Why Do We Get More Colds in Winter? Blame Your Nose

Should we be wearing balaclavas? Scientists have finally uncovered how our noses’ immune response weakens when temperatures drop.   -   Copyright  Canva

Quick Summary:

• A new study shows that as temperatures drop, nasal cells release fewer of the tiny protectors that bind and neutralize invading germs.

• To figure out what exactly was causing this antiviral capability, the scientists then incubated the vesicles with the viruses and imaged them under a microscope.

• They incubated the TLR3-stimulated vesicles with human nasal cells exposed to three different types of viruses: a coronavirus and two rhinoviruses.

BOSTON - Cold and flu season is upon us, but germs that cause colds are in the air year-round. So, why do we seem to get sick more in winter?

We've always thought that people were more likely to get sick in the wintertime because the cold weather forces us inside where we're more likely to exchange germs. But the fault may rest instead in the nose, which is one of the first points of contact between the outside environment and inside the body.

Researchers at Harvard Medical School and Mass Eye and Ear have newly discovered an immune response inside the nose that fights off viruses responsible for upper respiratory infections, like the common cold, the flu, and COVID-19.

But reducing the temperature in the nose by as little as nine degrees cut its germ-fighting response by almost half.

So now they want to figure out how to bolster the immune response, with a nasal spray, for example, to reduce the risk of infection as temperatures drop. 

When cold weather ‘numbs’ the immune system:

Previous research from the team had found that when we breathe, cells inside our nose release tiny particles called extracellular vesicles (EVs) that swarm, bind and kill bacteria - just like hornets would swarm you if you attacked their nest.

For their latest study, the researchers set out to answer two questions: is this immune response in the nose also triggered by viruses, and do lower temperatures affect its strength?

In both cases, the answer was yes.

The scientists took nasal samples from volunteers and cultured one batch in their lab at the normal body temperature of 37C, and another batch at 32C – because that’s how low the temperature inside our noses typically drops when we’re outdoors in frigid weather.

Under normal body-heat conditions, the extracellular vesicles – the tiny “hornets” in our noses – were successfully deployed and served as “decoys” that viruses would latch onto instead of the cells they would otherwise target.

“Those extracellular vesicles actually bind to the viruses, which are suspended in the nasal mucus,” said the study’s lead author Di Huang.

In colder temperatures, on the other hand, this defence system wavered: fewer of these vesicles were produced, and they packed less punch against the winter viruses assailing them - in this case, two rhinoviruses and a coronavirus (that was not COVID-19).

Harnessing the nose’s immune response:

Previous studies have suggested common respiratory viruses thrive at lower temperatures.

In 2015, a team at Yale University found that the rhinovirus (which causes most common colds) can spread more efficiently in the cooler temperature found inside the nose than at core body temperature.

Research from the US National Institutes of Health has also shown that flu viruses are better at spreading in chilly climates.

Mansoor Amiji, a pharmaceutical sciences professor at Boston’s Northeastern University, who co-led the latest study, expects the nose’s innate response to pathogens could be tested against a wide range of viruses.

The research could pave the way to new therapeutic options harnessing the nose’s response system to fend off the common cold, or even flu and COVID-19, he added.

“Can you create artificial virus sponges – a decoy cell – that the virus can bind to? And now you have an antiviral compound that destroys it before it infects the actual cell,” he said.