Allergic asthma is a chronic inflammatory respiratory disease associated with eosinophilic infiltration, increased mucus production, airway hyperresponsiveness, and airway remodeling. Epidemiologic data reveal that the prevalence of allergic sensitization and associated diseases has increased in the twentieth century. This has been hypothesized to be partly due to reduced contact with microbial organisms (the hygiene hypothesis) in industrialized society. Airway epithelial cells, once considered a static physical barrier between the body and the external world, are now widely recognized as immunologically active cells that can initiate, maintain, and restrain inflammatory responses, such as those that mediate allergic disease. Airway epithelial cells can sense allergens via expression of myriad Toll-like receptors (TLRs) and other pattern-recognition receptors. We sought to determine whether the innate immune response stimulated by a combination of Pam2CSK4 (“Pam2”, TLR2/6 ligand) and a class C oligodeoxynucleotide ODN362 (“ODN”, TLR9 ligand), when delivered together by aerosol (“Pam2ODN”), can modulate the allergic immune response to allergens. Treatment with Pam2ODN 7 days before sensitization to House Dust Mite (HDM) extract resulted in a strong reduction in eosinophilic and lymphocytic inflammation. This Pam2ODN immunomodulatory effect was also seen using Ovalbumin (OVA) and A. oryzae (Ao) mouse models. The immunomodulatory effect was observed as much as 30 days before sensitization to HDM, but ineffective just 2 days after sensitization, suggesting that Pam2ODN immunomodulation lowers the allergic responsiveness of the lung, and reduces the likelihood of inappropriate sensitization to aeroallergens. Furthermore, Pam2 and ODN cooperated synergistically suggesting that this treatment is superior to any single agonist in the setting of allergen immunotherapy.

Recent studies have linked exposure to microbes and a reduction of allergic diseases. We sought to determine whether activation of innate immunity by aerosolized Toll-like receptor (TLR) agonists could attenuate the development of allergic inflammation in mice. BALB/cJ mice were sensitized and challenged with House Dust Mite (HDM). Some mice were treated by aerosol with ligands for TLR9 (ODNm362) and TLR2/6 (Pam2CSK4) in combination (Pam2-ODN). Allergic inflammation was assessed by quantification of leukocytes in bronchoalveolar lavage fluid (BALF) and epithelial mucin content with periodic acid fluorescent Schiff stain (PAFS). Pam2-ODN-treated mice exhibited a 94% reduction in eosinophils, 90% reduction in lymphocytes, and a 44% reduction in epithelial mucin content. Lymphocyte subset analysis showed a 50% reduction in TH2 cells without a detectable change in any other TH subset. Using an alternate allergic inflammation model with Ovalbumin (OVA) Pam2-ODN-treated mice showed greater than 50% reductions in total and OVA-specific IgE serum concentrations. IgG2a concentrations, which are reduced in OVA-sensitized mice, returned to baseline with Pam2-ODN treatment. There is a stark contrast of the efficacy in mice treated before and after sensitization that suggests Pam2-ODN may modulate the tendency of sensitization when exposed to aeroallergens. Previous studies have shown that lung epithelial cells are required for Pam2-ODN lung responses, and taken together with these new data, Pam2-ODN may reprogram airway epithelial cells to be tolerogenic to aeroallergens, but additional investigation is required to understand the precise molecular mechanism of Pam2-ODN in this context.

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Allergic asthma is a chronic inflammatory respiratory disease associated with eosinophilic infiltration, increased mucus production, airway hyperresponsiveness (AHR), and airway remodeling. Epidemiologic data has revealed that the prevalence of allergic sensitization and associated diseases has increased in the twentieth century. This has been hypothesized to be partly due to reduced contact with microbial organisms (the hygiene hypothesis) in industrialized society. Airway epithelial cells, once considered a static physical barrier between the body and the external world, are now widely recognized as immunologically active cells that can initiate, maintain, and restrain inflammatory responses, such as those that mediate allergic disease. Airway epithelial cells can sense allergens via myriad expression of Toll-like receptors (TLRs) and other pattern-recognition receptors (PRRs). We sought to determine whether the innate immune response stimulated by a combination of Pam2CSK4 (“Pam2”, TLR2/6 ligand) and a class C oligodeoxynucleotide ODN362 (“ODN”, TLR9 ligand) when delivered together by aerosol (“Pam2ODN”), can modulate the allergic immune response to allergens. Treatment with Pam2ODN 7 days before sensitization to House Dust Mite (HDM) extract resulted in a strong reduction in eosinophilic and lymphocytic inflammation. This Pam2ODN immunomodulatory effect was also seen using Ovalbumin (OVA) and A. oryzae mouse models. The immunomodulatory effect was observed as much as 30 days before sensitization to HDM, but ineffective just 2 days after sensitization, suggesting that Pam2ODN mechanism of action involves immunomodulation of the response from airway epithelial cells to aeroallergens, possibly due to a repolarization of the immune response from type 2 to a type 3/type 17 direction. Furthermore, Pam2 and ODN cooperated synergistically to induce the immunomodulatory phenotype suggesting that this treatment is superior to all investigational TLR receptor agonists in the allergen immunotherapy setting which only utilize a single PRR agonist at one time. These data suggest that allergen immunotherapy using Pam2ODN might have a role in maximizing allergen immunotherapy effectiveness.

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