Catching a cold when it’s chilly out has been dismissed by many as an unsubstantiated myth, though most of us might still remember our parents telling us to put on another jacket before heading out. Turns out, they were right! The rhinovirus, better known as the common cold virus, multiplies more efficiently in the cold. The lower the temperature, the lower the immune response, according to a new study published in published in Proceedings of the National Academy of Sciences this week.
The temperature in our lungs stays around 37 degrees Celsius, whereas the nasal cavity ranges between 33 and 35 degrees Celsius due to the ambient air we inhale. Previous work have found that rhinoviruses replicate more efficiently in the cooler nasal cavity than in the warmer lungs. However, these studies focused on how body temperature influenced the virus -- and not the relationship between temperature and immune response.
Yale’s Akiko Iwasaki and colleagues wanted to see if the temperature-dependent differences in the responses of the immune system could help rhinoviruses establish infections more easily in the nasal cavity than in the lungs. They exposed the cells that line the airways of mice to a rodent version of the rhinovirus strain at either 33 degrees or 37 degrees Celsius. Then they examined the viral replication and antiviral responses that were mounted by the immune system in the cells targeted by the virus.
The virus, they found, replicated less efficiently and produced lower levels of infectious viruses at the higher temperature. And during replication, the virus prompted more robust immune responses at the warmer temp. “The innate immune response to the rhinovirus is impaired at the lower body temperature compared to the core body temperature,” Iwasaki says in a news release.
In mice with immune deficiencies, however, the virus replicated at the higher temperature, indicating how “it’s not just virus intrinsic, but it’s the host’s response, that’s the major contributor,” Iwasaki adds. The team also discovered that two related immune system mechanisms were more active at 37 degrees than at 33 degrees Celsius. Taken together, the findings link temperature-dependent rhinovirus replication with host immune defense. So, yep, that wintry air, it seems, could be lowering our resistance against the common cold virus.