How cold weather can help you catch a cold
PPeople have long associated the cold with getting sick. With the advent of germ theory, doctors and scientists began to suspect that it wasn’t the temperature itself that made people sick, but rather that something in harsher conditions was weakening the immune system. , allowing viruses that people are exposed to — like those behind the common cold, flu, or COVID-19 — to pick up on them more easily. However, the precise reasons why cold temperatures increase susceptibility to infection have remained elusive, so seasonality is generally explained by changing human behaviors, in particular a tendency to congregate indoors to escape the colder weather.
Now the research published today (6 December) in The Journal of Allergy and Clinical Immunology proposes a mechanism that could explain how cold influences catching a cold: the defenses of nasal cells are weaker when the cells are cold. “Conventionally, cold and flu season was thought to occur in the colder months because people are more stuck indoors where airborne viruses could spread more easily,” said said study co-author Benjamin Bleier, director of translational research in otolaryngology at Mass Eye and Ear. Press release. “Our study, however, points to a biological root cause for the seasonal variation in viral upper respiratory tract infections we see each year, most recently demonstrated throughout the COVID-19 pandemic.”
See “Viruses prefer the cold”
The researchers conducted in vitro experiments on nasal cells taken from healthy human volunteers, measuring their response to three common cold-causing viruses (one coronavirus and two rhinoviruses). Under normal temperature conditions, these cells – which occur in vivo near the front of the nose and are therefore among the first encountered by an invading virus – respond to viruses by triggering the release of a “swarm” of extracellular vesicles (EV), as the study says. This is triggered by a signaling pathway slightly different from those released in response to bacteria: the Toll-like receptor 3 (TLR3) protein detects the presence of virus, and in response, initiates the immune response which ends with the release of the EV swarm.
Further analysis revealed that at typical nasal temperatures, the surfaces of EVs released in this manner were coated with receptors that the viruses tested normally use to bind to and invade nasal cells. Indeed, EV surfaces had 20 times more of these viral receptors than cell membranes, making EVs effective decoys, Bleier explains at CNN. The study also revealed that EVs were loaded with the microRNA miR-17, which neutralized the three viruses by blocking their replication.
However, when the temperature of the cells was reduced by 5°C – mirroring the temperature drop that occurred in the noses of human participants subjected to near-freezing cold – the number of EVs released by the samples of fabrics fell by 42%. These EVs also had fewer surface receptors, meaning viruses were less likely to bind to them on nasal cells, and contained less miR-17, indicating that being outside in the cold suppresses the immune system. nasal in three ways at once. However, Zara Patel, a rhinologist from Stanford University School of Medicine, who did not work on the study, cautions CNN that there is no guarantee that in vitro experiments would be replicated in vivo.
Study co-author Mansoor Amija, a pharmaceutical scientist and chemical engineer at Northeastern University, suggests in the Press release that his team’s discovery of this antiviral defense mechanism could lead to new interventions, “exploiting a natural phenomenon in the nose to inhibit viral transmission”. For example, he suggests the findings could help scientists build artificial versions of EVs that act like “viral sponges,” and he refers to the discovered miRNA as “an antiviral compound that destroys [the virus] before it infects the actual cell,” which could be further explored therapeutically.
In the meantime, the study offers further incentive to wear a mask this winter as cases of COVID-19 peak againsays Bleier CNN, saying a mask can work “like wearing a sweater over your nose.” Patel agrees: “The warmer you can keep the intranasal environment, the better this innate immune defense mechanism will be able to work,” she told the outlet.