利用基因轉殖小鼠的氣喘模式研究口服耐受性之機制

Abstract

利用口服給與抗原的方式，可以誘導針對此種特定抗原的免疫耐受性(immune tolerance)現象產生，而這種現象或許將會是一個用來治療諸如氣喘等免疫疾病的一種方式。近年來的研究也指出，藉由持續口服給與小鼠卵白蛋白(ovalbumin, OVA)這種抗原，可以誘導小鼠產生口服耐受性(oral tolerance)的現象，而這種現象，目前推測是因為活化調節性T細胞(regulatory T cells)；或是因為抗原專一性T細胞(antigen-specific T cells)的減少(deletion)。不過引起口服耐受性的詳細機制目前仍不清楚；因此，本次研究中，我們利用帶有OVA-T細胞受器(OVA-T cell receptor)基因的基因轉殖小鼠，做為研究的實驗動物。透過此種動物氣喘模式的建立，同時給與基因轉殖小鼠口服餵食不同劑量的卵白蛋白，誘導針對卵白蛋白抗原之口服耐受性的產生，並觀察產生口服耐受性之小鼠與氣喘小鼠在呼吸道過度反應(airway hyperresponsiveness)上的差異性，以及肺部沖洗液中，浸潤到肺部細胞型態的分佈情況，並藉此檢視抗原專一性T細胞的變化。本次實驗中，我們發現給予餵食卵白蛋白而產生口服耐受性的小鼠，其呼吸道過度反應測試比起利用抗原致敏的老鼠還要降低許多，而肺沖洗液中的嗜伊紅性白血球(eoxinophil)的數量也減低許多，進一步的檢測小鼠細胞激素的分泌則發現，被誘導產生口服耐受的小鼠，其體內Th2細胞激素IL-4，比起氣喘致敏的小鼠有著明顯減少，但對於過敏免疫反應有調節性的細胞激素包括IL-10和TGF-

Oral administration of antigens can induce immune tolerance to specific antigens and this characteristic phenomenon might be used as a potential treatment for allergic diseases, such as asthma. Recent researches have shown that oral tolerance induced by continuous feeding of ovalbumin (OVA) in the murine model can result in the activation of regulatory T cells and/or deletion of antigen-specific T cells. However, the underlying mechanisms are yet to be clarified. Therefore, we would like to study further the functional change of antigen-specific T cells after oral tolerance induction. We use OVA-T-cell receptor (OVA-TCR) transgenic mice on the BALB/c background, which recognizes the 323-339 peptide fragment of OVA, as model animal. First, we established an animal model with airway hyperresponsiveness, antigen specific IgE production and eosinophilia in OVA-TCR transgenic mice. In this study, oral tolerance was induced by feeding different dose of OVA, and then examined the number and function of OVA-specific T cells. The results showed that oral tolerance induced by both high-dose and low-dose of OVA could suppress the reactivity of asthma, such as the reduction of Th2-cytokine (IL-4, IL-5) secretion, decreased airway hyperresponsiveness, reduced eosinophila, and increase regulatory cytokine (TGF-β and IL-10) secretion. Furthermore, the numbers of OVA-specific T cell were increased in the group with high-dose oral tolerance. Taken together, these findings indicate that oral tolerance induced by feeding low-dose of antigen generates TGF-β-secreting T cells, and that high-dose oral tolerance can be achieved by angeric antigen-specific T cells. Although much more studies are needed, these results suggest that TGF-β may play a crucial role in the induction of oral tolerance.