The immunomodulatory oligonucleotide (IMO) agents containing novel RpG motif have been shown to potently modulate immune responses. Importantly, this novel motif has been shown to override species-specific receptor recognition observed with natural CpG motif. We have recently reported that second-generation IMOs containing a different stimulatory motif, CpR (R=2'-deoxy-7-deazaguanosine), effectively prevent key parameters of allergic asthma. Since most asthmatics are treated after the development of asthma, in the present study we examined whether the IMOs containing novel RpG motif can reverse established allergic airway inflammation. Mice sensitized and challenged with ovalbumin (OVA) were evaluated for airway hyperresponsiveness (AHR) to methacholine. Following this, sensitized mice were randomized and treated with placebo or two doses (30 μg and 60 μg/dose, s.c.) of RpG IMO during the following 10 days. Two days after the final treatment, mice were rechallenged with OVA and pulmonary functions were recorded. Mice treated with RpG IMO were significantly protected from both early (EAR) and late (LAR) allergic response, AHR to methacholine, BAL and peribronchial eosinophilia, BAL and serum IL-5, and total serum IgE as compared to vehicle-treated OVA-sensitized and challenged animals. There was a significant increase in immature lung dendritic cells (CD11c+CD45R+) together with increase in serum IL-10 levels and significant decrease in lung DC2 type cells (CD11c+ CD11b+CD8⍺-) following treatment with RpG IMO. These data suggest that the second-generation IMOs containing novel RpG motif are effective and potent in attenuating established allergic airway inflammation in bronchial asthma, and this effect could be mediated via decreasing lung DC2 cells and increasing immature DCs.