Scientists may now have an answer to one of the most crucial lingering questions about COVID-19: whether humans develop long-term immunity.
An early spate of research suggested that coronavirus antibodies – blood proteins that protect the body against subsequent infections – could disappear within months. But in their concern about the implications of these findings, many people failed to consider our multi-layered defense of our immune system against invading pathogens.
Specifically, they reduce the role of white blood cells, which have impressive memory capabilities that can help your body mount another attack against the coronavirus if it ever returns. Memory T cells are a particularly key type because they identify and destroy infected cells, and B cells inform you about how to make new virus-targeted antibodies.
A study published in the journal Cell on Friday suggests that anyone who gets COVID-19 – even people with mild or asymptomatic cases – develops T cells that can fight the coronavirus if they are later exposed again. .
“Memory T cells are likely to prove critical for long-term immune protection against COVID-19,” the study’s authors wrote, adding that they “may prevent recurrent episodes of severe COVID-19.”
This is because T cells for memory can stick to you for years, while antibody levels drop after an infection.
Even patients without antibodies have virus-specific T cells
A human T lymphocyte (also called a T cell) from a healthy donor’s immune system.
NIAID
The authors of the new study examined the blood of 206 people in Sweden who had COVID-19 with varying degrees of severity. They found that, regardless of whether a person had recovered from a mild or severe case, they still developed a robust T-cell response. Even patients with coronavirus who did not test positive for antibodies in all T cells developed memory, the results showed.
Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, called T-cell studies like this “good news.”
“There’s been a lot of hot stuff happening at the moment” in T cell research, Fauci said during a NIAID Facebook Live interview on Thursday, adding, “people who do not seem to have high titers of antibodies, but those they are infected, if infected, have good T cell responses. “
Dr. Anthony Fauci, Director of the National Institute of Allergy and Infectious Diseases.
Mandel Ngan / AFP via Getty Images
Other recent research supports the new findings.
A study published in July found that in a group of 36 recovered coronavirus patients, all produced T-memory cells that were recognized and made specifically to fight the new coronavirus. Another recent study published in the journal Nature found that among 18 German coronavirus patients, more than 80% developed virus-specific T cells.
Even people who have never been exposed to the new coronavirus can have protective T cells
Both of those earlier studies also yield a second, more surprising finding: Many people who have never received COVID-19 appear to have T-memory that can recognize the new coronavirus.
That was true for more than half of a cohort of 37 people in the July study, and at least a third of a group of 68 patients in the Nature study.
Clinicians take blood samples to look for coronavirus antibodies in a recovered COVID-19 patient.
REUTERS / Shannon Stapleton
The most likely explanation for these findings is a phenomenon called cross-reactivity: when T cells develop in response to another virus, they respond to a similar, but previously unknown, pathogen. In this case, experts think that these cross-reactive T cells are likely to come from previous exposure to other coronaviruses – the ones that normally cause colds.
Indeed, a study published earlier this month supports this hypothesis: Researchers reported that 25 people who had never had COVID-19 had T-memories that could recognize both the new coronavirus and the four types of common-cold coronaviruses alike.
“This may help explain why some people experience milder symptoms of illness while others become seriously ill,” Alessandro Sette, an associate of that research, said in a press release.
“You start with a bit of an advantage – an advance in the arms race between the virus that wants to reproduce and the immune system that wants to eliminate it,” Sette told Business Business earlier.
We still do not know exactly how long this immunity will last in the long run
Blood samples in vials will be tested for coronavirus antibodies at Keele University in the United Kingdom, 30 June 2020.
REUTERS / Carl Recine
Although this news about T cells and immunity to coronavirus is promising, scientists still do not know exactly how long people who recover from COVID-19 will be protected from future infection.
The authors of the new study said they detected T cells “months after infection, even in the absence of detective circulating antibodies.”
Another preliminary study, published Saturday, suggests that T cells not only last three months after symptoms of coronavirus begin, but in some cases increase in number during this time.
What’s more, evidence obtained from other coronaviruses, such as SARS, suggests that the lifespan of T cells can be decades long.
The July study also looked for T cells in blood samples from 23 people who survived SARS. Sure enough, those survivors still had SARS-specific memory T cells 17 years after they became ill. The same T cells could also recognize the new coronavirus.
