2’-FL and cross-feeding bifidobacteria reshaped the gut microbiota of infants with atopic dermatitis ex vivo and prevented dermatitis in mice post-microbiota transplantation through retinol metabolism activation

2'-Fucosyllactose (2'-FL), a predominant human milk oligosaccharide, plays a crucial role in the development of the infant gut microbiota and immune system. However, the microbiota of infants with atopic dermatitis (AD) often has difficulty utilizing 2'-FL. Here, we found that strains from human milk, <i>Bifidobacterium bifidum</i> FN120 and <i>Bifidobacterium longum</i> subsp. <i>longum</i> FN103, utilized 2'-FL for growth by cross-feeding. Through an <i>ex vivo</i> continuous fermentation system, we found that 2'-FL and cross-feeding bifidobacteria synergistically enhanced the production of short-chain fatty acids (SCFAs), particularly acetate and propionate, while reshaping the gut microbiota in infants with AD. The reshaped microbiota was then transplanted into oxazolone-induced mice. We observed that AD symptoms in mice were effectively prevented, with significant changes in the ileum microbiota and increased intestinal SCFA levels. RNA sequencing analysis of Peyer's patches in the small intestine revealed activation of the retinol metabolic pathway. Nontargeted metabolomics analysis revealed a significant increase in plasma retinoate levels, which correlated markedly with AD-related markers. Collectively, our study demonstrated that supplementation with cross-feeding bifidobacteria and 2'-FL reshaped the gut microbiota, activated retinol metabolic pathways, promoted immune tolerance, and thereby prevented AD. Our findings provide novel insights into the therapeutic potential of combining prebiotics and probiotics to modulate the gut - skin axis and support immune tolerance in early life, offering a promising strategy for infantile AD management and prevention.