Colds are back with the arrival of winter.
Among the factors favoring these common respiratory infections: more frequent gatherings indoors and viruses surviving better in the drier air between four walls.
But as to whether low temperatures actually weaken our immune system (and if so how), there is less certainty.
A study published this Tuesday in the
Journal of Allergy and Clinical Immunology
details a new way our bodies attack intruders.
And this method works best in warm weather.
These discoveries could thus make it possible to develop new treatments against the common cold and other viruses, according to Mansoor Amiji, professor at Northeastern University and co-author of this work.
A cloud of particles that attack bacteria
The starting point is a previous study he conducted in 2018. He found that cells in the nose release extracellular vesicles (EVs), a cloud of tiny particles that attack bacteria upon inhalation.
"The best analogy is that of the hornet's nest", explains Mansoor Amiji.
Like hornets defending a nest when attacked, VEs fly in swarms to attach to invaders and kill them.
The researchers then asked themselves two questions: are EVs also secreted in the presence of a virus?
And if so, is their response affected by temperature?
For their tests, the scientists used the nasal mucosa of volunteers (who were undergoing an operation to remove polyps), and a substance reproducing a viral infection.
Result: EVs are well produced against viruses.
A way to better fight colds?
To answer the second question, the nasal mucosa were divided into two groups, the cells being cultured in the laboratory either at 37°C or at 32°C.
These temperatures were chosen based on tests showing that the temperature inside the nose drops about 5°C when the outside air drops from 23°C to 4°C.
Under normal body temperature conditions, the EVs managed to fight the viruses well, by presenting them with "decoys" to which they clung, instead of the receptors of the cells that they would normally have targeted.
But with a reduced temperature, the production of EV was less abundant, and they proved to be less effective against the viruses tested.
"There has never been a very compelling reason why there is a clear increase in viral infectivity during the colder months," Benjamin Bleier, co-author of the study and surgeon at Harvard Medical School.
“This is the first quantitatively and biologically plausible explanation that has been developed.
This work could thus make it possible to develop treatments to stimulate the natural production of EV, in order to be able to better fight colds, or even the flu and Covid-19.
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