Probiotic consumption alleviates atopic dermatitis-related immune responses in association with gut microbial changes: In vitro and mouse model studies

• Atopic dermatitis (AD)-alleviating effects of novel probiotic strains were evaluated. • Probiotic consumption reduced dermatitis score and improved skin barrier function. • Probiotic consumption suppressed Il9 via Th1-related signaling in the skin. • Gut bacterial changes by probiotics were associated with improved AD symptoms. This study investigates the potential of novel probiotic strains, a 1:1 mix of Bifidobacterium longum RAPO and Lactiplantibacillus plantarum LRCC5264, to alleviate atopic dermatitis (AD). In vitro, the probiotics at 1 × 10 6 CFU/mL increased anti-inflammatory (interleukin-6; IL6) and reduced pro-inflammatory (IL9) cytokine expression in LPS-stimulated RAW 264.7 cells. In an 2,4-dinitrochlorobenzene-induced AD mouse model, treatment with the probiotics (1 × 10 6 CFU/day) for eight weeks exhibited significant reductions in dermatitis score, plasma immunoglobulin E, transepidermal water loss, and mRNA expression of ceramidase in the skin. Furthermore, the probiotic consumption suppressed Il9 mRNA expression in the skin and reduced eotaxin-1, eosinophil infiltration, and epidermal thickness. Gut microbiota analysis revealed probiotic consumption increased relative abundances of Alistipes and Ruminococcaceae_uncultured , with a negative association with immune responses and skin barrier functions. These results demonstrate the potential of the probiotic strains in modulating immune responses and the gut microbiota, suggesting their role as a dietary intervention strategy for managing AD.