Fungal Microbiota in Chronic Airway Inflammatory Disease and Emerging Relationships with the Host Immune Response.
Zhang I, Pletcher SD, Goldberg AN, Barker BM, Cope EK
Front Microbiol. 2017. doi: 10.3389/fmicb.2017.02477
Microbial communities associated with host mucosal surfaces play essential and diverse roles in biological processes from metabolism to immune regulation and homeostasis. In return, host inflammatory responses can shape the microbial community by supporting the growth of some microbes while inhibiting others. Most studies of host-associated microbiota in health and disease have focused on the bacterial microbiota, despite fungal diseases incurring a substantial infectious disease burden. Because of this, relatively little is known about the importance and function of the fungal microbiota (mycobiota). Recent advances in culture-independent sequencing approaches have helped elucidate the fungal diversity, burden, and functions associated with mucosal surfaces such as the human intestinal tract, oral cavity, skin, and respiratory tract.
The respiratory tract is a complex system that is inhabited by niche-specific communities of microbes including bacteria, fungi, and viruses. These complex microbial assemblages are in constant contact with the mucosal immune system and play a critical role in airway health and immune homeostasis. Changes in the composition and diversity of airway microbiota are frequently observed in patients with chronic inflammatory diseases including chronic rhinosinusitis (CRS), cystic fibrosis, allergy, and asthma. While the bacterial microbiome of the upper and lower airways has been the focus of many recent studies, the contribution of fungal microbiota to inflammation is an emerging research interest. Within the context of allergic airway disease, fungal products are important allergens and fungi are potent inducers of inflammation. In addition, murine models have provided experimental evidence that fungal microbiota in peripheral organs, notably the gastrointestinal (GI) tract, influence pulmonary health.
In this review, the authors explore the role of the respiratory and GI microbial communities in chronic airway inflammatory disease development with a specific focus on fungal microbiome interactions with the airway immune system and fungal-bacterial interactions that likely contribute to inflammatory disease. These findings are discussed in the context of clinical and immunological features of fungal-mediated disease in CRS, allergy, and asthmatic patients. While this field is still nascent, emerging evidence suggests that dysbiotic fungal and bacterial microbiota interact to drive or exacerbate chronic airway inflammatory disease.
According to author's opinion:
The evidence for the influence of dysbiotic fungal and bacterial microbiota interactions to drive or exacerbate chronic airway inflammatory disease is compelling. These findings open up the potential for targeted manipulation of the airway or gastrointestinal tract microbiota to improve airway health and manage airway disease in patients with CRS, asthma, and cystic fibrosis, among others. Current mycobiome studies focus on comparisons in healthy vs. diseased models, but more research needs to occur to understand the interactions between fungal and bacterial communities with the host immune system in host body sites. Fungi produce diverse secondary metabolites that can affect bacteria, while bacteria can keep the mycobiome in check by producing substances that inhibit the yeast to hyphae transition of fungal pathobionts such as in C. albicans.