A team of specialists from the University of Massachusetts Eye and Ear Research and Northeastern University has identified the exact and previously unknown mechanism of the nasal immune response. This explains the increased likelihood of contracting SARS during the cold season. The findings of the work are published in the Journal of Allergy and Clinical.

“Cold and flu season was thought to occur during the cooler months because people linger more indoors, where viruses spread more easily through airborne droplets,” said one of the study’s authors. Now, scientists have found that the root cause of seasonal fluctuations in viral diseases of the upper respiratory tract are biological factors.

Previous work also showed that cells in the front of the nose identified bacteria and then released billions of tiny, fluid-filled particles — extracellular vesicles, or exosomes — that penetrated the mucus and attacked the pathogens.

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The new study analyzed how cells and tissue samples from the noses of surgical patients and healthy volunteers reacted to three viruses: one coronavirus and two rhinoviruses that cause colds.

They noticed that each pathogen activates the exosome response from the cells of the nose, although it uses a different signaling pathway from that which occurs to fight bacteria. In addition, it was possible to elucidate the mechanism responsible for the antiviral reaction: when they penetrated, extracellular vesicles acted as bait, transferring elements to which the virus binds instead of nasal cells.

The authors then tested how lower temperatures affect this process, given that the internal temperature of the nose is highly dependent on the temperature of the outside air. For this, healthy subjects who were at room temperature were studied. After being subjected, they were placed for 15 minutes in a space where it was 4.4 degrees Celsius. It turned out that the temperature inside the nasal cavity dropped by about five degrees Celsius. The same experiment was carried out on nasal tissue samples, which resulted in a slower immune response. The number of exosomes secreted by nasal cells decreased by almost 42 percent, and the functioning of antiviral proteins was also impaired in them.

Future studies plan to conduct similar tests with other pathogens. In the future, this will allow the development of new therapeutic agents to activate and enhance the immune response of the nose - for example, a nasal spray to increase the number of extracellular vesicles.