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People who've recovered from severe COVID-19 may have stronger long-term immune protection from reinfection than those with milder illness, researchers report.
They examined blood samples from 39 COVID-19 patients and 10 people who hadn't been exposed to the virus (their blood samples were given pre-pandemic). In all, they analyzed the expression of individual genes of more than 80,000 CD8+ T-cells.
CD8+ T-cells are immune cells that destroy virus-infected host cells, and "memory" CD8+ T-cells protect the body from reinfection by many types of viruses.
Of the COVID-19 patients, 17 had milder illness and weren't hospitalized, 13 had been hospitalized, and nine ended up in intensive care. The researchers were surprised to find that patients with milder COVID-19 had weaker CD8+ T-cell responses.
The strongest CD8+ T-cell responses were in severely ill patients who required hospitalization or intensive care.
"There is an inverse link between how poorly T-cells work and how bad the infection is," study co-author Dr. Christian Ottensmeier said in a news release from the La Jolla Institute for Immunology in California. He's a professor at the University of Liverpool in the U.K. and an adjunct professor at the La Jolla institute.
The researchers found that CD8+ T-cells in people with mild COVID-19 had signs of T-cell "exhaustion," in which cells receive so much immune system stimulation to combat viruses that they become less effective.
T-cell exhaustion in people with mild COVID-19 may reduce their chances of long-term immunity, according to the authors.
"People who have severe disease are likely to end up with a good number of memory cells," explained study co-author Pandurangan Vijayanand, a professor at La Jolla Institute. "People with milder disease have memory cells, but they seem exhausted and dysfunctional -- so they might not be effective for long enough."
The findings "suggest that suggest people with severe COVID-19 cases may have stronger long-term immunity," Vijayanand said.
This study highlights the enormous variability in how human beings react to a viral challenge, Ottensmeier said.
While the study offers important new insight into COVID-19 patients' immune response, it's limited due to its reliance on CD8+ T-cells found in blood samples, the researchers explained.
To learn more, they plan to assess T-cells in tissues hit hardest by the new coronavirus, such as the lungs, to see how they react to the virus. That's crucial because the memory T-cells that provide long-term immunity need to live in the tissues.
The study was published Jan. 21 in the journal Science Immunology.
SOURCE: La Jolla Institute for Immunology, news release, Jan. 21,2021
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