<em>Bifidobacterium longum</em> DPUB-15, screened by an <em>ex vivo</em> mesenteric lymph nodes cell model, alleviates allergic responses in casein-allergic Sprague-Dawley rats

Cow's milk allergy is a global health issue, and probiotic-based treatments may offer a promising therapeutic approach. Mesenteric lymph nodes (MLNs) play a crucial role in the development of food allergies. The present study aims to establish an <em>ex vivo</em> model based on rat-derived MLN cells to screen probiotic strains with potential to alleviate casein allergy and to investigate the effects in the casein-allergic rat model. The results showed that <em>ex vivo</em> screening <em>via</em> normal and casein-sensitized SD rat MLN cells identified three strains, with&nbsp;<em>Bifidobacterium longum</em>&nbsp;DPUB-15 selected as target strain demonstrating optimal probiotic properties. Subsequently, the present study demonstrated that both live and heat-killed&nbsp;<em>Bifidobacterium longum</em>&nbsp;DPUB-15 could alleviate casein allergy in rats. Notably, heat-killed <em>Bifidobacterium</em> <em>longum</em> DPUB-15 demonstrated superior effects, further downregulating IgG2a and histamine levels, improving ileal immune balance and colonic barrier function (ZO-1), and modulating intestinal microbiota by reducing the abundance of casein allergy-associated Lachnospirales_CAG-274 and increasing the abundance of <em>Paraprevotella</em>. In conclusion, this study provides an<em> ex vivo</em> model for screening anti-allergic probiotic strains and highlights <em>Bifidobacterium longum </em>DPUB-15 as a promising candidate for alleviating casein allergy, with heat-killed <em>Bifidobacterium</em> <em>longum</em> DPUB-15 showing potential for postbiotic development in allergy treatment.