The research focused on a sample of families, made up of adults and children, living in confined homes during the spring of 2020 in the metropolitan area of Barcelona. After analysing saliva samples from all participants, 96.3% were found to contain the soluble protein sACE2.

ACE2 is a protein found on the surface of cells in different tissues of the human body, including the lungs. When the COVID-19 virus comes in contact with people, it binds to the ACE2 protein and can enter cells, replicate and cause infection. The soluble form of this enzyme, sACE2, is released in small amounts into blood and other body fluids, such as saliva, and can circulate freely. It is believed that sACE2 may play a protective role against SARS-CoV-2 by binding to the virus and neutralizing it before it can infect cells.

“We observed that children who had not been infected with SARS-CoV-2 had a higher concentration of sACE2 in saliva samples than infected children and adults,” explained the lead authors of the study. “This could be another factor that explains why the children had milder symptoms.”

Findings from the research group, led by Samuel Bru, Pedro Brotons and Carmen Muñoz-Almagro, of the Faculty of Medicine and Health Sciences, suggest that the release of adequate concentrations of sACE2 in saliva may have a protective effect against SARS-CoV-2. Specifically, the research identified forms of the soluble protein found mainly in children’s saliva.

The study authors point out that these findings could have important implications for future research on the virus, such as helping to predict the risk of infection based on sACE2 levels or whether they can be used as biomarkers to identify people most susceptible to infection.

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