Antibiotic use during infancy promotes a shift in the T(H)1/T(H)2 balance toward T(H)2-dominant immunity in mice

Background: Recent epidemiologic studies indicate that antibiotic use in in fancy may be associated with an increased risk of development of atopy; how ever, its precise mechanism remains to be elucidated. Objective: The purpose of this study is to clarify whether one such antibio tic, kanamycin, affects the T(H)1/T(H)2 balance. Methods: BALB/c mice at 3 and 52 weeks of age were orally administered 600 mg/d kanamycin sulfate for 7 consecutive days. Blood samples were collected on weeks 0, 10, 18, and 26 after the cessation of kanamycin treatment, and the effect of the kanamycin treatment on the T(H)1/T(H)2 balance was evalu ated on the basis of both the in vivo antibody levels and the in vitro sple nocyte cytokine secretion pattern. Results: The administration of kanamycin increased the serum levels of tota l IgG 1 and IgE while decreasing the serum IgG2a levels. Moreover, when spl een cells were stimulated with immobilized anti-CD3 antibody in vitro, such kanamycin treatment enhanced the in vitro IL-4 secretion while reducing th e in vitro IFN-gamma secretion. The basal IL-12 p70 secretion levels of spl enic dendritic cells in the kanamycin-treated mice were lower than those In the control mice, although no significant difference was seen in IL-12 p40 levels between either group of mice. Conclusion: These results suggested that antibiotic use during infancy may indeed quantitatively disturb, qualitatively disturb, or both the intestina l microflora and thereby prevent postnatal T(H)1 cell maturation, thus resu lting in a T(H)2-polarized immune deviation.