IL-17A produced by αß T cells drives airway hyper-responsiveness in mice and enhances mouse and human airway smooth muscle contraction.

Emerging evidence suggests that the T helper 17 (T(H)17) subset of αß T cells contributes to the development of allergic asthma. In this study, we found that mice lacking the αvß8 integrin on dendritic cells did not generate T(H)17 cells in the lung and were protected from airway hyper-responsiveness in response to house dust mite and ovalbumin sensitization and challenge. Because loss of T(H)17 cells inhibited airway narrowing without any obvious effects on airway inflammation or epithelial morphology, we examined the direct effects of T(H)17 cytokines on mouse and human airway smooth muscle function. Interleukin-17A (IL-17A), but not IL-17F or IL-22, enhanced contractile force generation of airway smooth muscle through an IL-17 receptor A (IL-17RA)-IL-17RC, nuclear factor κ light-chain enhancer of activated B cells (NF-κB)-ras homolog gene family, member A (RhoA)-Rho-associated coiled-coil containing protein kinase 2 (ROCK2) signaling cascade. Mice lacking integrin αvß8 on dendritic cells showed impaired activation of this pathway after ovalbumin sensitization and challenge, and the diminished contraction of the tracheal rings in these mice was reversed by IL-17A. These data indicate that the IL-17A produced by T(H)17 cells contributes to allergen-induced airway hyper-responsiveness through direct effects on airway smooth muscle.

The αvß6 integrin modulates airway hyperresponsiveness in mice by regulating intraepithelial mast cells.

Allergic asthma is the most common form of asthma, affecting more than 10 million Americans. Although it is clear that mast cells have a key role in the pathogenesis of allergic asthma, the mechanisms by which they regulate airway narrowing in vivo remain to be elucidated. Here we report that mice lacking αvß6 integrin are protected from exaggerated airway narrowing in a model of allergic asthma. Expression microarrays of the airway epithelium revealed mast cell proteases among the most prominent differentially expressed genes, with expression of mouse mast cell protease 1 (mMCP-1) induced by allergen challenge in WT mice and expression of mMCP-4, -5, and -6 increased at baseline in ß6-deficient mice. These findings were most likely explained by loss of TGF-ß activation, since the epithelial integrin αvß6 is a critical activator of latent TGF-ß, and in vitro-differentiated mast cells showed TGF-ß-dependent expression of mMCP-1 and suppression of mMCP-4 and -6. In vitro, mMCP-1 increased contractility of murine tracheal rings, an effect that depended on intact airway epithelium, whereas mMCP-4 inhibited IL-13-induced epithelial-independent enhancement of contractility. These results suggest that intraepithelial activation of TGF-ß by the αvß6 integrin regulates airway responsiveness by modulating mast cell protease expression and that these proteases and their proteolytic substrates could be novel targets for improved treatment of allergic asthma.

Role of integrin alphav beta6 in acute lung injury induced by Pseudomonas aeruginosa.

Deletion of integrin alphav beta6 has been associated with significant protection in experiments where lung injury was induced by bleomycin, lipophilic polysaccharides, and high tidal volume ventilation. This has led to the suggestion that antibody blockade of this integrin is a novel therapy for acute lung injury. We questioned whether beta6 gene deletion would also protect against Pseudomonas aeruginosa-induced acute lung injury. Wild-type and littermate beta6-null mice, as well as recombinant soluble TGF-beta receptor type II-Fc (rsTGF-betaRII-Fc) and anti-alphav beta6 treated wild-type mice, were instilled with live P. aeruginosa. Four or 8 h after bacterial instillation, the mice were euthanized, and either bronchoalveolar lavage fluid or lung homogenates were obtained. Deletion of the beta6 gene resulted in an overall increase in inflammatory cells in the lungs. Bacterial numbers from the lung homogenates of infected beta6-null mice were significantly decreased compared to the numbers in the wild-type mice (1.6 x 10(6) CFU versus 4.2 x 10(6) CFU [P < 0.01]). There were no significant differences in P. aeruginosa-mediated increases in lung endothelial permeability between wild-type and beta6-null mice. Similarly, pretreatment with the alphav beta6 antibody or with rsTGF-betaRII-Fc did not significantly affect the P. aeruginosa-induced lung injury or rate of survival compared to pretreatment with control immunoglobulin G. We conclude that deletion or inhibition of the integrin alphav beta6 did not protect animals from P. aeruginosa-induced lung injury. However, these therapies also did not increase the lung injury, suggesting that host defense was not compromised by this promising new therapy.

