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There’s a chill in the air, and you all know what that means: It’s that time of cold and flu season, when it seems like everyone you know is suddenly sneezing, sniffling, or worse. It’s almost as if those pesky cold and flu germs are swarming with the first blast of winter weather.
However, the germs are present throughout the year; just remember your last summer cold. So why do people get more colds, flu and now Covid-19 when it’s cold outside?
In what researchers are calling a scientific breakthrough, scientists behind a new study may have found the biological reason why we get more respiratory illnesses in winter. It turns out that the cold air itself damages the immune response that occurs in the nose.
“This is the first time we have a biological and molecular explanation for a factor in our innate immune response that appears to be limited by colder temperatures,” said rhinologist Dr. Zara Patel, professor of otorhinolaryngology and head and neck surgery at Stanford. University of California School of Medicine. She did not participate in the new study.
In fact, lowering the temperature inside the nose by as little as 9 degrees Fahrenheit (5 degrees Celsius) kills nearly 50 percent of the billions of cells that fight viruses and bacteria in the nostrils, according to the study published Tuesday in The Journal of Allergy. and Clinical Immunology.
“Cold air is associated with an increase in viral infection because you’ve basically lost half of your immunity with just that small drop in temperature,” said rhinologist Dr. Benjamin Bleier, director of otolaryngology at Massachusetts Eye and Ear and associate professor at Harvard Medical. Boston School.
“It’s important to remember that these are in vitro studies, meaning that even though you’re using human tissue in the lab to study this immune response, it’s not a study that’s done inside someone’s actual nose,” he said. Patel said in an email. “Often, the results of in vitro studies are confirmed in vivo, but not always.”
To understand why this happens, Bleier and his team and co-author Mansoor Amiji, who chairs the department of pharmaceutical sciences at Northeastern University in Boston, went on a scientific detective hunt.
A virus or respiratory bacteria invade the nose, the main point of entry into the body. Immediately, the front of the nose detects the germ, long before the back of the nose notices the intruder, the team discovered.
At this point, the cells lining the nose immediately start making billions of simple copies of themselves called extracellular vesicles, or EVs.
“EVs can’t divide like cells, but they’re like little versions of cells specifically designed to kill these viruses,” Bleier said. “EVs act as decoys, so now when you inhale a virus, the virus sticks to those decoys instead of sticking to cells.”
Those “Mini Me’s” are then expelled by the cells into the nasal mucus (yes, mucus), where they stop invading germs before they can reach their destination and multiply.
“This is one of, if not the only part of the immune system that your body leaves to fight bacteria and viruses before they enter your body,” Bleier said.
Once created and dispersed in nasal secretions, the billions of EVs begin swarming the marauding germs, Bleier said.
“It’s like kicking a hornet’s nest, what’s going on? You might see a few wasps flying around, but when you kick them, they all fly out of the nest to attack before the animal can get into the nest,” he said. “That’s the body’s way of clearing these inhaled viruses so they can never enter the cell in the first place.”
When under attack, the nose increases extracellular vesicle production by 160%, the study found. There were additional differences: EVs had many more receptors on their surface than the original cells, thus increasing the virus-stopping ability of the billions of extracellular vesicles in the nose.
“Think of the receptors as little arms that stick out, trying to grab the viral particles as you breathe them in,” Bleier said. “And we found that each vesicle has up to 20 times more receptors on the surface, which makes them very sticky.”
The body’s cells also contain a viral killer called micro RNA, which attacks invading germs. However, EVs in the nose contained 13 times as many microRNA sequences as normal cells, the study found.
So the nose comes into battle armed with some extra superpowers. But what happens to these advantages when the cold comes?
To find out, Bleier and his team exposed four study participants to temperatures of 40 degrees Fahrenheit (4.4 degrees Celsius) for 15 minutes and then measured conditions inside their nasal cavities.
“What we found is that when you’re exposed to cold air, the temperature of the nose can drop as low as 9 degrees Fahrenheit. And that’s enough to essentially eliminate all three immunological advantages that the nose has,” Bleier said.
In fact, that little bit of cold on the tip of the nose was enough to knock almost 42 percent of the extracellular vesicles out of the fight, Bleier said.
“Likewise, you have almost half the amount of these killer micro RNAs inside each vesicle, and you can have up to a 70% drop in the number of receptors in each vesicle, making them much less sticky “, he said.
How does this affect your ability to fight off colds, flu and Covid-19? It cuts your immune system’s ability to fight respiratory infections in half, Bleier said.
As a result, the pandemic gave us exactly what we needed to help fight the cold air and keep our immunity high, Bleier said.
“Masks not only protect you from directly inhaling viruses, but it’s like wearing a sweater over your nose,” he said.
Patel agreed: “The warmer you can keep the intranasal environment, the better this innate immune defense mechanism is able to function. Perhaps one more reason to wear masks!”
In the future, Bleier hopes to see the development of topical nasal medications that build on this scientific breakthrough. These new pharmaceuticals “will essentially trick your nose into thinking you’ve just seen a virus,” he said.
“By having that exposure, you’re going to have all these extra wasps flying around your mucosa protecting you,” he added.