Probiotic supplementation alleviates diet-induced obesity via improving gut immune homeostasis and enhancing immunoglobulin A secretion.

Obesity is a metabolic disorder linked to chronic low-grade inflammation and gut microbiota imbalance, with gut-immune interactions playing a key role, making microbiota-targeted dietary interventions a promising strategy. This study selected three common probiotics-Lactobacillus bulgaricus, Lactobacillus rhamnosus, and Bifidobacterium longum-to systematically investigate their anti-obesity effects and impact on intestinal immune homeostasis in high-fat diet-induced obese mice. The results showed that all three strains significantly reduced body weight gain and adipose tissue inflammation, suppressed Ccl2 expression in adipose tissue, and markedly enhanced intestinal immunoglobulin A (IgA) secretion along with the upregulation of related signaling genes such as Tgfb1, Tnfsf13, and Cd40. Moreover, probiotics enriched immune-supporting bacteria and suppressed pro-inflammatory taxa, restoring gut balance and reducing inflammation. In mice fed a normal diet, these probiotics also increased the proportion of IgA+ cells in the intestine and Peyer's patches, as well as fecal IgA levels, suggesting a generalizable role in promoting IgA secretion. Furthermore, ex vivo intestinal culture experiments revealed that both inactivated bacterial cells and their culture supernatants stimulated IgA secretion, indicating that the immunomodulatory effects of probiotics are not solely dependent on bacterial viability. This study reveals that probiotics alleviate obesity-related immune imbalance by modulating gut microbiota and inflammation, while also enhancing mucosal immunity and intestinal homeostasis in healthy hosts. These findings expand the potential application of probiotics in the food sector and offer a theoretical basis for developing innovative functional foods based on non-viable bacterial components.