Scientists finally know why people catch more colds and flus in winter |  CNN

Scientists finally know why people catch more colds and flus in winter | CNN

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A chill is 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 sneezing, sniffling, or worse. It’s almost as if those pesky cold and flu germs arrive with the first breath of winter.

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

In what the researchers call a scientific breakthrough, the scientists behind a new study may have found the biological reason why we have more respiratory illnesses in winter. It turns out that cold air itself damages the immune response occurring 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 Dr. Zara Patel, rhinologist and professor of ear, nose and throat. laryngology and head and neck surgery at Stanford. University of California School of Medicine. She did not participate in the new study.

In fact, reducing the temperature inside the nose by as little as 9 degrees Fahrenheit (5 degrees Celsius) kills nearly 50% of the billions of cells that fight viruses and bacteria in the nostrils, according to the published study. 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 just from that little drop in temperature,” said rhinologist Dr Benjamin Bleier, director of oto- rhino-laryngology at Massachusetts Eye and Ear and associate professor at Harvard Medical. Boston School.

“It is important to remember that these are in vitro studies, which means that although he is using human tissue in the laboratory to study this immune response, it is not a study conducted. inside someone’s actual nose,” 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, has embarked on a hunt for scientific sleuths.

A respiratory virus or bacteria invades 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 found.

At this point, the cells lining the nose immediately begin to make billions of single copies of themselves called extracellular vesicles, or EVs.

“EVs can’t divide like cells, but they’re like little mini-versions of cells that are specially designed to go out and kill these viruses,” Bleier said. “EVs act like decoys, so now when you inhale a virus, the virus sticks to those decoys instead of sticking to the cells.”

These “Mini Me’s” are then expelled by the cells into the nasal mucus (yes, snot), where they stop invade germs before they reach their destination and multiply.

“It’s one of, if not the only part of the immune system that leaves your body to go fight bacteria and viruses before they actually enter your body,” Bleier said.

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

“It’s like hitting a wasp’s nest, what’s going on?” You might see a few hornets flying around, but when you hit it, they all fly out of the nest to attack before that animal can enter the nest itself,” he said. “That’s how the body sponges up these inhaled viruses so they can never enter the cell in the first place.”

When attacked, the nose increases the production of extracellular vesicles by 160%, according to the study. There were additional differences: the EVs had many more receptors on their surface than the original cells, enhancing the virus-stopping ability of the billions of extracellular vesicles in the nose.

“Just imagine the receptors as little arms sticking out, trying to grab the virus 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 super sticky.”

Body cells also contain a viral killer called microRNA, which attacks invading germs. Yet the EVs in the nose contained 13 times more microRNA sequences than normal cells, the study found.

So, the nose comes into battle armed with a few extra superpowers. But what happens to those benefits when cold weather hits?

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

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

In fact, that little bit of cold in the tip of the nose was enough to kill nearly 42% of the fight’s extracellular vesicles, Bleier said.

“Similarly, you have almost half the amount of these killer microRNAs inside each vesicle, and you can have up to a 70% drop in the number of receptors on each vesicle, making them much less sticky,” he said.

What does it do to your ability to fight off colds, flu and Covid-19? This cuts your immune system’s ability to fight respiratory infections in half, Bleier said.

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

Wearing a mask can protect you from cold air which can reduce your immunity, an expert has found.

“Not only do masks protect you from directly inhaling viruses, but it’s also 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 will be able to work. Perhaps one more 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 pharmaceuticals will “essentially trick the nose into thinking it just saw a virus,” he said.

“Having that exposure, you’ll have all those extra hornets flying into your mucous membranes to protect you,” he added.

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