Reciprocal expression of IL-25 and IL-17A is important for allergic airways hyperreactivity.

BACKGROUND: Interleukin (IL)-25 (IL-17E) is a potent inducer of the type-2 immune effector response. Previously we have demonstrated that a neutralizing anti-IL-25 antibody, given during the establishment of ovalbumin-specific lung allergy, abrogates airways hyperreactivity. OBJECTIVE: Blocking IL-25 results in the suppression of IL-13, a cytokine known to exacerbate pulmonary inflammation, and an unexpected reciprocal increase in IL-17A. The role of IL-17A in asthma is complex with reports of both pro-inflammatory and anti-inflammatory functions. Our aim was to determine the influence of IL-17A in regulating IL-25-dependent lung allergy. METHOD: Neutralizing antibodies to IL-25 and/or IL-17A were administered during an experimental model of allergic asthma. Bronchoalveolar cell infiltrates and lung cytokine production were determined to assess lung inflammation. Invasive plethysmography was undertaken to measure lung function. RESULTS: Neutralization of IL-25 correlated with a decrease in IL-13 levels and an increase in IL-17A production, and an accompanying prevention of airway hyperresponsiveness (AHR). Notably, the blocking of IL-17A reversed the protective effects of treating with anti-IL-25 antibodies, resulting in the re-expression of several facets of the lung inflammatory response, including IL-13 and eotaxin production, eosinophilia and AHR. Using mice over-expressing IL-13 we demonstrate that treatment of these mice with anti-IL-25 fails to suppress IL-13 levels and in turn IL-17A levels remain suppressed. CONCLUSIONS AND CLINICAL RELEVANCE: IL-13 is known to be an important inducer of lung inflammation, causing goblet cell hyperplasia and promoting airways hyperreactivity. Our data now demonstrate that IL-13 also plays an important role in the genesis of lung inflammation downstream of IL-25 by suppressing a protective IL-17A response. These findings also highlight the important reciprocal interplay of the IL-17 family members, IL-25 and IL-17A, in regulating allergic lung responses and suggest that the balance of IL-17A, together with IL-25, will be an important consideration in the treatment of allergic asthma.

Tim1 and Tim3 are not essential for experimental allergic asthma.

BACKGROUND: Initial studies suggested that polymorphisms in Tim1 and Tim3 contribute to the development of airway hyperreactivity (AHR) in an acute mouse model of asthma. This was also mirrored in human genetic studies where polymorphisms in Tim1 and Tim3 have been associated with atopic populations. OBJECTIVE: Further studies using anti-Tim1 or -Tim3 antibodies, or Tim fusion proteins, have also suggested that these molecules may function as regulators of type-1 and type-2 immunity. However, their role in the development of AHR and airway inflammation remains unclear. Given the proposed roles for Tim1 and Tim3 in type-1 and type-2 responses, we sought to determine whether these molecules were important in regulating antigen-driven lung allergy and inflammation. METHOD: We used Tim1- and Tim3-deficient mice and determined how the development of allergic lung inflammation was affected. RESULTS: AHR was induced normally in the absence of both Tim1 and Tim3, although Tim1-deficient mice did show a small but significant decrease in cell infiltration in the lung and blood eosinophilia. Although Tim3 was expressed on CD4(+) T cells in the allergic lung, Tim1 expression was restricted to CD86(+) B cells. CONCLUSIONS AND CLINICAL RELEVANCE: Thus, Tim1 and Tim3 are not essential for the induction of the type-2 response in lung allergy. This is contrary to what was proposed in a number of other studies using neutralizing and activating antibodies and questions the clinical relevance of Tim1 and Tim3 for novel allergy therapies.