Bifidobacteria infantis and human milk oligosaccharides have independent and synergistic effects on immune response and amino acid metabolism in germ-free mouse models

ABSTRACT Early-life microbial colonization is essential for gut and immune development. Human milk oligosaccharides (HMOs) support the growth of Bifidobacterium infantis (BI). Here, we studied the individual and combined effects of BI and HMOs on the immune and colon transcriptomes and on serum and cecal metabolome. Germ-free mice were randomly assigned to four groups (10–14/group: HMO, BI, BI + HMO, and control no HMO or BI). HMO and BI + HMO groups received 5 mg/day each of 2′-fucosyllactose, lacto-N-tetraose, and 3′-sialyllactose for 14 days. BI and BI + HMO received BI ATCC 15,697 (1 × 10 9 CFU/day) on days 1, 4, and 9. Mono-colonization with BI increased monocytes, macrophages, B cells, CD4 + T cells, and Treg cells in mesenteric lymph nodes (MLN) relative to controls. In the spleen, BI alone increased B cells, dendritic cells, Th17 cells, and ILC3 cells, and enriched serum amino acid metabolism pathways. Additionally, BI influenced colonocyte gene expression and modulated serum metabolites that regulate circadian rhythms. BI + HMO increased MLN Th17 cells and spleen monocytes compared with HMO alone. Collectively, the results of this study highlight the complex interplay among host-microbe-diet interactions and emphasize the importance of considering these interactions when designing strategies to modulate infant health during early life. IMPORTANCE Early life immune and gut microbiome development are shaped by human milk (HM). One of the most important drivers of these processes is the human milk oligosaccharides (HMOs). Bifidobacterium infantis (BI) possesses a unique enzymatic system that enables efficient HMO uptake and intracellular metabolism, providing a competitive advantage over other microbial species in the breastfed infant gut. To date, the potential direct and synergistic effects of BI and HMO have not been fully explored. The knowledge generated herein identified the independent and synergistic effects of HMOs and BI on gut immune response, serum and cecal metabolites, and colonic gene expression.