Various immunological phenotypes are associated with increased airway responsiveness

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Abstract
Bronchial asthma is characterized by a TH2 type immune response, chronic inflammation of the airways and increased airway responsiveness. The relationship between IgE- and inflammatory-dependent mechanisms that contribute to bronchial asthma are not well defined. The purpose of this study was to compare and analyse the immune pathways that resulted in development of allergen-induced and/or inflammatory dependent increased airways responsiveness. BALB/c and C57BL/6 mice responded to OVA-sensitization with elevated allergen-specific IgE/IgG1 serum antibody-titres and the development of cutaneous immediate-type hypersensitivity reactions. Increased airway responsiveness was observed following airway allergen challenges. However, the inflammatory component of the lung differed between the strains. In OVA-sensitized BALB/c mice a marked increase in lymphocytes, eosinophils and neutrophils in BAL fluids was parallelled with elevated production of IL-4, IL-5 and TNFα in the lung. In contrast in OVA-sensitized C57BL/6 mice, the inflammatory immune response in the lung was much weaker. We postulate that two pathways can regulate the induction of increased airway responsiveness. One depends on the presence of allergen-specific IgE/IgG1 and allergen, and a second is mediated by allergen-independent inflammation of the lung. To test this hypothesis, BALB/c mice were treated nasally with low doses of bacterial superantigen (SEB) as a prototypical inducer of airway inflammation, following which influx of lymphocytes, eosinophils and neutrophils into the airways was parallelled by development of increased airway-responsiveness in the absence of allergen-specific IgE/IgG1 antibodies and allergen. These results indicate that increased airway responsiveness is associated with different immunological phenotypes in BALB/c and C57BL/6 mice.