Induction of oral tolerance (OT) has been known to prevent allergic inflammation in acute asthma model within 4 weeks. However it is remained whether induction of OT may effectively prevent allergic inflammation in chronic asthma model over 4 weeks. We observed the effect of induction of OT on allergic inflammation and airway remodeling in chronic asthma model up to 8 weeks.

5-week-old female BALB/c mice divided into 4 groups-control group, asthma group, low dose OT group, and high dose OT group. To induce oral tolerance mice were fed ovalbumin (OVA) before sensitization with OVA and aluminum hydroxide-1 mg for 6 consecutive days in the low dose OT group and 25 mg once in the high dose OT group. Mice in the asthma group were fed phosphate buffered saline instead of OVA. After sensitization followed by repeated challenge with aerosolized 1% OVA during 6 weeks, enhanced pause (Penh), inflammatory cells, IL-13, and IFN-γ levels in bronchoalveolar lavage (BAL) fluids as well as OVA-specific IgE, IgG1, and IgG2a levels in serum were measured. In addition the degree of goblet cell hyperplasia and peribronchial fibrosis were observed from lung tissues by PAS and Masson's trichrome stain.

Both OT groups showed a significant decrease in Penh, inflammatory cells, IL-13, and IFN-γ levels in BAL fluids as well as OVA-specific IgE, IgG1, and IgG2a levels in serum compared with the asthma group (P<0.05). In addition, the degree of goblet cell hyperplasia and peribronchial fibrosis were significantly attenuated in both OT groups compared with the asthma group (P<0.01).

These results suggest that induction of OT may effectively prevent allergic inflammation as well as airway remodeling even in chronic asthma model up to 8 weeks.