A newly discovered immune response inside the nose could explain why respiratory illnesses like RSV, Covid, the common cold and flu thrive in winter, according to research published Tuesday in The Journal of Allergy and Clinical Immunology, a finding that challenges the conventional wisdom that infections spread because people are stuck indoors and signposts ways to develop new treatments.
When faced with bacterial intruders, research shows that cells in the front of the nose unleash a barrage of small fluid-filled sacs as part of an immune response designed to attack and neutralize possible threats.
Based on experiments exposing nasal cell and tissue samples to three viruses that cause the common cold—two rhinoviruses and a coronavirus (not the one responsible for Covid-19)—the research showed the nose also uses the tactic to defend against viral threats.
To test whether colder conditions affect this response, the researchers used healthy volunteers to measure how much the temperature inside the nose dropped after moving from a room temperature environment and spending 15 minutes at around 40°F (4.4° C).
The researchers exposed the nasal cell samples to a similar drop in temperature—around 9°F (5° C)—to emulate the real-world drop.
The immune response was markedly reduced at this lower temperature, the researchers found, which they said gives the first biological mechanism explaining why viral illnesses are common in winter.
The findings signpost potential directions for future research testing the finding with other viruses and in humans and animals, the researchers said, as well as developing new treatments such as nasal sprays.
“We’ve uncovered a new immune mechanism in the nose that is constantly being bombarded, and have shown what compromises this protection,” said one of the study’s authors, Dr. Mansoor Amiji, a professor at Northeastern University’s School of Pharmacy. “The question now changes to, ‘How can we exploit this natural phenomenon and recreate a defensive mechanism in the nose and boost this protection, especially in colder months?’”
Though there is a clear and obvious connection linking cold weather and illnesses like the common cold, experts have been less clear as to why this connection exists. The common dictate that you can catch a cold from the cold is simplistic. One must obviously encounter the virus as well to be infected. Over the years researchers have pointed to a number of different factors to explain the phenomenon, including the colder weather bringing people into closer contact, viruses lasting longer in colder, drier conditions and drops in physical activity and sunlight during winter. The new biological explanation does not supplant any of these explanations and the seasonal patterns are very unlikely to have a single cause.
Measures put in place to guard against Covid-19 during the pandemic dampened the usual gamut of respiratory infections like RSV (respiratory syncytial virus), the common cold and flu. Many of these are now making comebacks and are expected to collide with a spike in Covid as well. Pediatric hospitals in the U.S. are already struggling with the surge in RSV, which is particularly dangerous to very young children, as well as the elderly.
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