Figure 12.

Graphical abstract. Infection with H1N1 influenza virus not only damages the lungs of mice but also causes injury to intestinal epithelial cells and crypt atrophy in the intestine. It induces dysbiosis of the intestinal microbiota, leading to decreased diversity and richness of gut microbiota, reduced abundance of Lactobacillus, and inhibition of metabolic products especially related to tryptophan metabolism pathways. This imbalance results in disrupted proportions of Treg cells and Th17 cells in the intestines, impairing intestinal mucosal immune function. Antibiotic treatment did not significantly improve these effects. However, supplementation with exogenous tryptophan or treatment with Lactobacilli significantly improved pathological damage to the lungs and intestines caused by influenza virus infection, restored the balance of Treg cells and Th17 cells, and recovered intestinal mucosal immune function.