Activity of Lactobacillus gasseri strain LLG1 and its exopolysaccharides in an inflammatory cell model and on Candida albicans proliferation

Exopolysaccharides (EPS) are carbohydrate polymers produced by various bacteria, including species of the genus Lactobacillus. Until now, the link between the functional properties of these bacteria and their EPS remains poorly understood. Lactobacilli are used in a wide range of applications due to their protective effects against inflammation and their role in maintaining intestinal homeostasis. However, the functional properties of their EPS remain weakly characterized. This study investigated the EPS produced by Lactobacillus gasseri (Lg-EPS), a human-derived probiotic, focusing on their immunomodulatory activity and inhibitory effects on the growth and virulence of Candida albicans, an opportunistic fungal pathogen associated with dysbiosis and immune dysfunction. The results show that Lg-EPS are composed of 59.1% glucose, 26.0% galactose, 14.6% rhamnose, and 0.3% N-acetyl-glucosamine. Functionally, Lg-EPS reduced the expression of pro-inflammatory cytokines (IL-6, IL-8, CCL-2) and IL-6 protein levels, while increasing IL-10 expression and secretion. These effects were associated with downregulation of TLRs, MyD88 and NF-κB, alongside upregulation of the aryl hydrocarbon receptor (AhR), an intracellular transcription factor involved in immune modulation. Additionally, Lg-EPS increase induction of AhR activity in HT29-Lucia™ AhR cells. Furthermore, Lg-EPS inhibited C. albicans biofilm formation and fungal growth. These findings suggest that Lg-EPS contribute to immune regulation and antifungal defense via AhR activation. This receptor, known for sensing microbial metabolites, mediates anti-inflammatory effects by suppressing NF-κB signaling, enhancing IL-10 production, and reinforcing epithelial barrier function. This is the first report to demonstrate the AhR-dependent anti-inflammatory effect of bacterial EPS.