Abstract

Abstract Conjugated linoleic acid (CLA) is a dietary lipid that modulates host–microbiota–immune interactions, yet its mechanistic impact on mucosal defense remains unclear. Here, we show that oral CLA supplementation enhances resistance to Salmonella Typhimurium infection and is associated with coordinated changes in gut microbial composition and mucosal immune responses. CLA-enriched commensals, including Dubosiella and Lactobacillus, were associated with increased production of CLA-derived oxylipins and activation of immune surveillance genes. Functionally, CLA pretreatment reduced Salmonella colonization, preserved epithelial integrity, and decreased neutrophilic inflammation without direct antibacterial effects. Single-cell RNA sequencing of ileal intraepithelial lymphocytes revealed that CLA predominantly reprogrammed intestinal CD8⁺ T cells toward an oxidative phenotype and enhanced effector activity. ATAC-seq revealed increased chromatin accessibility at loci associated with metabolic regulation, consistent with transcriptional reprogramming toward oxidative fitness. Mechanistically, CLA directly activated PPARγ signaling to promote mitochondrial biogenesis, oxidative phosphorylation, and the production of IFN-γ and granzyme B in CD8⁺ T cells; pharmacologic inhibition of PPARγ attenuated these effects both in vitro and in vivo. Notably, depletion of CD8⁺ T cells eliminated CLA-mediated protection and abolished early restriction of bacterial dissemination at Peyer’s patches and mesenteric lymph nodes. Although CLA enhanced CD8⁺ T-cell effector programs, antibiotic depletion and fecal microbiota transplantation experiments demonstrated that an intact gut microbiota is necessary for effective protection in vivo. Together, these findings identify CLA as a dietary modulator that strengthens mucosal resistance to Salmonella by promoting PPARγ-mediated metabolic reprogramming and enhanced effector fitness in intestinal CD8⁺ T cells.