subsp. boosts neonatal immunity: unravelling systemic defences against .

subsp. may be a useful probiotic intervention for regulating neonatal intestinal immune responses and counteracting infection. However, recent research has focused on intestinal immunity, leaving uncertainties regarding the central, peripheral, and neural immune responses in neonates. Therefore, this study investigated the role and mechanisms of subsp. in the systemic immune responses of neonatal rats following infection. Through extremely early pretreatment with subsp. (6 hours postnatal), the neonatal rat gut microbiota was effectively reshaped, especially the community. In the rats pretreated with subsp. , was less prevalent in the blood, liver, spleen, and intestines following infection. The intervention promoted T lymphocyte subset balance in the spleen and thymus and fostered neurodevelopment and neuroimmune balance in the brain. Furthermore, metabolic profiling showed a strong correlation between the metabolites in the serum and colon, supporting the view that subsp. pretreatment influences the systemic immune response by modifying the composition and metabolism of the gut microbiota. Overall, the results imply that subsp. pretreatment, through the coordinated regulation of colonic and serum metabolites, influences the systemic immune responses of neonatal rats against infection.