The Combination of Indole-3-Carbinol and Tryptophan Provides Additive Benefits in Enhancing Innate Immunity Against Salmonella Colitis in Mice.

Salmonella spp. remains a significant global public health concern, capable of causing a spectrum of diseases. The aryl hydrocarbon receptor (AhR) is known to confer protective effects in Salmonella-induced colitis. Although indole-3-carbinol (I3C) and tryptophan (Trp) are known dietary sources of AhR ligands, their combined effects on Salmonella pathogenesis have yet to be fully characterized. We employed a well-established Salmonella colitis model using 6-8-week-old female C57BL/6 mice to evaluate the combined effects of I3C and Trp. Mice were pretreated with oral gavage of I3C (100 mg/kg/day), Trp (100 mg/kg/day), or both for seven consecutive days before infection. The I3C + Trp combination significantly alleviated clinical signs of colitis, reduced cecal mRNA expression of proinflammatory cytokines (IL-1β, IL-6, CXCL2, IL-17α), and increased expression of immune-modulating genes (IL-22, CRAMP, ATG16L1) compared to individual treatments. Immunohistochemical staining revealed decreased zonulin and claudin-2, and increased occludin, AhR, and vitamin D receptor expression in the cecal mucosa. The combination of I3C and Trp exerts additive protective effects against Salmonella-induced colitis by modulating host immune responses and enhancing epithelial barrier integrity. These results suggest dietary AhR ligands may serve as a promising complementary approach for the prevention and management of invasive salmonellosis.