The finding comes from a study funded by UK Research and Innovation, the National Institute for Health and Care Research, Great Ormond Street Hospital Biomedical Research Centre, Wellcome and the Chan Zuckerberg Foundation.
The study focused on the early effects of SARS-CoV-2 infection on the cells first targeted by the viruses, called human nasal epithelial cells (NECs).
The cells were donated by healthy participants from Great Ormond Street Hospital, University College London Hospital and the Royal Free Hospital.
The participants included children under the age of 11, adults aged 30 to 50 and, for the first time, adults over the age of 70.
Specialised techniques
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.
Anti-viral effect
The research, published in ‘Nature Microbiology’, 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 the disease observed in older adults.
More detailed understanding
Project lead, Dr Claire Smith, from the UCL Great Ormond Street Institute of Child Health, said:
Our research reveals how the type of cells we have in our nose changes with age, and how this affects our ability to combat SARS-CoV-2 infection.
This could be crucial in developing effective anti-viral treatments tailored to different age groups, especially for the elderly who are at higher risk of severe COVID-19.
Co-Senior author, Dr Kerstin Meyer, from the Wellcome Sanger Institute, said:
By carrying out SARS-CoV-2 infections of epithelial cells in vitro and studying the responses with single cell sequencing, we get a much more detailed understanding of the viral infection kinetics and see big differences in the innate immune response between cell types.
The importance of considering age as a critical factor
Children infected with SARS-CoV-2 rarely progress to respiratory failure, but the risk of mortality in infected people over the age of 85 remains high, despite vaccination and improving treatment options.
The research underscores the importance of considering age as a critical factor in both research and treatment of infectious diseases.
Co-senior author, Dr Marko Nikolic, from the UCL Division of Medicine, said:
It is fascinating that when we take away immune cells from nasal samples and are only left with nasal epithelial cells grown in a dish, we are still able to identify age-specific differences in our body’s response to the SARS-CoV-2 between the young and elderly to explain why children are generally protected from severe COVID-19.
Long-term implications
Dr Smith added:
Understanding the cellular differences at the initiation of infection is just the beginning.
We now hope to investigate the long-term implications of these cellular changes and test therapeutic interventions using our unique cell culture model.
This ‘gold-standard’ system is only possible with the support of our funders and the willingness of participants to provide their samples.
The team suggests that future research should consider how ageing impacts the body’s response to other viral infections.
Further information
‘Age-specific nasal epithelial responses to SARS-CoV-2 infection’ is published in ‘Nature Microbiology‘.
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