low levels compared with AAD model group (p,0.05 or p,0.01). In contrast with Th2 cytokines IL-4, levels of Th1 cytokines IFN-c and IL-2, particularly IFN-c, were significantly higher in mice neonatally infected 108 CFU E. coli than that in AAD model group (p,0.05 for IFN-c in NALF, p,0.01 for IFN-c in BALF, and p,0.05 for IL-2 in BALF), along with the increase in groups of mice infected with 106 CFU or during adults though not so significant (p,0.05 for IFN-c in both NALF and BALF of (108infA +OVA) group). Immune response of E. coli to AAD was likewise observed on levels of IL-10, which is abundantly secreted by Tregs to mediate immune suppression, and also a pleiotropic cytokine released by Th1 and Th2 cells as w.S of Serum OVAspecific IgEAlthough serum 1516647 IgE level alone did not entirely reflect the allergic state and the clinical symptoms, it was apparent that a raised level of IgE represented the Th2 immune response and helped aid the diagnosis of allergic disease [5]. Hence we analyzed OVA-specific IgE levels in the serum prepared from blood 24 h after the final challenge. Study showed that levels of serum OVA-specific IgE were significantly higher in AAD model group than that in the control group (p,0.01) (Fig. 6). However, oral E. coli administration markedly suppressed the circulating IgE levels. Furthermore, our study also revealed that the neonatal infection with 108 CFU E. coli significantly decreased more OVA-specific IgE levels, in contrast to oral E. coli administration with 106 CFU dose or during adult period (both p,0.01), which was a coincidence with the results of histological analysis.E. coli Administration Ameliorates OVA-induced Upper and Lower Allergic Airway InflammationFurthermore, we qualitatively and quantitatively examined the alteration of allergic airway inflammation by histological analysis of eosinophil inflammation and goblet cell metaplasia in the nasal mucosa and lung. As shown in Fig. 4 and Fig. 5, there were no changes in the control group. However, there was a significant suppression ofFigure 2. The changes of allergic symptoms. The control group showed no or less allergic symptoms, whereas AAD model group had remarkable frequency of nasal rubbing and sneezing. Nevertheless, the frequency was noticeably decreased by E. coli infection. Data is shown by box and whisker plots, with whisker ends indicating minimal and maximal values and horizontal 11967625 bars representing medians, n = 10. *p,0.05, **p,0.01 as conducted. doi:10.1371/journal.pone.0059174.gEscherichia coli on Allergic Airway InflammationFigure 3. Absolute numbers of inflammation cells in 1.2 ml of NALF and BALF at 24 h after final challenge. Original magnification was 6400 (A, B). Total inflammation cells and eosinophils in 
NALF (C) and BALF (D) were significantly inhibited by E. coli infection in AAD mice model. Each bar represents the mean cell number 6 standard error of the mean (SEM), n = 10. *p,0.05, **p,0.01 as conducted. doi:10.1371/journal.pone.0059174.gE. coli Administration Alters Cytokine Production in both NALF and BALFTo further investigate the skewing of Th2-specific immune responses conferred by oral E. coli, we measured cytokines IL-4, IFN-c, IL-2 and IL-10 levels in both NALF and BALF (Fig. 7). NALF and BALF from AAD model group both contained obviously detectable levels of Th2 cytokines IL-4 compared with the control group (p,0.01), while E. coli treatment groups, especially mice neonatally infected with 108 CFU, contained relative low levels compared with AAD model group (p,0.05 or p,0.01). In contrast with Th2 cytokines IL-4, levels of Th1 cytokines IFN-c and IL-2, particularly IFN-c, were significantly higher in mice neonatally infected 108 CFU E. coli than that in AAD model group (p,0.05 for IFN-c in NALF, p,0.01 for IFN-c in BALF, and p,0.05 for IL-2 in BALF), along with the increase in groups of mice infected with 106 CFU or during adults though not so significant (p,0.05 for IFN-c in both NALF and BALF of (108infA +OVA) group). Immune response of E. coli to AAD was likewise observed on levels of IL-10, which is abundantly secreted by Tregs to mediate immune suppression, and also a pleiotropic cytokine released by Th1 and Th2 cells as w.