Important differences in how the nasal cells of young and elderly people respond to the SARS-CoV-2 virus, could explain why children typically experience milder COVID-19 symptoms, finds a new study led by researchers at UCL and the Wellcome Sanger Institute.
The study, published in Nature Microbiology, focused on the early effects of SARS-CoV-2 infection on the cells first targeted by the viruses, the human nasal epithelial cells (NECs).
These cells were donated from healthy participants from Great Ormond Street Hospital (GOSH), University College London Hospital (UCLH) and the Royal Free Hospital, including children (0-11 years), adults (30 - 50 years) and, for the first time, the elderly (over 70 years).
The cells were then cultured using specialised techniques, allowing them to regrow into the different types of cells you originally find in the nose. Using single-cell RNA sequencing techniques that enable scientists to identify the unique genetic networks and functions of thousands of individual cells, the team identified 24 distinct epithelial cell types. Cultures from each age group were then either mock infected or infected with SARS-CoV-2.
The researchers found that, after three days, the NECs of children responded quickly to SARS-CoV-2 by increasing interferon (the body's first line of anti-viral defence) - restricting viral replication. However, this early anti-viral effect became less pronounced with age.
The researchers also found that NECs from elderly individuals not only produced more infectious virus particles, but also experienced increased cell shedding and damage.
The strong antiviral response in the NECs of children could explain why younger people typically experience milder symptoms. In contrast, the increased damage and higher viral replication found in NECs from elderly individuals could be linked to the greater severity of disease observed in older adults.
