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Immune system fights COVID-19 best when it fights together, La Jolla scientists report

A cell, in greenish brown, is heavily infected with the coronavirus that causes COVID-19.
(National Institute of Allergy and Infectious Diseases)

The immune system’s best chance at fighting off the coronavirus that causes COVID-19 is to work as a single unified force, something that doesn’t happen as readily in older adults, according to a study by scientists at the La Jolla Institute for Immunology.

In the study, published Sept. 16, researchers found that people with milder cases launched a multipronged counterattack against the virus, blocking infection and clearing infected cells. But the immune systems of adults 65 and older don’t do that nearly as well as younger groups.

The finding may help explain one of the most baffling aspects of COVID-19 — why the disease puts some people on ventilators while others develop few, if any, symptoms. The authors say the lessons learned from this study could affect the kinds of immune responses researchers measure in COVID-19 vaccine trials.

“It’s a very clean, authoritative study,” said Dennis Burton, a Scripps Research Institute immunologist who was not involved in the work.

The scientists measured immune responses in blood samples from more than 50 San Diegans, including those who have recovered from COVID-19, people currently battling the disease and local residents who haven’t been exposed to the coronavirus.

From those samples, researchers looked at two key immune players: antibodies, proteins that latch onto a virus and can prevent infection; and T cells, which kill infected cells and direct the overall scale and strategy of an immune response.

COVID-19 patients with strong antibody and T cell responses tended to have milder disease. But even a T cell response alone was helpful, though antibodies on their own were not. Most vaccine research focuses on getting the body to produce antibodies, not T cells, according to Shane Crotty, the study’s senior author.

“If you have a vaccine that has a decent antibody response but maybe can’t stop everything and you still get an infection, you really want those T cells to be present to go ahead and mop it up,” Crotty said.

Burton, who is an antibody expert, said the findings agree with what scientists have long known about how the body usually responds to viral infections.

“The first time you encounter a virus, it’s the T cells that do the job,” Burton said. “The next time, and this is the principle of vaccination, you hope the antibodies are going to kick in.”

Adults 65 and older were less likely to have dual T cell and antibody responses. Part of the issue seems to be that older adults have fewer T cells that can respond to new infections — a well-established aspect of how the immune system changes with age, but a disadvantage when dealing with a new virus.

The findings, Crotty said, underscore the importance of making sure any COVID-19 vaccine sparks strong T cell responses in older adults. He said his team is eager to lend its expertise to decipher data from ongoing COVID-19 vaccine trials.

Going forward, the researchers plan to confirm their results in larger-scale studies. And they’d like to test whether the T cells most helpful in fighting off COVID-19 also recognize other coronaviruses that cause the common cold. If so, that could mean that exposure to those older cousins of this coronavirus protect against COVID-19.

“We almost talk about it every day,” Crotty said.