These proteins help fight infection and can prevent them from getting the disease again in the future – but there are signs that they could go away with COVID-19 within weeks.

This leaves the other tool in the body’s toolkit – T lymphocytes – a type of white blood cell responsible for the second part of the immune response.

With not much known yet about how they operate against COVID-19, scientists are running to fill in the gaps in our knowledge.

One hypothesis is that these T cells may help protect humans with a level of cross-immunity against COVID-19 because they “remember” previous infections by other viruses in the same family, four of which cause colds.

“The immune system is complex,” said Andreas Thiel, co-author of a study that looked at the presence of T cells that can respond to the new coronavirus, both among those with confirmed infections and healthy human beings.

The survey, published last week in the journal Nature, found that at least one-third of adults who had never had COVID-19 had these T cells.

“These are probably caused by previous infections with endemic coronaviruses,” Thiel, a professor at the Berlin-Brandenburg Center for Regenerative Therapies, told AFP.

But he warned that much more research was needed to determine whether their presence would necessarily imply immunity.

Virus family

The study followed a study by a team in Singapore published earlier in July in Nature that reached a similar conclusion.

Another study from the United States, published Tuesday in the journal Science, found a number of T cells that respond both to the new virus, SARS-CoV-2, and to the coronaviruses that cause colds.

“This may help explain why some people show milder symptoms of illness while others become seriously ill,” co-author Daniela Weiskopf, of La Jolla Institute for Immunology, said in a statement.

This study builds on research, published in the journal Cell in May by the same team, that detected these SARS-CoV-2-responsive T cells in 40 to 60 percent of people who had never had COVID-19.

Lasting immunity?

The vaccines currently under development for the new coronavirus try to trigger both types of immune response.

Earlier attention, however, has largely focused on the immunity conferred by antibodies.

“But we should not think that nothing else exists,” Yonathan Freund, professor of emergency medicine at the hospital in Pitie-Salpetriere in Paris, told AFP.

Studies have shown that the level of antibodies in patients who have had COVID-19 drops rapidly, perhaps within a few weeks.

“That could mean two things: One thing that would be catastrophic is that immunity to COVID does not last,” Freund said, adding that he doubts this is the case.

The second possibility, he said, is that potential immunity exists but “cannot be detected” by the serology tests for antibodies.

This would mean that our calculations on the percentage of the population potentially immune to the coronavirus, which are based on the detection of antibodies, could be underestimated all over the world.

A recent study at Karolinska University Hospital in Sweden showed that many people with mild to asymptomatic COVID-19 showed an immune response of T cells to the virus, even when their antibody test was negative.

But Freund stressed that discussions surrounding T cells were for the most part just “hypotheses”.

And scientists would like to emphasize that thorough, large-scale research is needed before there are any implications for tackling the pandemic.

“Theories for pet (are) fine in academic debates, but dangerous when they advise for policy,” Devi Sridhar, a professor of global public health at the University of Edinburgh, said on Twitter this week.

She added that if there was clear evidence of broader public immunity or that the virus had weakened she would be “happy”.

“That’s what we all hope for. But we need to plan and prepare according to current evidence & observatory studies from around the world,” she said.

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© 2020 AFP