Can you really “chill” when the temperature drops? Science finally says yes

“I caught a cold” (this is also true). At the same time, it is cold, very cold, and like every year when the temperatures drop, everyone gets cold. From the classic cold to flu, bronchiolitis, nasopharyngitis and angina, not forgetting Covid-19, the season of respiratory infections has begun and everywhere is coughing, sniffling, blowing the nose and sneezing. Except that until now, on the words of a doctor, we caught viruses and bacteria. But “cold”, no such thing did not exist.

Except Science just reviewed its copy. According to a study published recently in Journal of Allergy and Clinical Immunology, exposure to cold will affect the antiviral immunity of the nose. How ? 20 minutes explains everything to you.

The nose, immune barrier

If the idea of ​​catching a cold was broken until now, it is because doctors and scientists explained the resurgence of respiratory infections in winter with a very specific seasonal habit. “It was generally thought that the cold and flu season occurred in the colder months because people live more indoors, where airborne viruses can spread more easily,” summarized Benjamin Bleier, co-author of the study and a surgeon at Harvard Medical School.

But whether cape, cliff, peak, peninsula or any mini, our nose protects an army of little soldiers ready to regroup into a battalion and attack any virus that would tickle our nostril. Professor Mansoor Amiji, co-author of the study and a professor at Northeastern University in Boston, discovered in previous work in 2018 that cells in the nose release extracellular vesicles (EVs), a cloud of small particles that attack the bacteria when inhaled. “The best analogy is the hornet’s nest,” says the researcher. Like hornets defending a nest when attacked, VEs fly in swarms to bond with attackers and kill them.

An immune response weakened by cold

As part of this new study, the researchers wanted to know if the nose secretes these electric cars in the presence of a virus and if their effectiveness is affected by temperature? To determine this, they used the nasal mucosa of volunteers (who were undergoing surgery to remove polyps) and a substance that mimics a viral infection. They divided the nasal mucosa into two groups, with cells grown in the laboratory at 37°C for some and at 32°C for others. Temperatures chosen from tests showing that the temperature inside the nose drops about 5°C when the outside air drops from 23°C to 4°C.

Results? Scientists have found that although the nose actually produces electric cars to fight viruses, a drop in the thermometer can affect their protective power. Under normal body temperature conditions, EVs present “decoys” to viruses to which the latter cling, instead of the cell receptors they normally target. And then the infection blocks. However, in cooler temperatures, EV production is not only less abundant, but also less effective against the viruses tested: two common rhinoviruses and a (non-Covid) coronavirus in winter. In practice, “when the thermometer drops below 5°C, the function of this immune barrier, of the antiviral response of the ENT sphere is less effective. Hence this expression of getting a cold”, suggests Dr. Benjamin Davido, specialist in infectious diseases at the Raymond-Poincaré hospital in Garches.

Future treatments and “ENT loop”

Until now, therefore, there had never been a very convincing reason to explain why there is a clear increase in viral infectivity in the colder months, emphasized Benjamin Bleier, co-author of the study and surgeon at Harvard Medical School, in a press release. “This is the first quantitatively and biologically plausible explanation.”

This work could make it possible to better understand the mechanisms of action of respiratory infections, but also to develop treatments to stimulate the natural production of EV, in order to better fight these winter viruses, Mansoor Amiji assesses: “It is an area of ​​research that interests us enormously , and we will undoubtedly continue on this path”.

Meanwhile, “while we are in the middle of meteorological winter and a triple epidemic of Covid-influenza-bronchiolitis is raging, the best thing is to wear a mask, prescribes Dr. Davido. It is not only a filter that protects against respiratory infections, that circulates actively, but it has a double protective effect: it also protects the nasal immune cells, by heating the atmosphere in the exhaled air, it is a kind of ENT scarf”.

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