細顆粒引發之急性呼吸道發炎及嗜中性球增多之免疫機制探討

Abstract

細顆粒物(fine particular matter, FPM)係指空氣懸浮微粒中，直徑小於2.5微米(μm)的顆粒。先前研究已指出細顆粒物與急性、慢性肺部發炎有關，但詳細的致病原因並未明確。因此，本篇研究目的為進一步探討細顆粒物引發肺炎的機制。我們的實驗結果發現嗜中性球(neutrophil)及自然殺手T細胞(invariant nature killer T cell, iNKT)細胞都參與細顆粒物引發肺炎反應。在小鼠的疾病模式中，我們經由鼻腔給予小鼠細顆粒物。並藉由連續三天、每天一次的鼻腔注射引發小鼠的急性肺炎。我們的數據指出，經過三天的鼻腔注射，以嗜中性球為主的白血球會浸潤至肺部氣道腔室(airway lumen)中、介白素17A (interleukin-17A, IL-17A)會被製造以及釋放。在缺乏iNKT細胞的Jα18-/-小鼠中，鼻腔注射細顆粒物引發了更嚴重的嗜中性球浸潤以及更大量的介白素17A。另外，根據細胞內染及流式細胞儀的實驗結果，我們認為在我們所觀察的時間點上，嗜中性球為主要製造介白素17A的細胞。為了更進一步探討嗜中性球以及介白素17A兩者之間可能存在的關係，我們對小鼠施打抗體以阻斷介白素17A的作用，或者消除小鼠體內的嗜中性球。在抗體的作用下，嗜中性球的減少的確降低了介白素17A；阻斷介白素17A之後，我們發現嗜中性球以及嗜中性球趨化素CXCL1、CXCL2皆有顯著的下降。另外，病理上的特徵，包括黏液相關的基因muc5ac、gob5之表達、表皮細胞的不正常增厚，在介白素17A受到抗體的阻斷後亦有顯著的緩解。總而言之，嗜中性球以及介白素17A之間存在著一種正回饋迴圈，且兩者皆為促進肺炎之重要因子。其中iNKT細胞如何影響此迴圈以及疾病的嚴重程度也是我們將回答的問題之一。對此，我們的初步的結果顯示，在鼻腔注射細顆粒物的小鼠中，iNKT細胞提高了FasL的表現量，且嗜中性球在細顆粒物的刺激前後持續表現大量的Fas以及CD1d。因此，我們推測iNKT細胞是藉由FasL與Fas的交互作用引發嗜中性球的死亡，並藉此減緩肺炎的嚴重程度。

Fine particulate matter (FPM) denotes the small particle size fraction (2.5μm in diameter) of ambient suspended particles. It has been shown the exposure of FPM is related to both the acute and chronic lung inflammation. However, the etiology of FPM-induced lung inflammation remains unclear. Thus, we would like to investigate the pathogenesis of FPM-induced lung inflammation. In this study, we investigated a previously unrevealed mechanism of FPM-induced acute airway inflammation, which involved neutrophils and iNKT cells. Our data showed that acute inflammation in mice was induced by FPM given intranasally once per day for three days. After FPM exposure, we found neutrophils were the major cell population infiltrating into airway lumen. Furthermore, we noticed IL-17A was also induced by FPM. Both neutrophil infiltration and IL-17A production became more severe in iNKT cell-deficient Jα18-/- mice. We also demonstrated that neutrophil was the major producer of IL-17A after FPM exposure. In addition, the depletion of neutrophils attenuated the secretion of IL-17A and severity of inflammation in the lung. Furthermore, the blockade of IL-17A attenuated the secretions of neutrophil-recruiting chemokines, CXCL1 and CXCL2, Muc5ac, Gob5, as well as neutrophilia in the lung. Moreover, the upregulation of FasL expression on iNKT cells after FPM exposure was observed. Since lung neutrophil constitutively expression of Fas and CD1d, suggesting that iNKT cells may limit both IL-17A and neutrophil number by inducing neutrophil apoptosis through Fas-FasL interaction. Taken together, FPM exposure induced neutrophil infiltration and IL-17A production, in turns resulting in lung inflammation and epithelial hypertrophy. This acute inflammation could be restricted by iNKT cell through triggering neutrophil apoptosis via the Fas-FasL interaction.