Small but mighty: the human mycobiome as an immunopharmacological regulator of inflammation and autoimmunity.

The human mycobiome comprising commensal fungi such as Saccharomyces, Candida, Malassezia and others constitutes less than 0.1 percent of total gut microbes yet exerts outsized influence on host immune homeostasis. Fungal cell-wall components (β-glucans, mannans, chitin) engage C-type lectin receptors (Dectin-1/2), Toll-like receptors and NOD-like receptors to initiate Syk-CARD9, NF-κB and inflammasome signaling. These pathways shape both pro-inflammatory Th17/IL-22 responses that reinforce mucosal barrier integrity and anti-inflammatory IL-10/Treg circuits that promote immunotolerance. Commensal yeasts such as Saccharomyces boulardii secrete short-chain fatty acids that expand Foxp3+ regulatory T cells and bolster mucus production, while Malassezia indoles activate the aryl hydrocarbon receptor to induce tolerogenic dendritic cells. Conversely, Candida-derived prostaglandins and oxylipins dampen Th1-mediated defenses, skewing immunity toward a regulatory phenotype. In murine models of inflammatory bowel disease, type 1 diabetes, and rheumatoid arthritis, supplementation with fungal -glucans and live yeasts indicates potential reductions in disease severity by modulating cytokine networks. Clinical studies further support these findings, with probiotic yeast administration lowering relapse rates in ulcerative colitis and Crohn's disease and improving systemic inflammation markers in multiple sclerosis. While mycobiome dysbiosis correlates with autoimmune flares, strategic restoration of fungal balance offers a novel avenue for therapeutic intervention. Collectively, current research underscores the mycobiome's integral role in immune regulation and highlight fungal metabolites and cell-wall ligands as promising targets for the prevention and treatment of autoimmune diseases.