LOS ANGELES (Dispatches) -- In a study by Stanford University School of Medicine, COVID-19 patients whose symptoms were mild, researchers found that they were more likely than sicker patients to have signs of prior infection by similar, less virulent coronaviruses.
The researchers analyzed blood samples taken from healthy donors before the COVID-19 pandemic began, meaning they’d never encountered SARS-CoV-2 -- although many presumably had been exposed to common-cold-causing coronavirus strains. The scientists determined the numbers of T cells targeting each peptide represented in the panel.
The immune cells in question, called killer T cells, roam through the blood and lymph, park in tissues and carry out stop-and-frisk operations on resident cells. The study showed that killer T cells taken from the sickest COVID-19 patients exhibit fewer signs of having had previous run-ins with common-cold-causing coronaviruses.
They found that, sure enough, COVID-19 patients with milder symptoms tended to have lots of killer-T memory cells directed at peptides SARS-CoV-2 shared with other coronavirus strains. Sicker patients’ expanded killer T-cell counts were mainly among those T cells typically targeting peptides unique to SARS-CoV-2 and, thus, probably had started from scratch in their response to the virus.
“It may be that patients with severe COVID-19 hadn’t been infected, at least not recently, by gentler coronavirus strains, so they didn’t retain effective memory killer T cells,” Mark Davis, PhD, a professor of microbiology and immunology said.