Harvard University researchers have discovered hitherto unknown aspects of the immune response within the nose, which keeps the viruses responsible for upper respiratory tract infections at bay. In a second phase of their study, they saw that this response that protects us is inhibited when we are exposed to low temperatures, which is why we are more likely to suffer infections of this type.
The work was published in the Journal of Allergy and Clinical Immunology, and is the first explanation of the biomolecular mechanisms that make the common cold, flu and covid more frequent in autumn and winter.
“Traditionally, cold and flu season was thought to occur in the colder months because people stay home more and these viruses spread more easily at home, but our work shows there is a biological rationale for the variations. that we see every year, and that we have more recently confirmed with covid cases,” explained Benjamin Bleier, professor of otolaryngology and lead author of the study.
First line of defense… the nose
The nose is one of the first points of contact between the environment and the interior of our body and, as such, one of the entry doors for pathogens (pathogens).
Pathogens are either inhaled or deposited directly (on the hands, very typical) in the front of the nose, from where they travel to the airways, infecting cells, which leads to infection. Until now, little was known about how the body protects itself from these infections. In 2018, a study by Bleier and another expert explained how the immune response is triggered when certain bacteria are inhaled through the nose.
The cells inside detected the pathogens and released millions of tiny fluid-filled sacs (vesicles) into the mucosa to attack the bacteria in question. Bleier compared it to “hitting a hornet’s nest”.
In the study that has now come out, it can be seen that the response is the same to inhaled viruses, which are the ones that usually cause upper respiratory tract infections.
The researchers analyzed cell samples from the noses of surgery patients and healthy people for the immune response to various viruses. Each triggered a response in the defensive cells and how they released the vesicles.
When they repeated the process at low temperatures, they found that the response, which is especially prominent in the nose, was blunted and less effective. The number of vesicles released was almost 42% lower, and the proteins that fight the virus also dropped significantly.
‘Combined, these two results provide an explanation of the mechanism of seasonal variations in the number of cases of respiratory infections,’ say the scientists.
