Why do you get sick in winter? New science shows you the nose

New research appears to provide a clearer picture of why colds and flu are more common during the winter. The study found evidence that our nose’s innate immune response weakens in colder temperatures, giving some germs a better chance to infect the rest of the body. The discoveries, say the authors, could provide a biological explanation for the seasonal nature of many respiratory diseases.

The study comes from scientists at Northeastern University as well as Mass Eye and Ear, a teaching hospital affiliated with Harvard Medical School. In 2018, several authors Published work that suggests the body possesses a unique first line of defense against potentially dangerous bacteria inhaled through the nose. Cells near the front of the nose, they found, can release fluid-filled sacs called extracellular vesicles into our mucus, where bacteria then swarm. These sacs also appear to carry antimicrobial proteins throughout the rest of the nose, helping to protect other cells from damage as they come into contact with bacteria.

In this new research, Published tuesdaypublished in the Journal of Allergy and Clinical Immunology, scientists wanted to see if the nose has a similar defense mechanism against viruses.

They studied samples in the laboratory that were taken from healthy people and patients undergoing surgery. They found that nasal cells develop extracellular vesicles in response to mock viral infection. And when they exposed the cells to three viruses that usually cause the common cold (two rhinoviruses and a non-Covid coronavirus), the vesicles then overwhelmed them. They also found that this defense is triggered by a different pathway than how extracellular vesicles are deployed against bacteria. And the extracellular vesicles additionally acted as decoys, because they carried receptors that the viruses would latch on to instead of going after the cells.

Many respiratory infections become more common during the colder parts of the year. There are thought to be several reasons for this seasonal trend, including people crowding indoors to stay warm. But the team wanted to test whether the cold could directly affect this defense mechanism as well.

They asked healthy volunteers to endure relatively cold weather (39.9 degrees Fahrenheit) for 15 minutes and measured the change in temperature in the nose, finding that it dropped by about 10 degrees Fahrenheit. They then exposed the cells to that temperature. Compared with the normal condition, the nose’s innate immune response against the virus was not as strong in this new temperature setting, the authors found, with cells producing fewer extracellular vesicles on average.

The findings need to be replicated in other studies before they are widely accepted, and there are likely multiple factors behind the seasonal occurrence of respiratory viruses. Flu studies are, for example found that moisture plays a major role in its transmission, with warm and humid or cold and dry conditions being optimal for the spread of the virus. And some cold viruses actually are most often during the summer. But the results here suggest that biology plays a leading role in determining the timing of our vulnerability to these germs, the authors say.

“Cold and flu season has conventionally been thought to occur in the colder months because people are more indoors where airborne viruses can spread more easily,” said senior study author Benjamin Bleier, director of Otolaryngology Translational Research at Mass Eye and Ear. and senior author of the study, ua statement from the Mass. Eye and Ear. “However, our study points to a biological underlying cause for the seasonal variation in viral upper respiratory tract infections that we see each year, which was recently demonstrated during the COVID-19 pandemic.”

If these findings are supported, they could also lead to improvements in how we defend ourselves against these infections. It’s possible that we could one day create nasal sprays that can stimulate or strengthen the nasal supply of extracellular vesicles during the winter, according to the team. In the meantime, they plan to test whether this defense mechanism is triggered against other pathogens.