探討invariant NKT細胞的活化對於過敏性呼吸道發炎反應之影響

The Effect of Activation of Invariant NKT Cells on the Allergic Airway Inflammation

王姿君(Tzu-Chun Wang)

指導教授 ： 莊雅惠

國立臺灣大學/醫學院/醫學檢驗暨生物技術學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.01985

摘要

氣喘是一肺部發炎疾病，其臨床表徵為鳴喘、呼吸急促與呼吸道過度反應，許多免疫細胞都會參與發炎的過程，例如：T helper 2（Th2）cells和eosinophils。natural killer T cells（NKT cells）是一群特殊的T cells，它會表現natural killer cells和conventional T cells兩者的特性，目前在invariant natural killer cells（iNKT cells）的研究最多。當iNKT cells辨識由CD1d所呈獻的抗原如α-galactosylceramide（α-GalCer）而活化後，可在數小時內快速分泌多種且大量的細胞激素如interferon-γ（IFN-γ）和interleukin-4（IL-4），這獨特的特性使iNKT cell在許多疾病中扮演調控的角色。有關NKT cells在氣喘中扮演之角色先前研究的結果並不一致，有團隊證明NKT cells會促進氣喘的產生，但另有團隊卻證明NKT cells的活化會抑制呼吸道過度反應與呼吸道發炎反應。此外， NKT cells在某些疾病不同進程時扮演不同的角色。本研究的目的是探討是否NKT cells在氣喘不同疾病進程中亦扮演不同的角色，我們在氣喘疾病進程中不同時期以α-GalCer活化iNKT cells後測量小鼠呼吸道發炎之嚴重程度是否會不同以及其機轉。
我們利用ovalbumin（OVA）致敏引發氣喘的小鼠模式，在OVA致敏前或OVA致敏後給予α-GalCer，之後分析小鼠呼吸道發炎反應的程度。實驗結果顯示OVA致敏前給予α-GalCer的小鼠其呼吸道發炎反應高於致敏後才給予α-GalCer的小鼠，證實在氣喘疾病不同時期給予α-GalCer活化iNKT cells確實會使小鼠產生不同嚴重程度之呼吸道發炎反應。接著我們分析致敏前或致敏後給予α-GalCer兩小時與五天後小鼠的免疫反應之變化，發現在OVA致敏前給予α-GalCer可活化iNKT cells分泌大量的Th2 cytokines例如IL-4、IL-5與IL-13，及使肺部TSLP與eotaxin濃度升高，導致肺部浸潤細胞增多及IL-4的顯著上升。但若是在OVA致敏後才給予α-GalCer則造成Th2 cytokines與thymic stromal lymphopoietin （TSLP）的降低，終使小鼠呼吸道發炎反應不如OVA致敏前給予α-GalCer之小鼠嚴重。
這些結果顯示naïve環境下的iNKT cells與氣喘病Th2為主的環境下的iNKT cells其活化後產生的反應不同，最後造成呼吸道發炎反應之嚴重度不同。然而欲將α-GalCer當作呼吸道佐劑或治療性藥物的時候，需注意eosinophilia的可能性。

關鍵字

氣喘 ； NKT細胞 ； 呼吸道發炎反應 ； α-galactosylceramide (α-GalCer) ； 支氣管肺泡沖洗液

並列摘要

Asthma is an inflammatory lung disease characterized by the expansion of T helper 2 (Th2) cells and eosinophils as well as the production of allergen-specific IgE. Natural killer T (NKT) cell is a unique subset of T cells that coexpresses T cell receptor (TCR) and natural killer (NK) cell markers. The most studied NKT cells are Type 1 NKT cells, which also referred to invariant natural killer T cell (iNKT cells). iNKT cells express semi-invariant CD1d-restricted αβ TCR, therefore they can recognize glycolipid antigens (like α-galactosylceramide (α-GalCer)) presented by CD1d molecules on antigen presenting cells. Once NKT cells are activated, they rapidly produce large amount of cytokines, such as interferon-γ (IFN-γ) and interleukin-4 (IL-4). Due to this unique characteristic, they have been implicated in the regulation of immune responses associated with a broad range of diseases.
In allergic asthma, the roles of iNKT cells are controversial. Some studies demonstrate that NKT cells are important in the development of asthma. However, others demonstrate that NKT cell activation before challenge abolishes the airway hyperresponsiveness and airway inflammation in experimental murine asthma models. These studies imply that NKT cells may play different roles in different asthma progression. Furthermore, this theory has been proved in some autoimmune diseases and allergic conjunctivitis. The aim of this study is to investigate the effect of activation of iNKT cells on the allergic airway inflammation and its mechanism.
We administered BALB/c mice with α-GalCer, a stimulator for NKT cell activation, before or after ovalbumin (OVA) immunization and measured airway inflammation of those mice after 2 times of intranasal OVA challenge. In our results, the airway inflammation was more serious in mice that administered with α-GalCer before OVA immunization than that of after OVA immunization, suggesting that activation of iNKT cells in different asthma progression could lead to different severity of airway inflammation. Moreover, we analyzed the cell components and cytokines expression in lung after 2 hours and 5 days of α-GalCer administration to study the mechanism. Our data demonstrated that mice administered with α-GalCer before OVA immuniztion could activate iNKT cells to secrete large amount of Th2 cytokines, such as IL-4, IL-5 and IL-13, and increase eotaxin and thymic stromal lymphopoietin (TSLP) expression in bronchoalveolar lavage fluid (BALF), which recruit cell infiltrate in lung. In contrast, administration of α-GalCer after OVA immunization decreased Th2 cytokines, TSLP, and airway inflammation when compared to mice administered with a-GalCer before OVA immunization.
Our data demonstrated that different immune response was noted in activation of naïve NKT cells and Th2-dominant environment NKT cells, which led to different outcome of airway inflammation in mice. However, the potential risks of treatment with NKT cell activation in human diseases should be considered.

並列關鍵字

asthma ； natural killer T cell (NKT cell) ； airway inflammation ； α-galactosylceramide (α-GalCer) ； bronchoalveolar lavage fluid (BALF)

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