Loss of integrin alpha(v)beta8 on dendritic cells causes autoimmunity and colitis in mice.

The cytokine transforming growth factor-beta (TGF-beta) is an important negative regulator of adaptive immunity. TGF-beta is secreted by cells as an inactive precursor that must be activated to exert biological effects, but the mechanisms that regulate TGF-beta activation and function in the immune system are poorly understood. Here we show that conditional loss of the TGF-beta-activating integrin alpha(v)beta8 on leukocytes causes severe inflammatory bowel disease and age-related autoimmunity in mice. This autoimmune phenotype is largely due to lack of alpha(v)beta8 on dendritic cells, as mice lacking alpha(v)beta8 principally on dendritic cells develop identical immunological abnormalities as mice lacking alpha(v)beta8 on all leukocytes, whereas mice lacking alpha(v)beta8 on T cells alone are phenotypically normal. We further show that dendritic cells lacking alpha(v)beta8 fail to induce regulatory T cells (T(R) cells) in vitro, an effect that depends on TGF-beta activity. Furthermore, mice lacking alpha(v)beta8 on dendritic cells have reduced proportions of T(R) cells in colonic tissue. These results suggest that alpha(v)beta8-mediated TGF-beta activation by dendritic cells is essential for preventing immune dysfunction that results in inflammatory bowel disease and autoimmunity, effects that are due, at least in part, to the ability of alpha(v)beta8 on dendritic cells to induce and/or maintain tissue T(R) cells.

Aspergillus antigen induces robust Th2 cytokine production, inflammation, airway hyperreactivity and fibrosis in the absence of MCP-1 or CCR2.

BACKGROUND: Asthma is characterized by type 2 T-helper cell (Th2) inflammation, goblet cell hyperplasia, airway hyperreactivity, and airway fibrosis. Monocyte chemoattractant protein-1 (MCP-1 or CCL2) and its receptor, CCR2, have been shown to play important roles in the development of Th2 inflammation. CCR2-deficient mice have been found to have altered inflammatory and physiologic responses in some models of experimental allergic asthma, but the role of CCR2 in contributing to inflammation and airway hyperreactivity appears to vary considerably between models. Furthermore, MCP-1-deficient mice have not previously been studied in models of experimental allergic asthma. METHODS: To test whether MCP-1 and CCR2 are each required for the development of experimental allergic asthma, we applied an Aspergillus antigen-induced model of Th2 cytokine-driven allergic asthma associated with airway fibrosis to mice deficient in either MCP-1 or CCR2. Previous studies with live Aspergillus conidia instilled into the lung revealed that MCP-1 and CCR2 play a role in anti-fungal responses; in contrast, we used a non-viable Aspergillus antigen preparation known to induce a robust eosinophilic inflammatory response. RESULTS: We found that wild-type C57BL/6 mice developed eosinophilic airway inflammation, goblet cell hyperplasia, airway hyperreactivity, elevations in serum IgE, and airway fibrosis in response to airway challenge with Aspergillus antigen. Surprisingly, mice deficient in either MCP-1 or CCR2 had responses to Aspergillus antigen similar to those seen in wild-type mice, including production of Th2 cytokines. CONCLUSION: We conclude that robust Th2-mediated lung pathology can occur even in the complete absence of MCP-1 or CCR2.