Immune system's T cells play bigger role in reducing COVID-19 severity: Study

Vaccine candidates for COVID-19 should elicit a broad immune response that includes antibodies, and body's helper and killer T cells, according to a study which says weak or uncoordinated immunity may lead to a poor disease outcome.

research, published in journal Cell, confirms that a multi-layered, virus-specific immune response is important for controlling vel coronavirus during acute phase of infection and reducing COVID-19 disease severity.

"Our observations could also explain why older COVID-19 patients are much more vulnerable to disease," said study senior author Shane Crotty from La Jolla Institute for Immulogy in US.

"With increasing , reservoir of T cells that can be activated against a specific virus declines and body's immune response becomes less coordinated, which looks to be one factor making older people drastically more susceptible to severe or fatal COVID-19," Crotty said.

In research, scientists collected blood samples from 50 COVID-19 patients and analysed multiple branches of ir immune system -- vel coronavirus specific antibodies, helper and killer T cells.

"It was particularly important to us to capture whole range of disease manifestation from mild to critically ill so we could identify differentiating immulogical factors," said study co-author and infectious disease specialist Sydney Ramirez.

researchers found that all fully recovered individuals had measurable antibody, helper and killer T cell responses against vel coronavirus SARS-CoV-2.

However, y said response varied widely in acute COVID-19 patients, with some lacking neutralising antibodies, ors helper or killer T cells or any combination reof.

"When we looked at a combination of all of our data across all 111 measured parameters we found that in general, people who mounted a broader and well-coordinated adaptive response tended to do better," said Carolyn Moderbacher, ar co-author of study from La Jolla Institute for Immulogy.

"A strong SARS-CoV-2 specific T cell response, in particular, was predictive of milder disease. Individuals whose immune response was less coordinated tended to have poorer outcomes," Moderbacher said.

scientists found that effect was magnified when y broke down dataset by .

"People over of 65 were much more likely to have poor T cell responses and a poorly coordinated immune response, and thus have much more severe or fatal COVID-19," Crotty said.

scientists explained that as people , immune system's supply of deployable immature T cells dwindles, with fewer cells available to be activated to respond to a new virus.

"This could eir lead to a delayed adaptive immune response that is unable to control a virus until it is too late to limit disease severity or magnitude of response is insufficient," Moderbacher said.

scientists believe T cells, and helper T cells, in particular, are associated with better protective immune responses.

"This was perplexing to many people, but controlling a primary infection is t same as vaccine-induced immunity, where adaptive immune system is ready to pounce at time zero," Crotty said.

"Thus, se findings indicate it is plausible T cells are more important in natural SARS-CoV-2 infection, and antibodies more important in a COVID-19 vaccine," he said.