Cold noses more vulnerable to catching colds

IT SEEMS there may be some truth in the
old saying that, in winter, you should cover
up your nose and keep it warm to avoid catching a cold. A new study finds one reason we catch more colds in the winter is because the immune system is less effective at lower temperatures, allowing the common cold virus in the nose – where it is cooler than in the lungs – to replicate more easily.
The most frequent cause of the common cold is a virus known as the rhinovirus. Scientists have observed that, in our airways, strains of rhinovirus replicate more readily at the cooler temperatures found in the nose, compared with that of the lungs. However, the underlying mechanism has not been clear. Now, writing in the Proceedings of the National Academy of Sciences, a team of researchers at Yale University in New Haven, CT, shows that the cells lining our airways produce a more robust antiviral response to the common cold at lung temperature than in the cooler environs of the nasal cavity.
Akiko Iwasaki, senior author and professor of immunobiology at Yale, says previous studies have tended to focus on how body temperature influences the virus. But she and her colleagues decided to investigate how it affects the immune system. For their study, using cells sampled from the airways of mice, they compared immune response to the rhinovirus at core body or lung temperature (37 °C) and at a cooler temperature (33 °C). “We found that the innate immune response to the rhinovirus is impaired at the lower body temperature compared to the core body temperature.”
Specifically, the authors note two features of the innate immune response that were more robust at the higher temperature: “RIG-I- like receptor (RLR)-dependent interferon secretion and enhanced interferon responsiveness.” They tested their finding on airway cells genetically engineered to lack this part of the immune response and found they supported higher levels of viral replication at the higher temperature.
The finding shows that varying temperature influences host immune response, rather than the virus, leading the authors to conclude “cooler temperatures can enable replication of the common cold virus, at least in part, by diminishing antiviral immune responses.” Although the study used mouse cells, the team suggests it offers clues about humans too. At any one time, around 20% of us carry the rhinovirus in our noses.
Prof. Iwasaki says “in general, the lower the temperature, it seems the lower the innate immune response to viruses,” suggesting there is some truth behind the old wives’ tale that people should keep warm, and even cover their noses, to avoid catching colds. Beyond these findings, the team hopes the study offers insights into how temperature affects immune response in other rhinovirus-induced breathing conditions, such as childhood asthma.

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