Short-chain fatty acids mediate interactions between immune responses and commensal bacteria in high altitude yaks

The complex interplay between host and commensal gut microbiota affects the major biological functions such as metabolism and stress adaptation, and displays pronounced seasonality in mammals. However, the seasonal dynamic patterns of immune responses and microbiota, and their interactions remain uncertain in animals inhabiting extreme environments. We analyzed monthly hormones, immunoglobulins and fecal microbiota from yaks grazing on the Tibetan plateau. Clear seasonal patterns were observed: glucocorticoid levels peaked in the cold season, while concentrations of IgA, IgG, IgM, and short-chain fatty acids (SCFAs) increased during the warm season. Yak fecal microbiota also fluctuated seasonally, with lowest diversity in the warm season but accompanied by an enrichment of Firmicutes and Actinobacteria. Taxa such as Alistipes, Bacteroides, Romboutsia and Arthrobacter contributed to seasonal shifts in the levels of SCFAs and immunoglobulins. These results indicate that yaks synchronize peak immune activation and energy production with the nutrient-rich warm season, suggesting a role for microbiome plasticity in driving immune flexibility for high-altitude animals.