- The nose has a special immune response against viruses, but the cold seems to inhibit it.
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| A woman with a cold, in a file image. / Pixabay |
They find the explanation for why upper respiratory infections are more common in cold seasons
Researchers at Mass Eye and Ear and Northeastern University in the United States have discovered a previously unidentified immune response inside the nose that fights viruses responsible for upper respiratory infections. Further tests revealed that this protective response is inhibited by cooler temperatures, according to the authors.
The new study, published in The Journal of Allergy and Clinical Immunology, offers the first biological mechanism to explain why viruses like the common cold, flu, and COVID-19 are more likely to increase in colder seasons, according to researchers authors.
The nose is a route of entry into the body for viruses
"Conventionally, cold and flu season was thought to occur in the colder months because people spend more time indoors, where airborne viruses could spread more easily," recalls Benjamin S. Bleier, director of Otolaryngology Translational Research in Mass Eye and Ear and lead author of the study. "But our study points to a fundamental biological cause for the seasonal variation in viral upper respiratory infections that we see each year, most recently demonstrated throughout the COVID-19 pandemic."
The nose is one of the first points of contact between the external environment and the interior of the body and, as such, a likely entry point for disease-causing pathogens.
Pathogens are either inhaled or deposited directly (for example, by hand) in the front of the nose, where they work their way back through the airways and into the body infecting cells, which can lead to lead to an upper respiratory tract infection. How the airways protect themselves against these pathogens has not been well understood for a long time.
The immune response of the nose
That is until a 2018 study led by Dr. Bleier and Mansoor Amiji, Distinguished Professor of Pharmaceutical Sciences at Northeastern University, discovered an innate immune response triggered when bacteria are inhaled through the nose: Cells on the upper part of The front of the nose detect bacteria and release billions of tiny fluid-filled sacs called extracellular vesicles (or EVs, formerly known as exosomes) into the mucus to surround and attack the bacteria.
The 2018 study also showed that EVs carry protective antibacterial proteins through the mucus from the front of the nose to the back along the airways, which then protects other cells against bacteria before they reach it. too far into the body.
For the new study, the researchers sought to determine whether this immune response was also triggered by viruses inhaled through the nose, which are the source of some of the most common upper respiratory infections.
Led by the study's first author, Dr. Di Huang, a Mass Eye, and Ear and Northeastern investigator, the team analyzed how cells and nasal tissue samples collected from the noses of surgical patients and healthy volunteers responded to three viruses: a single coronavirus and two rhinoviruses that cause the common cold.
Cold inhibits response
They found that each of the viruses triggered a VE swarm response from the nasal cells, albeit using a different signaling pathway from that used to combat bacteria. The researchers also discovered a mechanism at play in the response against the viruses: Upon release, the EVs acted as decoys, carrying receptors that the virus would bind to instead of the nasal cells.
"The more decoys, the more the EVs can absorb the viruses in the mucus before the viruses have a chance to attach to the nasal cells, thus suppressing the infection," Huang adds.
The researchers next tested how colder temperatures affected this response, which is especially relevant in nasal immunity since the internal temperature of the nose is highly dependent on the temperature of the outside air that is inhaled.
They took healthy volunteers from a room temperature environment and exposed them to temperatures of 4.4°C for 15 minutes and found that the temperature inside the nose dropped by about 5°C. They then applied this temperature reduction to nasal tissue samples and observed an attenuated immune response. The amount of EVs secreted by the nasal cells decreased by almost 42%, and the antiviral proteins of EVs were also affected.
"Combined, these findings provide a mechanistic explanation for the seasonal variation in upper respiratory tract infections," concludes Huang.
References
Di Huang, Maie S. Taha, Angela L. Nocera, Alan D. Workman, Mansoor M. Amiji, Benjamin S Bleier. Cold exposure impairs extracellular vesicle swarm-mediated nasal antiviral immunity. The Journal of Allergy and Clinical Immunology (2022). DOI: https://doi.org/10.1016/j.jaci.2022.09.037
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