Eosinophilic airway inflammation and microbiome link
medwireNews: Eosinophilic airway inflammation in patients with asthma is associated with an altered microbiome in the lower airway, report researchers.
They found that 12 steroid-free patients with asthma and low levels of eosinophils (median 1.0%) had higher α-diversity in the bronchoalveolar lavage microbiome than did 10 healthy nonasthmatic individuals. And lower β-diversity compared with both healthy individuals and 11 asthma patients with high levels of eosinophils (median 3.3%).
This means that patients with eosinophil-low asthma harbor a more diverse community of microbiota, but one that is relatively uniform across patients, the researchers explain in the Journal of Allergy and Clinical Immunology.
“The results substantiate previous findings linking asthma with microbiota diversity and suggest that microbial diversity is associated with eosinophilic airway inflammation,” they say.
There was no association, however, in asthma patients with neutrophilic airway inflammation.
Eosinophilic cationic protein activity, mannitol reactivity, sputum and bronchoalveolar lavage eosinophil counts, and fraction of exhaled nitric oxide were confirmed as variables significantly explaining the separation of microbiota.
There were 14 bacterial genera with a prevalence of 100% that differed significantly between healthy individuals and patients with asthma (eosinophil-high or -low disease), eight of which differed in abundance between patients with eosinophil-low asthma and both healthy individuals and patients with eosinophil-high asthma. Only the abundance of two bacterial genera differed significantly between patients with eosinophil-high asthma and healthy individuals.
For some genera – such as Halomonas and Sphingomonas – there was a positive association with the level of eosinophilia, and for others, including Neisseria, Bacteroides, and Rothia species, there was a negative association.
Study author Asger Sverrild (Bispebjerg Hospital, Copenhagen, Denmark) and colleagues note that the gram-negative Neisseria subflava, for example, which was significantly more abundant in patients with eosinophil-low asthma than in those with eosinophil-high asthma, has previously been shown to have immunomodulatory properties and to significantly increase after rhinovirus infection.
And, in the current study, increased levels of Sphingomonas species, which was significantly more abundant in patients with eosinophil-high than eosinophil-low asthma, was associated with a greater prevalence of airway hyper-responsiveness in the former patients.
The researchers acknowledge that they “can only speculate on any causal relation between the microbiota and airway inflammation,” but they believe that “the interrelations are undoubtedly complex, with indices of bacteria being able to work in both a proinflammatory and anti-inflammatory fashion depending on the disease state of the subject and the overall microbial composition (including vira).”
The team therefore calls for “further investigation on molecular pathways involved in asthma and the relation to airway microbiota.”
By Lucy Piper
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