Colds are just an occasional nuisance for many folks, but some individuals seem to come down with them much more frequently. Now, NIH-funded researchers have uncovered some new clues as to why.
In their study, the researchers found that the cells that line our airways are quite adept at defending against cold-causing rhinoviruses. But there’s a tradeoff. When these cells are busy defending against tissue damage due to cigarette smoke, pollen, pollutants, and/or other airborne irritants, their ability to fend off such viruses is significantly reduced.
The new findings may open the door to better strategies for preventing the common cold, as well as other types of respiratory tract infections caused by non-flu viruses. Even small improvements in prevention could have big implications for our nation’s health and economy. Every year, Americans come down with more than 500 million colds and similar infections, leading to reduced work productivity, medical expenses, and other costs approaching $40 billion.
Over the last decade, evidence shows that people become infected with rhinoviruses much more often than they actually develop cold symptoms. That intrigued Ellen Foxman at Yale University School of Medicine, New Haven, CT. It suggested to her that the body, especially the cells in the nasal passages, must be very good at ridding us of cold viruses.
If that natural process were understood better, Foxman thought it might be possible to encourage respiratory infections to pass unnoticed even more often. Foxman already had a possible clue. Her earlier work showed that how cells respond to viral infections varies with temperature. She suspected that cells lining the cooler nasal passages must operate differently than those lining warmer airways within the lungs.
In the study published in Cell Reports, Foxman and colleagues at Yale, including first author Valia Mihaylova, cultured epithelial cells that line the nasal passages and lungs from healthy donors. They infected them with a rhinovirus or exposed them to small molecules that mimic a viral infection and watched to see how the cells would respond.
The researchers discovered the anti-viral response was stronger in the nasal cells. In contrast, cells taken from the lungs showed a stronger defense against oxidative stress, caused by reactive oxygen molecules produced in the normal course of breathing. As would be expected, lung cells must defend themselves against not only reactive oxygen but also other substances present in air laden with smoke, pollen, or other irritants.
These and other experiments suggested there is a tradeoff between defending against viral infections and other kinds of tissue damage. To take a closer look, the researchers introduced rhinovirus to cells from the nasal passages after they’d been exposed to cigarette smoke. As suspected, those cells showed a greater susceptibility to viral infection.
The findings show that the lining of our airways has effective systems in place to defend against viral infections and protect against other types of damage. But it doesn’t do so well when faced with both challenges at once. The discovery may help to explain why smokers and those with allergies or other chronic conditions tend to get more severe viral infections than other people do.
The hope is these insights will ultimately lead to strategies to improve the body’s natural defenses so that more people stay healthy even after exposure to cold viruses. For now, the best way to keep colds to a minimum is to wash your hands often, don’t smoke, and do your best to stay away from those who are sick.
Dr. Francis Collins was ppointed the 16th Director of NIH by President Barack Obama and confirmed by the Senate. He was sworn in on August 17, 2009. On June 6, 2017. President Donald Trump selected Dr. Collins to continue to serve as the NIH Director.