A team of scientists has discovered new immune responses that help explain why some individuals do not contract COVID-19. Researchers from the Wellcome Sanger Institute, University College London (UCL), Imperial College London, and the Dutch Cancer Institute studied immune responses against SARS-CoV-2 infection in 36 healthy adult volunteers who did not get COVID-19. This allowed the team to identify unique immune responses associated with resistance to viral infection and ongoing disease.
As part of the study, volunteers were administered the SARS-CoV-2 virus nasally. The scientists conducted detailed monitoring of blood and nasal lining, tracking the entire infection process along with immune cell activity before the infection itself for 16 volunteers. They then used single-cell sequencing to create a dataset comprising over 600,000 individual cells.
The team discovered responses that had "not been previously reported" among all participants related to the immediate detection of the virus. This included the activation of specialized mucosal immune cells in the blood and a decrease in inflammatory white blood cells that typically engulf and destroy pathogens. Individuals who eliminated the virus quickly did not exhibit the typical broad immune response; instead, they developed unprecedented subtle innate immune responses.
The study explained that high levels of activity of a gene called HLA-DQA2 also help individuals prevent ongoing infections. In contrast, the six individuals who experienced ongoing SARS-CoV-2 infection displayed a rapid immune response in the blood but a slower immune response in the nose, allowing the virus to spread in that area.
Dr. Marco Nicolitch, the senior author of the study, stated, "These results shed new light on the critical early events that either allow the virus to take control of the body or eliminate it quickly before symptoms appear." The findings, published in the journal Nature, provide the most comprehensive timeline to date of how the body responds to SARS-CoV-2 or any infectious disease.
