The immune systems of some people who have not been exposed to the novel coronavirus could have some familiarity with the pathogen — possibly helping to reduce the severity of illness if that person does get Covid-19, a new study suggests.
The study, published in the journal Nature on Wednesday, found that among a sample of 68 healthy adults in Germany who had not been exposed to coronavirus, 35% had T cells in their blood that were reactive to the virus. T cells are part of the immune system and help protect the body from infection. T cell reactivity suggests that the immune system might have had some previous experience fighting a similar infection and may use that memory to help fight a new infection.
The new study involved analyzing blood samples from 18 Covid-19 patients, ages 21 to 81, and healthy donors, ages 20 to 64, based in Germany. The study found that T cells reactive to the coronavirus were detected in 83% of the Covid-19 patients.
While the researchers also found pre-existing cross-reactive T cells in the healthy donors, they wrote in the study that the impact those cells might have on the outcome of a Covid-19 illness still remains unknown.
So how could their immune system have reactive T cells if they never had Covid-19? They were "probably acquired in previous infections with endemic" coronaviruses, the researchers — from various institutions in Germany and the United Kingdom — wrote in the new study. Using this T cell memory from another-yet-similar infection to respond to a new infection is called "cross-reactivity."
"It does appear in this study that there is a significant proportion of individuals that have this cross-reactive T cell immunity from other coronavirus infections that may have some impact on how they fare with the novel coronavirus. I think the big question is trying to jump from the fact that they have these T cells to understanding what the role of those T cells might be," said Dr. Amesh Adalja, senior scholar at the Johns Hopkins University Center for Health Security, who was not involved in the new study.
"We know, for example, children and younger adults are relatively spared from the severe consequences of this disease, and I think that one hypothesis might be that the pre-existing T cells that exist may be much more numerous or more active in younger age cohorts than in older age cohorts.”