A recent study published in the journal Nature by scientists from Charité and the Max Planck Institute for Molecular Genetics (MPIMG) has found that healthy individuals possess immune cells that can recognize SARS-CoV-2, the virus responsible for COVID-19. The researchers attribute this to previous exposure to common colds caused by local coronaviruses, which may trigger cross-reactivity. The study was based on blood samples from 18 COVID-19 patients treated at a Berlin hospital and 68 individuals who had no contact with SARS-CoV-2. The researchers isolated immune cells from these samples and stimulated them with fragments of the SARS-CoV-2 spike protein. While 15 of the 18 immune cells from previously infected patients showed a strong reaction, 35% of the healthy individuals also showed a response, indicating that their immune system possesses memory cells that can recognize SARS-CoV-2.
However, there were significant differences in the immune response between the two groups. While the immune cells of previously infected patients recognized the entire length of the spike protein, the immune cells of healthy individuals could only recognize fragments that have a strong structural similarity to relatively harmless coronaviruses that have long been circulating in Europe. The researchers suggest that this indicates that the T-helper cells of healthy individuals react to SARS-CoV-2 because they have had to deal with local cold coronaviruses in the past. To investigate whether local coronaviruses actually lead to cross-reactivity with SARS-CoV-2, the researchers conducted another experiment in which the immune cells of healthy individuals were exposed to local coronaviruses. This also resulted in reactions, confirming cross-reactivity.
The researchers note that cross-reactive immunity could potentially provide better protection for the immune system by accelerating the production of antibodies against SARS-CoV-2. However, it is also possible that cross-reactive immunity could trigger a false immune response. The Charité Corona Cross Study, conducted by the Technical University of Berlin, Charité, and MPIMG, is now investigating which of these possibilities is more likely.
