Immune System Responds Strongly in Asymptomatic COVID-19

(Reuters) -
Scanning electron micrograph of a human T lymphocyte (also called a T cell) from the immune system of a healthy donor. (NIAID/NIH)

Asymptomatic people infected with COVID-19 are mounting robust immune responses that differ from responses in those who become ill, according to a study that appears to contradict previous thinking by health experts.

Researchers studied immune system T cells in 76 symptomatic COVID-19 patients and 85 infected individuals without symptoms and reported their findings on Friday on bioRxiv ahead of peer review.

Some of these cells – CD8+ T cells – can recognize virus-infected cells and destroy them. They also produce inflammatory proteins, or cytokines, that help to prevent the virus from making copies of itself. Others known as CD4 helper T cells help the body produce B cells, which make antibodies. Everyone in the study had similar frequencies of T cells that could recognize the virus and destroy infected cells, regardless of whether they had symptoms. But the T cells of asymptomatic individuals produced higher levels of cytokines important for fighting the virus, including interferon-gamma and interleukin-2.

“What we still need to understand is whether those T cells can persist over time and offer long-term immunity,” said coauthor Antonio Bertoletti of Duke-NUS Medical School, Singapore.