Hair-like structures that clear mucus found abnormal in cystic fibrosis
Such alterations could contribute to mucus accumulation, lung infections
Cilia, the structures on the surface of respiratory cells that help propel mucus out of the airways, have altered movement patterns in people with cystic fibrosis (CF), a study from Belgium found.
The researchers believe these abnormalities likely stem from inflammation and contribute to impaired mucociliary clearance (MCC) in CF patients.
MCC is a natural defense system of the lungs wherein mucus traps pathogens, or disease-causing organisms, and other small particles that have invaded the airways in order to remove them.
Impaired MCC can contribute to mucus accumulation in the airways and to serious lung infections.
The study, “Evidence for secondary ciliary dyskinesia in patients with cystic fibrosis,” was published in the Journal of Cystic Fibrosis.
Identifying causes of impaired mucus clearance in cystic fibrosis
In CF, thick and sticky mucus accumulates throughout the body. The airways are particularly affected, leaving patients prone to chronic respiratory infections and declining lung function.
Epithelial cells lining the respiratory tract are what push the mucus in the right direction. They do this via tiny hair-like structures called cilia that reside on their surface. Cilia move in a coordinated, wave-like fashion to propel the mucus to the throat, where it can be coughed up or swallowed.
MCC, which is known to be impaired in CF, may arise from problems with the mucus, but also from dysfunction of the cilia, called ciliary dyskinesia.
Ciliary dyskinesia can involve an abnormal beat frequency, where the cilia beat at a slower or faster rate than normal, as well as an abnormal beat pattern, where the type of movement they make is atypical.
It can also be primary — due to innate defects in the cilia — or secondary, arising as a result of things like infection or inflammation in their environment.
In the study, the scientists aimed to more closely examine the characteristics of ciliary dyskinesia in CF. They collected epithelial cells covered in cilia from the nasal passages of 51 CF patients — 28 children and 23 adults — as well as 30 healthy people, and examined how they moved under a microscope.
Scientists believe ciliary dyskinesia in CF is likely secondary to inflammation
Overall, the researchers found evidence of ciliary dyskinesia in the CF patient cells. The CF cilia beat significantly more slowly than the healthy ones, and there was a higher proportion of cilia with an abnormal beat pattern in CF cells.
Similar observations were made when looking specifically at the pediatric patients.
In adults with CF, ciliary beat frequency was not altered, but a higher proportion of cells with an abnormal beat pattern was still observed.
To distinguish whether the ciliary dyskinesia was primary or secondary, the scientists took additional collected cells and grew them in an air-liquid interface cell culture, which mimics the environment of the epithelial cells in the respiratory tract.
Essentially, the idea is that if ciliary dyskinesia is innate (primary), the observed alterations would persist no matter what. But if it was secondary to something like inflammation or infection in the patients’ bodies, the changes would go away when the scientists grew the cilia in the new cell culture environment.
The results showed that the earlier observed ciliary dyskinesia was no longer present after this process, indicating that ciliary dyskinesia in CF is secondary.
In conclusion, we showed that an abnormal ciliary beating is present in CF patients from childhood, and that this ciliary dyskinesia is not innate.
The only clinical factor associated with ciliary dyskinesia was nasal polyps, a type of painless growth in the nasal cavities. The absence of such polyps was associated with a lower proportion of cilia with abnormal beat patterns. In their analysis, the team found that chronic airway infections were not linked to ciliary dyskinesia.
“In conclusion, we showed that an abnormal ciliary beating is present in CF patients from childhood, and that this ciliary dyskinesia is not innate,” the researchers wrote.
The team believes that these cilia alterations in CF likely arise secondarily to inflammation, but this will need to be established in future studies.
Ultimately, ciliary dyskinesia could contribute to the known problems with MCC that are observed in CF.
“Studies evaluating MCC in parallel with ciliary beating might confirm this hypothesis, and, in the future, new treatment strategies could target ciliary beating, which might improve MCC,” the team concluded.
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