Bacteria-fighting cells in the airways boost infection risk from viruses

Oct. 12, 2020

In a study, led by a team from Imperial College London and published in Science, researchers found that volunteers who succumbed to infection from respiratory syncytial virus (RSV) had more specialized white blood cells called neutrophils in their airways before exposure to the virus, compared to those who staved off infection, according to study results. According to the researchers, this type of neutrophil-driven inflammation in the nose and throat – typically associated with fighting off bacterial infections – may compromise our ability to fight off invading viruses and make us more susceptible to viral infections.

The findings could help researchers to understand why people respond differently to the same viral threat, predict who is more at risk of infection, and even lead to preventative treatments to protect against RSV and potentially other respiratory viruses, including influenza and coronaviruses.

Unlike other respiratory viruses, such as influenza or rhinovirus, people can be infected by the same strain of RSV more than once. People can also react differently when exposed to the virus under the same conditions – some may get a mild infection while others get full-blown symptoms, and some may avoid infection altogether. In the latest study, the team aimed to investigate the underlying mechanisms of why people succumb to RSV infection and the factors for the varied immune responses.

Healthy adults were enrolled to the study and exposed to RSV in a safe, controlled clinical setting where they were closely monitored. After receiving nasal drops containing the virus, 57 percent of volunteers became infected. Analysis of blood samples showed that the presence of protective antibodies and B and T cells could only partially explain who became infected. However, when they analyzed samples from participants’ airways taken before they were exposed to the virus, the team found evidence of neutrophil activation in the nasal mucosa – the cells lining the inside of the nose – in those who became infected with the virus.

These immune cells are known to release proteins which help create an antibacterial environment in response to a threat. But the researchers believe this antibacterial immune response may come at a cost, making a host more susceptible to viruses by effectively switching off the early warning system, letting them slip through the net to cause infection. The researchers say that if they can demonstrate the same mechanism is occurring in patient groups who are most at risk from RSV (babies under 12 months of age and adults over 65 with chronic conditions, such as COPD or asthma) it could help to identify subsets of patients most at risk. The team is set to explore the mechanism in larger patient groups as well as investigating whether the same immune mechanisms influence other viral respiratory infections, from influenza and coronaviruses.

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