A recent study suggests that infection from previous ‘common cold’ coronaviruses may provide some immunity to individuals exposed to SARS-CoV-2.
The reason why some individuals experience severe symptoms from infection whilst others experience mild or no symptoms has baffled the scientific community. Research groups are currently undertaking a series of studies, including the GenOMICC COVID-19 study, to investigate this question. Undoubtedly, studying this question will take years and the answer is likely to be multi-faceted.
Researchers are already aware of several factors which influence severity, including age, ethnicity/race and health co-morbidities. However, a team of scientists from Germany have identified another potentially vital factor – previous exposure to coronaviruses.
In this study, the team investigated CD4+ T cells also known as T-helper cells. CD4+ T cells are specialised T cells that are essential in regulating the immune response. They studied these cells from the peripheral blood of 18 patients with COVID-19 and 68 SARS-CoV-2 unexposed healthy donors.
The team stimulated these CD4+ T cells using small synthetic fragments of the SARS-CoV-2 spike protein (S protein). They detected S-reactive CD4+ T cells in 83% of patients with COVID-19. The researchers expected this result as patients’ immune systems were in the process of fighting this novel virus so this would also be expected in vitro.
Surprisingly, however, the team found memory CD4+ T cells in healthy donors that recognised fragments of SARS-CoV-2. They found that 35% of healthy donors also had S-reactive CD4+ T cells.
The S-reactive CD4+ T cells found in healthy donors showed significantly stronger reactions to a different fragment of the protein than patients with COVID-19. This fragment exhibited a higher similarity to previous endemic ‘common cold’ coronaviruses. This suggests that the reactivity seen in healthy donors may originate from previous immune responses to ‘common cold’ coronaviruses.
Dr Claudia Giesecke-Thiel, one of the three lead authors on the paper, explained:
“One of the characteristics of T-helper cells is that they are not only activated by a pathogen with an ‘exact fit,’ but also by pathogens with ‘sufficient similarity’.”
The exact impact this cross-reactivity may have on SARS-CoV-2 infection is not clear. Nonetheless, these results raise questions as to whether pre-existing S-reactive CD4+ T cells may have a protective role in SARS-CoV-2 infection. If this is the case, this may contribute to our understanding of the virus’ diverse clinical manifestations.
Charité-Universitätsmedizin Berlin and the Max Planck Institute for Molecular Genetics (MPIMG) are leading a study to address these questions. They will be investigating whether this cross-reactivity has a protective effect on SARS-CoV-2 infection. The researchers will follow COVID-19 risk populations over several months to help predict the clinical course of COVID-19.