Why colds and flu viruses are more common in winter

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There’s a shiver in the air, and you all know what that means — it’s time for cold and flu season, when it seems like everyone you know is suddenly sneezing, sniffling, or worse. It’s almost like those pesky cold and flu germs are whirling in with the first storm of winter weather.

Still, germs are present year round – just think back to your last summer cold. So why do people get more colds, flus and now Covid-19 when it’s cold outside?

In what researchers call a scientific breakthrough, scientists behind a new study may have found the biological reason why we get more respiratory illnesses in the winter. It turns out that the cold air itself damages the immune response in the nose.

“This is the first time we have a biological, molecular explanation for a factor of our innate immune response that appears to be limited by colder temperatures,” said rhinologist Dr. Zara Patel, a professor of ENT and head and neck surgery at Stanford. California University School of Medicine. She was not involved in the new study.

In fact, lowering the temperature in the nose by just 9 degrees Fahrenheit (5 degrees Celsius) kills nearly 50% of the billions of virus and bacteria-fighting cells in the nostrils, according to the study published Tuesday in The Journal of Allergy and Clinical Immunology .

“Cold air is associated with increased viral infection because you’ve basically lost half your immunity from that small drop in temperature,” says rhinologist Dr. Benjamin Bleier, director of otolaryngology at Massachusetts Eye and Ear and associate professor at Harvard Medical Schools. in Boston.

“It’s important to remember that these are in vitro studies, which means that while it’s using human tissue in the lab to study this immune response, it’s not a study done in someone’s nose,” Patel said in an e-mail. -mail. “Often the findings 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 the hunt for scientific detectives.

A respiratory virus or bacteria enters 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 is aware of the intruder, the team found.

At that point, cells lining the nose immediately begin making billions of simple copies of themselves, called extracellular vesicles, or EVs.

“EVs can’t divide the way cells can, but they’re like little mini versions of cells that are specially designed to kill these viruses,” Bleier said. “EVs act as decoys, so now when you breathe in a virus, the virus sticks to these decoys instead of the cells.”

Those “Mini Me’s” are then expelled by the cells into nasal mucus (yes, snot), 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 leaves your body to fight the bacteria and viruses before they actually get into your body,” Bleier said.

Once created and dispersed in nasal secretions, the billions of EVs begin to swarm the marauding germs, Bleier said.

“It’s like kicking a wasp’s nest, what happens? You might see a few hornets flying around, but if you kick them, they’ll all fly out of the nest to attack before that animal can get into the nest itself,” he said. “That’s the body’s way of clearing these inhaled viruses so they can never get into the cell in the first place.”

When the nose is attacked, extracellular vesicle production increases by 160%, the study found. There were other differences: EVs had many more receptors on their surface than native cells, boosting the virus-inhibiting power of the billions of extracellular vesicles in the nose.

“Imagine receptors as little arms sticking out and trying to grab hold of the viral particles as you breathe them in,” Bleier said. “And we found that each vesicle has up to 20 times more receptors on its surface, making them super sticky.”

Cells in the body also contain a viral killer called micro-RNA that attacks invading germs. Yet EVs in the nose contain micro-RNA sequences 13 times more than normal cells, the study found.

So the nose comes into battle armed with some extra super powers. But what happens to those benefits when it gets colder?

To find out, Bleier and his team exposed four study participants to 15 minutes of 40-degree Fahrenheit (4.4 degrees Celsius) temperatures, then measured the conditions in their nasal cavities.

“What we found is that when you are exposed to cold air, the temperature in your nose can drop by as much as 9 degrees Fahrenheit. And that’s enough to essentially knock out all three of the immune benefits that the nose has,” Bleier said.

In fact, that little bit of cold at the tip of the nose was enough to take nearly 42% of the extracellular vesicles out of the fight, Bleier said.

“Similarly, you have almost half the amount of those killer micro-RNAs in each vesicle, and you can have up to 70% fewer receptors on each vesicle, making them much less sticky,” he said.

What does that do to your ability to fight off colds, flu and Covid-19? It reduces your immune system’s ability to fight respiratory infections by half, Bleier said.

As it turns out, the pandemic has given us exactly what we need to fight cold air and keep our immunity high, Bleier said.

“Masks not only protect you from the direct inhalation of viruses, but it’s like wearing a sweater on your nose,” he said.

Patel agreed: “The warmer you can keep the intranasal environment, the better this innate defense mechanism will be able to work. Maybe another reason to wear masks!”

In the future, Bleier expects to see the development of topical nasal medications that build on this scientific revelation. These new drugs will “essentially fool the nose into thinking it just saw a virus,” he said.

“By having that exposure, all these extra hornets will be flying around in your mucous membrane to protect you,” he added.

The Valley Voice
The Valley Voicehttp://thevalleyvoice.org
Christopher Brito is a social media producer and trending writer for The Valley Voice, with a focus on sports and stories related to race and culture.

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