間葉幹細胞應用在改善氣喘動物模式呼吸道發炎的機制探討

Abstract

氣喘是兒童常見的過敏性疾病之一，在過去幾年來其發生率有逐年增加的趨勢。目前已知過敏性氣喘是由第二型T輔助細胞所引起，通常伴隨有呼吸道過度反應和嗜酸性白血球浸潤，黏液分泌過多，甚至是呼吸道重塑等症狀。間葉幹細胞 (mesenchymal stem cells, MSCs) 來自於骨髓中，屬於多潛能性幹細胞 (multipotent stem cells)，是一種具有自我更新、繁殖並能分化成不同種類的組織和任一型態的細胞。近年來，有許多研究報告顯示間葉幹細胞具有免疫調節的功能。本篇研究希望透過小鼠尾巴靜脈注射方式打入間葉幹細胞，藉此降低由卵清蛋白 (ovalbumin, OVA)所誘發的發炎現象。首先，我們利用老鼠骨髓細胞培養出間葉幹細胞，並在適當的刺激下，體外培養分化成骨細胞 (osteocytes)和脂肪細胞 (adipocytes)，同時確認間葉幹細胞的表面標誌。此外，我們在試管內測試間葉幹細胞其免疫抑制的功能，發現在免疫細胞刺激劑 (Concanavalin A, ConA）刺激下，或是在混和淋巴細胞反應 (mixed lymphocyte reaction, MLR)中，當脾臟淋巴細胞與間葉幹細胞共同培養時，間葉幹細胞都能有效抑制脾臟淋巴細胞的增生。更進一步地，我們利用OVA致敏BALB/c小鼠，並以尾巴靜脈注射方式打入間葉幹細胞，再給予鼻腔刺激OVA引發呼吸道發炎，藉以研究其治療效果。結果顯示，給予間葉幹細胞可有效緩和呼吸道過度反應，減輕肺部沖洗液中嗜酸性白血球的發炎反應，以及降低血清中OVA特異性的IgE含量。此外，在給予間葉幹細胞的小鼠其脾臟淋巴細胞經OVA刺激下，不僅能抑制脾臟淋巴細胞的增生，同時可產生大量的介白素-10 (interleukin-10, IL-10)和干擾素-γ (interferon-γ, IFN-γ)。因此，我們認為給予間葉幹細胞能減緩過敏性氣喘的傾向，未來將會更進一步研究間葉幹細胞在免疫抑制上的作用機制。

Asthma is one of the most common allergic diseases in children and its prevalence has been increased in recent decades. Allergic asthma is characterized by the induction of T helper 2 cells, airway hyperresponsiveness, eosinophil infiltration, increased mucus secretion and even airway remodeling. Mesenchymal stem cells (MSCs) are a self-renewing population of multipotent stem cells present in bone marrow and can differentiate into a variety of tissues or cell lineages. Recent studies have demonstrated that MSCs could exert an immunosuppressive function. This study was performed to investigate whether MSCs could inhibit OVA-induced allergic airway inflammation in murine model. First, MSCs were isolated from mouse bone marrow, characterized by their phenotypes, and differentiated into osteocytes and adipocytes in the appropriate induction media. In addition, the immunosuppressive function of MSCs was determined in vitro. The results indicated that MSCs exerted effectively inhibitory effect on the proliferation of lymphocytes under ConA stimulation or the mixed lymphocyte reaction. Furthermore, to investigate the effect of MSCs on the allergic asthma, the female BALB/c mice were sensitized with ovalbumin (OVA) by intraperitoneal injection, 1×106 MSCs were injected intravenously before each OVA challenge. In the study, we found that the airway hyperresponsiveness, eosinophilic inflammation in bronchoalveolar lavage fluid, and OVA-sprcific IgE in serum were diminished after MSCs administration. Additionally, MSCs delivered in mice not only inhibited the proliferation of OVA-specific lymphocytes but also increased the levels of IL-10 and IFN-γ. Therefore, we demonstrated that administration of MSCs could alleviate airway inflammation in OVA-induced murine model of asthma. In the future, it will be interesting to clarify the immunomodulatory mechanisms of MSCs.