Researchers investigating the nasal microbiota of people who have asthma and allergic rhinitis found they have different fungi in their noses when compared to others. This suggests new targeted ways to treat these irritating conditions.
Allergic rhinitis is a common condition that usually involves sneezing, itching, a blocked and running nose, and inflammation of the nasal mucous membranes. This condition and asthma are the two of the most common chronic respiratory diseases experienced across Western countries. Although classified as separate conditions, they often come together, as the same substances that cause hay fever (allergic rhinitis), such as dust, pollen, and pet dander, can also cause asthma symptoms.
Anyone who experiences these conditions understands how disruptive they can be to everyday life; in fact, these two airway issues represent a considerable disease burden. Given their common coexistence, some have speculated that they may stem from a combined airway inflammatory disease.
Existing research has shown that the upper airway, especially the nasal cavity, is not a “clean” space but is actually home to bacterial communities made up of opportunistic pathogens. These microscopic critters can use this region as a place to spread from, invading other sections of the respiratory tract and contributing to the development of conditions like asthma and allergic rhinitis, as well as other respiratory illnesses.
But in recent years, scientists have become increasingly aware of the role that fungi in human microbiomes can play in our health, which has led them to be implicated in asthma onset as well. However, very few studies have examined fungi in the upper respiratory system and, so far, only one study has characterized the airway mycobiome – the community of fungi living in or on an organism – of people with allergic rhinitis. This means we are still not completely sure about what type of fungal communities live up our noses, how they interact, and what their functions are.
In this latest study, researchers examined the microbiotas of patients’ noses and found that allergic rhinitis patients, whether or not they had asthma as well, had different fungi up their noses than “healthy” people in the control groups.
“We showed that allergic rhinitis samples displayed a significantly higher fungal diversity and a different fungal community structure compared to those of healthy controls,” Dr Luís Delgado of the University of Porto, Portugal, one of the study authors, said in a statement. “This may suggest that allergic rhinitis increases the diversity and changes the composition of the upper airway’s microbiome.”
To reach this conclusion, Delgado and colleagues recruited 214 participants including children and young adults who attended an immunology and asthma clinic in Porto, Portugal. In this country, nearly a quarter of the adult population have allergies that cause running noses, so it is a big issue.
Among these participants, 155 had both allergic rhinitis and asthma, while 47 only had the former and 12 only had the latter. The team also recruited 125 healthy controls for the study.
Using nasal swabs, the scientists gathered samples from the participants’ noses and sequenced any fungal DNA they found, focusing on two specific regions to identify different fungal species and to develop a picture of each patient’s mycobiome. After they conducted quality controls, the team had gathered 306 samples they could work with.
Following this, the team used network analysis – a technique that examines the structure of systems by mapping the relationship between points, or “nodes” – to understand the relationship between different fungi. They also characterized the communities that were present in both healthy patients and in those who have allergic rhinitis, asthma, or both, and investigated their function by examining the metabolic pathways they affected. This helped them understand the implications of any variations in the types of fungi present in each group of people.
They found that the most common fungi among all samples were Ascomycota and Basidiomycota. Within these two families, 14 genera appear to dominate the mycobiomes.
“Among these dominant genera we detected common fungi that have been recognized in humans as allergenic or opportunistic pathogenic fungi,” Delgado added. “This suggests that the nasal cavity is a major reservoir for fungi that could be involved in allergic rhinitis and asthma.”
Importantly, the team found a very clear and statistically significant difference between the fungi present in patients with respiratory disease and those without. However, there was no difference between the different groups with respiratory disease. Those who had respiratory disease had more diverse and richer mycobiomes than their healthy counterparts, and samples taken from patients with both allergic rhinitis and asthma appeared to have more evidence of connections between them than the other groups. This suggests fungi may affect the nose’s immune environment.
But what does this mean for potential treatments? Well, Delgado and colleagues found three metabolic pathways associated with the production of an intermediate of purines, chemical compounds cells use to build DNA and RNA. Called AIR (5-aminoimidazole ribonucleotide), this intermediate building block is necessary for energy metabolism and DNA synthesis. So if other research can confirm the links identified here and figure out what is causing them, then AIR could be a target for future diagnosis or even treatments.
“However, we could not control all patient-specific variables, such as disease severity and related treatment levels, and patients were sampled at a single time,” Delgado added.
While the new study offers a broad picture, it doesn’t tell us how the mycobiome changes over time. More research, especially longitudinal studies, is needed to see whether fungi drive disease processes, and which are responsible for all this snot.
The paper is published in Frontiers in Microbiology.
