IL-25 (IL-17E) is a T-helper cell type 2 (Th2) cytokine best described as a potentiator of Th2 memory responses. Reports of expression of its receptor, IL-25R, on airways structural cells suggest a wider role for IL-25 in remodeling. We hypothesized that IL-25 stimulates local angiogenesis in the asthmatic bronchial mucosa. Immunoreactive IL-25 + , IL-25R + , and CD31 + (endothelial) cells in sections of bronchial biopsies from asthmatics and controls were detected by immunohistochemistry. The effect of IL-25 on angiogenesis was examined using an in vitro assay. Real-time PCR was used to detect expression of IL-25R and VEGF mRNA in cultured human vascular endothelial cells (HUVEC), and a cell proliferation kit (WST-8) was used to measure the effect of IL-25 on HUVEC proliferation. Immunostaining showed that IL-25 + , IL-25R + , and CD31 + /IL-25R + cells were significantly elevated in the bronchial mucosa of asthmatics compared with controls (P < 0.003). In asthmatics, the numbers of IL-25 + cells correlated inversely with the forced expiratory volume in 1 s (r = −0.639; P = 0.01). In vitro, HUVEC constitutively expressed IL-25R, which was up-regulated further by TNF-α. IL-25 and TNF-α also increased expression of VEGF and VEGF receptors. IL-25 increased HUVEC proliferation and the number, length, and area of microvessel structures in a concentration-dependent manner in vitro. VEGF blockade, the PI3K-specific inhibitor LY294002, and the MAPK/ERK1/2 (MEK1/2)-specific inhibitor U0126 all markedly attenuated IL-25-induced angiogenesis, and the inhibitors also reduced IL-25-induced proliferation and VEGF expression. Our findings suggest that IL-25 is elevated in asthma and contributes to angiogenesis, at least partly by increasing endothelial cell VEGF/VEGF receptor expression through PI3K/Akt and Erk/MAPK pathways.

Our data support the hypothesis that IL-25 contributes to elevated bFGF in asthmatic airways by acting on the endothelial cell IL-17RB receptor through PI3K-signalling pathways. Targeting the pathways might benefit therapy of airways remodelling.

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Bactericidal/permeability increasing (BPI) is an antibiotic protein which kills Gram-negative bacteria and neutralizes endotoxin. We have previously developed a recombinant adeno-associated virus which contains human BPI amino acid residues 1-199 and Fc fragment of human IgG1 gene (AAV-hBPI-Fc) and shown that the recombinant virus can protect mice from lethal endotoxemia. However, whether AAV-hBPI-Fc can be used in vivo for the long term remains unclear. To address this, we established an adeno-associated virus-containing mouse BPI and Fc fragment genes (muBPI-Fc) and compared antigenicity of these recombinant proteins in murine models. Immunohistochemistry showed the expression of both fusion proteins at injected sites. ELISA and Western blotting showed that the muBPI-Fc protein was detected in serum up to 8 weeks after injection, without generation of autoantibodies against muBPI-Fc. In contrast, expressed hBPI-Fc protein was only detected on the 2nd week, whereas the autoantibody against hBPI-Fc protein occurred in serum from the 4th week to the end of study. muBPI-Fc also reduced production of proinflammatory cytokines and protected mice from endotoxemia and bacteremia. Our data showed that AAV-muBPI-Fc has potential long-term efficacy as an anti-endotoxin and has anti-bacterial activity in mice, suggesting the potential clinical application of AAV-hBPI-Fc, such as in endotoxin shock.