A person's immune system's memories of old colds caused by less harmful coronavirus relatives could be an explanation for why covid-19 affects different people so differently.
Previous studies from La Jolla Institute in the United States and a Swedish study from the Karolinska Institute released in June found that people who have not tested positive for antibodies for Covid-19 can still show what’s known as T-cell-mediated immunity to the virus.
In a study earlier this year, the researchers from the La Jolla Institute of Immunology in the United States, discovered that between 20 and 50 percent of people who have not been exposed to Covid-19 still carry T-cells that seem to recognize and act on the new coronavirus.
These are so-called memory T-cells, a different part of the specific immune system than our antibodies, which also learn to recognize certain infectious agents, in order to be able to attack them if we become infected again.
The theory is that these people had previously been infected by the ’kinder’ cousins of the covid-19 virus, the coronavirus that causes colds, and that they still have a T-cell defense against them, which also reacts to covid-19.
To be completely sure that their samples really came from people who had not been exposed to covid-19 infection, the same researchers carried out a new study, looking at samples from between 2015 and 2018, when covid-19 did not exist. In them they found T-cells that reacted both to virus sequences of the kinder cold virus and the new coronavirus (Covid-19) or sars-cov-2.
The studies suggest that parts of the population that have previously had this type of cold, carry a dormant immune system, which gives them a head start - a protection that makes them not as ill, or maybe not even get any symptoms at all. "But before we know it more studies on both humans and animals are needed," Marcus Buggert from Karolinska Institute says.
The Brussels Times