| Asthma is one of the most common illnesses that seriously endanger human health, and its morbidity and mortality are increasing worldwide in the recent decade. The prevalence of asthma in China is also becoming more and more severe, especially in children. Therefore, it is urgently required to investigate asthma pathogenesis in depth, especially the molecular mechanism of chronic asthmatic responses such as airway remodeling, and to develop new therapeutic targets and strategies for clinically intervening the disease process of asthma.TGF-P is considerd to be tightly associated with the occurrence and development of asthma. On the one hand, TGF-β is involved in the process of inflamamtory responses, and can excert both anti- and pro- inflammation effects. On the other hand, TGF-β plays a pivotal role in tissue remodeling such as fibrogenesis. Clinical studies have associated gene polymorphism of TGF-β isoforms with asthma susceptibility, and showed that the expression level of TGF-β was related to disease progression of asthma. In addition, fibroblasts isolated from clinical specimens of asthmatics express amounts of extracellular matrixs upon stimulated with TGF-β. And also, the studies in animal models indicated the possible important roles of TGF-β in asthma pathophysiology, through targeting TGF-β signaling with a variety of approaches, including exogenous administration, overexpression by transgene, gene knockout, blocking with monoclonal antibody or soluble recepter. However, the actual TGF-β effects reported by the studies are controversial, probably due to the application of different animal models, intervention approaches and detection techniques for TGF-β level. And thus, the roles of TGF-β especially in airway remodeling in severe chronic asthma, as well as the potentials of targeting TGF-β for the treatment purpose, remain to be unclear.This current study sought to investigate the possible roles of TGF-β in asthma pathogenesis, through using a new intervention strategy of active immunization to induce a persistent TGF-β-specific antibody response and assessing its effects on allergen-induced chronic airway inflammation, goblet cell hyperplasia, subepithelial fibrosis, and airway hyperresponsiveness. And also, the study aimed to evaluate the potentials of exploring TGF-β as a new therapeutic target and developing a vaccine for the clinical treatment of asthma.Firstly, TGF-P antigenic epitopes were chosen by bioinformatic analyses, and cloned into immunodominant region of hepatitis B core andtigen (HBcAg) by gene recombiannt techniques. The chimeric protein was expressed efficiently in E.coli cells, and presented in the form of virus-like particles (VLPs). Secondly, HBcAg/TGF-β VLPs were effectively purified and then used for mouse immunization. ELISA and Western-blot analyses indicated that HBcAg/TGF-P VLPs broke through immune tolerance and induced anti-TGF-β antibodies even without the use of conventional adjuvnts. The effects of different vaccine doses and applied adjuvants on antibody titer and duration were investigated. Thirdly, to clarify the intervention potentials of immuniztion with HBcAg/TGF-β VLPs, the derived ani-serum was used to successfully neutralize TGF-β activity in vitro, and significantly suppressed dimethynitrosamine - induced rat liver fibrosis in vivo through preventive immunization. Fourthly, in an acute asthma model induced with ovalbumin (OVA), preventive immunization with HBcAg/TGF-β VLPs effectively reduced the level of pSmad2/3 which are important molecules of TGF-β signaling, suppressed TGF-β activity in bronchoalveolar lavage fluids (BALF), elevated BALF level of Th2 inflammatory cytokines, and promoted serum OVA-IgE production; in addition, vaccination reduced siganificantly the accumulation of inflammatory cells in BALF, however it didn’t significantly influence OVA-induced lung tissue inflamamtion and airway goblet cell hyperplasia. Finally, in a chronic asthma model, VLPs immunization was therapeutically conducted when the airway inflammatory responses has been established. The results showed that, VLPs immunization promoted the production of OVA specific IgG2a, IgGi and IgE, enhanced the accumultion of imflammatory cytokines in BALF and the expression of Thl-type cytokine IFN-y and Th2-type cytokine IL-5 by incubated splenocytes, and significantly exerbated suatained inflammatory cells infiltration in lung tissue, airway goblet cell hyperplasia and airway hyperresponsiveness. In the other hand, vaccination significantly reduced subepithelial collagen deposition and suppressed gene expression of a-SMA and collagen I (al), indicating that OVA-induced fibrosis and smooth muscle hypertrophy were effectively ameliorated.The results demonstrated that active immunization with a vaccine successfully intervened TGF-P signaling, and ameliorated airway subepitelial collagen deposition, however excerbated persistent airway inflammation, mucus overproduction, and airway hyperresosiveness. The results strongly indicated that the role of TGF-β1 is complicated in allergic airway inflammatory responses, which may depond on specific immuopathologic mircoenvironment. It is important to make a careful assessment in accordance with specific disease conditions when targeting TGF-β1 for a therapeutic purpose. The current study adds our knowledge of the complexity and the possible role of TGF-β in asthma pathogenesis, and also provided useful information for evaluating the potentials of targeting TGF-β in the clinical treatment of asthma. |
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