With intensive study on airway inflammation mechanism of bronchial asthma, it has been found in recent years that a large number of neutrophils exist in bronchial biopsy and induced sputum of some patients with severe asthma and acute exacerbation of asthma, but there is no typical eosinophil infiltration[15~17].Neutrophils are the last differentiated cells with the shortest life span in blood cells and the most important inflammatory cells in body. Normally, neutrophils start their spontaneous apoptotic process from the beginning of maturation.Active damage and repair mechanisms may exist in the respiratory tract during the onset of asthma, and many mediators produced by neutrophils play an important role in this process.Studies have shown that the levels of IL-6, IL-8 and IL-17 in peripheral blood or BALF are significantly increased during acute attack of asthma, and these cytokines can inhibit the apoptosis of neutrophils and promote their aggregation into inflammatory airways[18~20].ICOSL molecule is the main member of CD28/B7 superfamily [8]. Because of its importance in T lymphocyte activation, polarization of Th1/Th2 subgroup and immunoglobulin homology transformation, ICOSL molecule has attracted much attention and become a research hotspot in immunology.In order to observe the pathophysiological effects of ICOSL in mice with neutrophilic asthma, the model of neutrophilic asthma was established by OVA + LPS, and ICOSL antibody was added to the model during induction period. Through the study of behavioral manifestations, characteristic cytokine levels of Th1, Th2 and Th17 cells and pathological changes of lung tissue to understand the role of ICOSL antibody intervention in neutrophilic asthma, and to deduce the pathophysiological role of ICOSL in neutrophilic asthma.In this experiment, the mice with neutrophilic asthma showed obvious sneezing, accelerated breathing, restlessness and frequent scratching of the face and neck skin. Lung histopathology showed obvious infiltration of neutrophils in lung tissue, alveolar interstitium and around the official cavity, hypersecretion of mucus in the official cavity, tracheal stenosis and so on, which indicated that the model of neutrophilic asthma in mice was successfully established.
During seven stimulations,asthma performance in group N was the earliest and obvious and was improved in group I,there was no asthma behavior in group C.In group N, the performance of asthma appeared earliest.The behavioral changes of mice after ICOSL intervention were delayed.,The overall clinical manifestations of group I were milder than those of group N.These results suggest that ICOSL antibody intervention before stimulation in mice with neutrophilic asthma can slow down the behavioral manifestation of asthma and alleviate the symptoms of asthma until the mice are tolerant to stimulation. It is inferred that ICOSL is involved in the occurrence, development and acute attack of neutrophilic asthma.
Current studies on ICOSL are mostly focused on inflammatory diseases, autoimmune diseases and tumors. ICOSL is highly expressed in inflammatory diseases and is closely related to the severity of inflammation[21].The role of ICOSL in asthma is relatively rare, and the conclusions are inconsistent.In Matsic's study, ICOS + T cells transfected with OVA-specific T cell receptor were transplanted into OVA-sensitized BALB/c mice,observed that lymphocytes, macrophages, neutrophils and eosinophils were significantly increased in bronchial lavage fluid[22].However, Akbari used allergen-induced asthma model in mice to study the role of ICOS/ICOSL signaling pathway. It was found that the co-stimulation of ICOS induced the production of regulatory T (Treg) cells. Treg cells depended on the high level of ICOSL expressed by pulmonary dendritic cells. Treg cells could inhibit the function of antigen-specific T cells and the formation of AHR[23~24].Lung histopathology showed that there were obvious infiltration of inflammatory cells and neutrophils and hypersecretion of airway mucus in group N and group G. After intervention with ICOSL antibody, the infiltration of inflammatory cells and mucus secretion in airway could be alleviated, indicating that ICOSL was involved in the pathological damage process of respiratory tract in neutrophilic asthma.Compared with group C, the percentage of total cells and neutrophils in BALF in group N was significantly higher than that in group C. The levels of cytokines IL-6, IL-13 and IL-17 in peripheral blood and BALF in group N were significantly higher than those in group C, and IFN-γwas decreased.The levels of IL-6, IL-13 and IL-17 decreased and IFN-γincreased after ICOSL antibody intervention compared with group N, but there were still differences compared with group C, suggesting that ICOSL antibody could partially alleviate the pathological and immune inflammation process of neutrophilic asthma.ICOSL antibodies were given to mice at 0, 3, 7, 10 and 14, respectively. The irritation time of mice was delayed compared with that of neutrophilic asthma group. No obvious nodding breathing was observed after continuous atomization for one week. The overall symptoms were improved, the infiltration of inflammatory cells in lung tissue and airway was alleviated, and the secretion of IL-6, IL-13 and IL-17 was also reduced. The aggregation of neutrophils in lung tissue was relatively reduced.All of these prove that ICOSL is a positive regulator, which can synergistically stimulate T cell proliferation and promote the secretion of various cytokines and chemokines.