“You’re going to catch a cold!” » Doctors have often looked down on this popular expression. Can we really develop a respiratory or ENT disease because of the cold? No, they thought. Winter temperatures cannot be directly responsible for our colds, flu, sore throats, ear infections and other ailments, which are, as everyone knows, much more frequent in the bad season.
An American study published on December 5 proves them wrong: this popular belief was true! When our nasal mucous membranes breathe icy air, show the authors, this cold neutralizes one of our body’s first lines of defense against a viral attack. Weakened, they leave the field open to the virus, which invades our respiratory tract.
Until now, two explanations prevailed to account for the higher frequency of respiratory diseases in winter. The first is behavioral. During the cold season, we live more in a closed environment. These prolonged stays in closed places, with the promiscuity they entail, promote infections: we then breathe contaminated air. Second mechanism, the viruses responsible for respiratory diseases are more resistant to frost, hence their repeated offensives in the cold season.
“Very varied functions”
The biological mechanism discovered today does not invalidate these two explanations: it is complementary to them. You must first know that in case of microbial invasion in our nose, an unusual regiment intervenes urgently: it recruits microscopic soldiers all round.
“All human cells secrete tiny beads, hardly bigger than viruses”, explains Clotilde Théry, director of research at the National Institute of Health and Medical Research (Inserm, Curie Institute, Paris). Surrounded by a double layer of lipids, these nanoscopic balls (their diameter is between 50 and 200 billionths of a meter) can contain different molecules of interest.
Since 2012, these beads have captivated a learned assembly, the International Society of Extracellular Vesicles, whose vast knowledge is not proportional to notoriety. “I have been working on these vesicles for more than twenty years”testifies Clotilde Théry, who co-founded this “club” of some 2,000 members around the world.
“Extracellular vesicles were discovered in the mid-twentiethe century, explains Clotilde Théry. They gradually appeared heterogeneous and their functions very varied. » Some are used as bins for the cells – which thus get rid of their waste. Others act as messengers. Shuttles between cells, they transport missive molecules (proteins, RNA molecules).
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