People with severe bronchiectasis have different bacteria living in their airways than do patients with mild cases of the lung disease, a new study indicates.
The findings also suggest a link between lung bacteria and altered immune responses in bronchiectasis.
The study, “Airway microbiota is associated with the severity of non‐CF bronchiectasis,” was published in The Clinical Respiratory Journal.
The human body is home to an estimated 38 trillion bacteria — going by numbers alone, there are more bacteria cells than human cells in the body. Such bacteria affect a person’s health in an abundance of ways, many of which are only beginning to be understood.
The lungs are no exception to this; emerging evidence suggests that the bacteria that reside in the lungs — collectively referred to as the lung microbiome — affect the course of respiratory diseases such as bronchiectasis. Understanding exactly how these associations work is an area of ongoing study. Scientists believe that better understanding these processes may provide more complete knowledge of how the disease develops and progresses, and could lay the groundwork for future treatment strategies.
In the new study, researchers examined the lung microbiome of 40 people — 33 women and seven men, with an average age of 58 years — with non-cystic fibrosis (CF) bronchiectasis by analyzing their sputum. In addition, blood samples were collected to measure the levels of inflammatory markers.
Of the 40 people included, 15 had mild bronchiectasis, 17 had moderate, and eight had severe disease, based on the bronchiectasis severity index.
No notable differences were seen in most inflammatory markers between the different groups. However, blood levels of prealbumin — a protein made mainly by the liver that the body uses to make other proteins — were significantly lower in people with severe bronchiectasis. Notably, low levels of this marker can be a sign of inflammation.
“To the best of our knowledge, the present study is the first report to investigate the correlation between serum prealbumin level and non-CF bronchiectasis severity,” the researchers wrote. “More investigation is needed to investigate whether serum prealbumin is an independent biomarker of non-CF bronchiectasis severity.”
In total, the scientists detected 506 different types of bacteria in the patients’ samples. Notably, 11 of these groups were only found in individuals with mild disease, whereas 16 only occurred in those with severe disease. Bacteria found in individuals with moderate disease almost fully overlapped with the other two groups.
Further statistical analyses demonstrated that, taken as a composite, the bacterial makeup in people with severe bronchiectasis was significantly different from that of people with mild disease.
The researchers then classified the samples based on what type of bacteria was most common. A total of 18 samples were determined to be Pseudomonas-dominated. Notably, Pseudomonas is a common group of bacteria that includes Pseudomonas aeruginosa, which is resistant to many medicines and increasingly resistant to available antibiotics. Nearly one-third of bronchiectasis patients are known to have chronic P. aeruginosa infections.
Compared with participants with other lung microbiome makeups, individuals with Pseudomonas-dominated microbiomes had significantly lower levels of interleukin-4 (IL-4) and transforming growth factor-beta (TGF-beta) in their blood. While IL-4 acts to dampen inflammation, TGF-beta may both boost or suppress the immune response, depending on which cells are targeted.
“These results suggest that Pseudomonas directly or indirectly affects the immune system, which may be related to the pathogenic [disease-causing] mechanism of bronchiectasis,” the researchers wrote. “To the best of our knowledge, this result is the first report of a relationship between serum TGF-[beta] level and airway microbiota.”
According to the investigators, the study’s limitations include its small sample size, the lack of comparison groups, and the fact that sputum can contain contaminants from the mouth.
“It will be important to study larger numbers of subjects for a longer time to identify the microbiome determinants that are associated with bronchiectasis severity, disease course and other clinical investigations,” they wrote.
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