| Summary: | 博士 === 國立成功大學 === 基礎醫學研究所 === 102 === Objective: Allergic asthma is a chronic disease characterized with allergen-induced airway inflammation, airway hyperreactivity (AHR), reversible airway obstruction, and airway remodeling. Previous researches have indicated that the immunopathogenesis of allergic asthma is due to predominant differentiation and activation of interleukin (IL)-4-, IL-5-, and IL-13-producing T helper (Th) 2 cells, which result in immunoglobulin (Ig)E- and eosinophil-mediated airway inflammation and AHR. However, recent studies also show that Th17 cells result in neutrophil-mediated airway inflammation and AHR. IL-6, a pleiotropic inflammatory cytokine secreted by antigen-stimulated dendritic cells (DCs), is essential for development of Th2 and Th17 cells, but its roles in allergic asthma and in DC differentiation and function remain unclear. Therefore, the first part of this study is to explore the role of IL-6 in animal models of allergic asthma and the influence of IL-6 on Th differentiation and function of CD4+CD25+ regulatory T (Treg) cells. In the second part, we hypothesize that IL-6 affects DC differentiation and function and their ability to induce airway inflammation and AHR. The third part of this study is to investigate the effect of blockade of IL-6 signaling on DC differentiation and function in allergic asthmatics.
Methods: In the first part of this study, we used two sensitization protocols of mouse models of allergic asthma to examine the role of IL-6 in Dermatophagoides pteronyssinus (Der p)-induced airway inflammation and AHR. In the intranasal model, wild-type (WT) and IL-6 knockout (KO) mice were intranasally instilled of Der p daily for 10 days. In the intraperitoneal model, WT and IL-6 KO mice were intraperitoneally sensitized with Der p emulsified in aluminum hydroxide and intratracheally challenged with Der p. We analyzed airway resistance, cell influx and cytokine production in bronchoalveolar lavage fluid (BALF), Ig production, Th differentiation, and suppressive function of CD4+CD25+ Treg cells of Der p-sensitized and -challenged WT and IL-6 KO mice. Part II: We detected percentages and function of CD11c+ DCs generated from bone marrow (BM) of WT and IL-6 KO mice. Der p-loaded CD11c+ bone marrow-derived DCs (BMDCs) from WT and IL-6 KO mice were adoptively transferred into naïve WT mice via intratracheal route, respectively. Then, recipient mice were intranasally challenged with Der p to induce airway inflammation and AHR. Part III: Peripheral blood monocytes, collected from non-atopic controls and Der p-sensitive, allergic asthmatics, were differentiated into DCs by incubation with recombinant human (rh) GM-CSF and rhIL-4. During this differentiation phase, monocytes were also treated in the absence (medium-DCs) and presence of tocilizumab (tocilizumab-DCs). Upon Der p stimulation, CD1a, CD11c, human histocompatibility leukocyte antigen (HLA)-DR, and CD86 expression, and ability to induce Th2 differentiation were compared between medium-DCs and tocilizumab-DCs.
Results: In Part I, as compared to Der p-sensitized and -challenged WT mice, AHR, recruited lymphocytes, eosinophils, neutrophils, and levels of tumor necrosis factor (TNF)-, IL-4, IL-17, CCL17, and CCL11 significantly decreased in the airway of Der p-sensitized and -challenged IL-6 KO mice in the intranasal and intraperitoneal models. Levels of Der p-specific IgG1, IL-4, IL-5, IL-13, and IL-17 also markedly reduced in Der p-sensitized and -challenged IL-6 KO mice. However, as compared to Der p-sensitized and -challenged WT mice, significantly increased Foxp3 expression on CD4+CD25+ Treg cells was observed in Der p-sensitized and -challenged IL-6 KO mice. Moreover, lung CD4+CD25+ Treg cells of Der p-sensitized and -challenged IL-6 KO mice also had better capability in inhibiting CD4+CD25- T cell proliferation than that of Der p-exposed WT mice. Part II: We found that there was higher frequency of CD11c+ DCs generated from WT BM than that from IL-6 KO BM. Further exploration of BMDCs from IL-6 KO mice revealed that they had weaker activity of phagocytosis and lower MHC class II and CD86 expression in response to LPS, TNF-a, and Der p stimulation than those of WT BMDCs. Der p-loaded CD11c+ BMDCs from IL-6 KO mice failed to induce Th2 and Th17 differentiation. Moreover, adoptive transfer of Der p-loaded BMDCs from IL-6 KO mice also showed a functional defect in their inability to trigger airway inflammation and AHR in recipient mice. Part III: Tocilizumab had no influence on CD1a and CD11c expression on monocyte-derived DCs in non-atopic controls and allergic asthmatics. Upon Der p stimulation, HLA-DR and CD86 expression on tocilizumab-DCs were significantly lower than those on medium-DCs in allergic asthmatics. Moreover, tocilizumab-DCs had poor capacity for eliciting Th2 polarization as compared to medium-DCs in allergic asthmatics.
Conclusion: IL-6 plays a central role in the pathogenesis of allergic asthma. IL-6 can induce Th2 and Th17 differentiation and inhibit function of CD4+CD25+ Treg cells to trigger and amplify airway inflammation and AHR. IL-6 signaling in DCs is essential for their uptake of allergens, maturation, activation of naïve CD4+ T cells, and initiation of Th2 and Th17-mediated airway inflammation and AHR in allergic asthma, thus providing a new potential target for treating patients with allergic asthma.
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