Intestinal Mucosa Fungus Can Affect Lung Health

The composition of the microbiome, the countless bacteria, fungi and viruses that colonize our body surface, skin, intestines or lungs, makes a decisive contribution to human health or disease. However, biological mechanisms that cause inflammations in the microbiome are still largely unknown.

Candida albicans is an opportunistic pathogenic yeast that is a common member of the human gut flora, and stimulates the immune system to produce specific defense cells, so-called Th17 cells. However, some of these Th17 cells then attack other fungi, such as Aspergillus fumigatus. This phenomenon is called cross-reactivity.

Scientists collaborating with the University of Kiel (Kiel, Germany) identified the mucocutaneous pathobiont C. albicans as the major direct inducer of human anti-fungal Th17 cells. Th17 cells directed against other fungi are induced by cross-reactivity to C. albicans. Intestinal inflammation expands total C. albicans and cross-reactive Th17 cells. Strikingly, Th17 cells cross-reactive to the airborne fungus A. fumigatus are selectively activated and expanded in patients with airway inflammation, especially during acute allergic bronchopulmonary aspergillosis.

This indicates a direct link between protective intestinal Th17 responses against C. albicans and lung inflammation caused by airborne fungi. The team identified heterologous immunity to a single, ubiquitous member of the microbiota as a central mechanism for systemic induction of human anti-fungal Th17 responses and as a potential risk factor for pulmonary inflammatory diseases.

Oliver A. Cornely, MD, FACP, FIDSA, a professor and infectious disease specialist, and co-author of the study, said, “'With this observation, we were able to show for the first time how a single member of the microbiome, Candida albicans, influences the specific immune response to a large group of other microbes. Immune cross-reactivity is probably a common mechanism by which the microbiome manipulates the immune systemwith both protective and harmful effects.” The study was published on March 7, 2019, in the journal Cell.

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