Since the first cases of coronavirus were identified in December 2019 in Wuhan, China, researchers have known that some people are more prone to catching the highly infectious virus, are more likely to experience a severe infection, and are more likely to die as a result of it, than others. For the last several months they have been attempting to understand why this is the case. According to one new study, it could have to do with the fact that some people’s immune systems have some familiarity with the pathogen — even though they have never been exposed to it.
Immune-Boosting Cells Play a Part
In the study, published in the journal Nature on Wednesday, researchers from Germany and the United Kingdom sampled 68 health adults in Germany, none of whom had ever been exposed to coronavirus. However, over a third of them — 35% — had T cells (immunity-boosting cells that help protect your body from infection) that were reactive to the virus. This would mean that their immune system could have battled a similar infection — possibly another type of coronavirus — and be able to use its memory to fight coronavirus. This is called “cross-reactivity.” They also analyzed blood samples from 18 COVID-19 patients, finding 83% had T cells reactive to the virus.
“This was exactly what we had expected. The immune system in these patients was in the process of fighting this novel virus, and therefore showed the same reaction in vitro,” explained one of the study’s three lead authors, Claudia Giesecke-Thiel, Ph.D., head of the flow cytometry facility at the Max Planck Institute for Molecular Genetics.
“The fact that not all patients with COVID-19 showed this T-helper cell response to viral fragments is probably due to the fact that T cells cannot be activated outside the human body during an acute or particularly severe phase of an illness.”
Still, You Could Get Infected
However, it still isn’t clear of the impact these cells could have on the overall outcome of a COVID-19 infection.
“Generally speaking, it is possible that cross-reactive T-helper cells have a protective effect, for instance, by helping the immune system speed up its production of antibodies against the novel virus,” explained co-lead author Leif Erik Sander, MD, of Charité’s medical department, division of infectious diseases and respiratory medicine.
“In this case, a recent bout of the common cold would probably result in less severe COVID-19 symptoms. However, it is also possible that cross-reactive immunity could lead to a misdirected immune response and potentially negative effects on the clinical course of COVID-19. We know this can occur with dengue fever, for instance.”