Big discoveries in little things. That seems to characterize our learnings about the importance of the human microbiome. Our developing understanding of microbes and their role in health and disease has led to a nation-wide wake up call for more responsible use of antibiotics in livestock farming and medical practice. We’re beginning to understand the role of bacteria in systemic immunity, digestion, nutrient absorption, inflammation, autoimmunity, hormone metabolism, and neurotransmitters. We’re expanding our awareness by examining the human virome and the role of beneficial viruses.
And now, researchers are now beginning to look at the human mycobiome. The relationship between humans and their resident fungal species has been a neglected field of study. We’re familiar with genuses like Candida, Cryptococcus, and Aspergillus. But there are many, many species of fungi living in our lungs, digestive tracts, oral cavities, and skin that are just starting to be characterized. These likely play a big role in health and disease and highly influenced by our own immune responses. I suggest this is another pathway by which medicinal mushrooms work in the body.
Research has been limited in this area because of methodological restrictions. Typically, when studying fungi and testing for the presence of certain species, a sample is collected and transferred to flasks of sterile liquid media. The fungi is then cultured and visually examined. This technique dates back to the 1920’s. But we’re now understanding that not all fungi culture out, and many organisms have been missed.
With culture-independent methods (including DNA sequencing), we’re disovering that there are many more species than predicted, and different mycobiota patterns are associated with certain disease states, especially IBD and cystic fibrosis. Mycobiome fungi can have a commensal (mutualistic/coevolutionary) relationship with its host, or pathogenic. It’s largely dependent on context–other microbes present, the host immune response. And the mycobiome influences bacterial microorganisms. It’s a 2-way street.
When it comes to pathogenic fungi, like Candida and Aspergillus species, deficiencies in certain immune pathways are associated with greater disease risk. These pathways include Dectin-1, TLRs and Th1 responses. Interestingly, these are the exact pathways that fungal polysaccharides support and upregulate. (Fungal polysacchardies are a group of compounds that are broken down from the fungal cell wall from higher fungi like Shiitake, Reishi, Maitake, and many others.) The host immune response determines the composition of the mycobiome.
It makes me wonder: Perhaps this is an unexamined role of medicinal mushrooms–correcting some of the weakened pathways in the mycobiome. We know fungal polysacchardies (like B-glucans) increase NK cell, neutrophil, macrophage, and Th1 activity. They stimulate innate and cell-mediated immunity. But they may be interacting with the human mycobiome, and this could be another element of their role in immunity.