Importance of intestinal colonisation in the maturation of humoral immunity in early infancy: a prospective follow up study of healthy infants aged 0-6 months.

AIM: To evaluate the role of intestinal microflora and early formula feeding in the maturation of humoral immunity in healthy newborn infants.

STUDY DESIGN: Sixty four healthy infants were studied. Faecal colonisation with Bacteroides fragilis group, Bifidobacterium-like, and Lactobacillus-like bacteria was examined at 1, 2, and 6 months of age, and also the number of IgA-secreting, IgM-secreting, and IgG-secreting cells (detected by ELISPOT) at 0, 2, and 6 months of age.

RESULTS: Intestinal colonisation with bacteria from the B fragilis group was more closely associated with maturation of IgA-secreting and IgM-secreting cells than colonisation with the other bacterial genera studied or diet. Infants colonised with B fragilis at 1 month of age had more IgA-secreting and IgM-secreting cells/10(6) mononuclear cells at 2 months of age (geometric mean (95% confidence interval) 1393 (962 to 2018) and 754 (427 to 1332) respectively) than infants not colonised (1015 (826 to 1247) and 394 (304 to 511) respectively); p = 0.04 and p = 0.009 respectively.

CONCLUSIONS: The type of bacteria colonising the intestine of newborns and the timing may determine the immunomodulation of the naive immune system.