Why Some People Catch a Cold and Others Don't

Whether you catch a cold this winter or make it through the season scot-free may depend in part on how many "stressors" your nose and airway passages encounter, a new study suggests.

The research looked at two defense mechanisms that cells in a person's airway use to protect themselves from threats: one that protects against viruses like the common cold virus and another that protects against "oxidative stress." This form of cell damage is triggered by viruses and other irritants, such as cigarette smoke or pollen.

The study found that there's a trade-off between these two defenses: more protection against oxidative stress damage (for example, damage induced by cigarette smoke) means less protection against invaders like rhinovirus, which is the main cause of colds. [7 Absolutely Horrible Head Infections]

"Your airway lining protects against viruses but also other harmful substances that enter airways," senior study author Dr. Ellen Foxman, an assistant professor of laboratory medicine at Yale School of Medicine in New Haven, Connecticut, said in a statement. "The airway does pretty well if it encounters one stressor at a time. But when there are two different stressors, there's a trade-off," Foxman explained. "What we found is that when your airway is trying to deal with another stress type, it can adapt, but the cost is susceptibility to rhinovirus infection."

The study was published Sept. 11 in the journal Cell Reports.

Defense "trade-off"

Respiratory viruses cause an estimated 500 million colds and 2 million hospitalizations in the United States every year, the researchers said. However, some people can be exposed to a virus without getting sick, because the cells that line their airways clear the virus before it causes symptoms. But for other people, this clearance doesn't happen, and they wind up sick.

To better understand why some people get sick from cold viruses while others escape illness, the researchers examined airway cells from healthy human donors. The cells were obtained from the lining of people's nasal passages or of their lungs.

Researchers found that the nasal cells had a stronger inherent defense response to viruses, while the lung cells had a stronger defense against oxidative stress.

Later experiments revealed that there was indeed a trade-off between these two defense mechanisms. For example, when the researchers exposed nasal cells to cigarette smoke to trigger an oxidative-stress response, the cells became more susceptible to rhinovirus.

"They survive the cigarette smoke but can't fight the virus as well," Foxman said. "And the virus grows better."

The finding might explain why cigarette smokers tend to be more susceptible to rhinovirus infection compared to people who don't smoke, the researchers said.

The results also suggest that finding ways to protect the cells lining the airway from oxidative stress "may lead to effective strategies to enhance natural defense against rhinovirus infection," the researchers concluded. However, more studies will be needed to investigate this idea.

Original article on Live Science.

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