Methods: Faecal samples were collected from infants during the first 3 months of life. Bacterial DNA was extracted from the faecal samples and Bifidobacterium longum, B. lactis, B. breve, B. angulatum, B adolescentis, and B. catenulatum were detected by real time PCR. Infants’ peripheral blood mononuclear cells at 12 months were stimulated with ovalbumin (OVA), heat-killed LGG (HKL) (the probiotic used in the original study), tetanus toxoid (TT), anti-CD3 or without stimulus. Cells were analysed by flow cytometry for markers of dendritic cells phenotype and regulatory T cell (Treg) numbers. Culture supernatants were analysed for IL-4, IL-6, IL-10, IL-13, IFN-γ and TNF-α by multiplex ELISA, while TGF-β1 and IL-12p40 were measured using ELISA.
Results: Colonisation with B. longum at day 7 of life was associated with significantly higher (p < 0.01) levels of Th1 cytokine (IFN-γ) and pro-inflammatory cytokines (IL-6 and TNF-α) and increased (p < 0.05) secretions of Th2 (IL-13) and regulatory cytokine (IL-10) in infants at 12 months. However, colonisation with B. adolescentis at day 3 was associated with higher secretion of IL-4 cytokine. A significantly increased numbers of Treg were observed in infants colonised with B. adolescentis at 7 days of age.
Conclusions: Colonisation with specific Bifidobacterium species in early life can influence cellular immune function, namely cytokine profiles and Treg later at 12 months. This suggests that probiotic treatment during pregnancy may modulate infant immune function as late as 12 months of age, feasibly mediated by modulation of infant microbiota. However, the immune mechanism that might protect against allergic disease is still unclear.