Epithelial Immunomodulation by Aerosolized Toll like Receptor Agonists Attenuate Allergic Responsiveness in Mice

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.