口服 Dp2 重組蛋白質對致敏小鼠過敏免疫調節之影響

Abstract

台灣氣喘病患中有八成對塵蟎過敏，其中最主要的過敏原之一即是 Dermatophagoides pteronyssinus 2 (Dp2)。氣喘疾病之特徵為呼吸道慢性發炎、發炎性細胞聚集，導致氣管阻塞、肺呼吸阻力增加。利用口服給予過敏原以降低過敏原專一性之免疫反應，稱為“口服耐受性” (oral tolerance)。本研究以轉型酵母菌 (Pichia pastoris)生產 Dp2 重組蛋白 (recombinant Dp2, rDp2)，使用此蛋白致敏 BALB/c 小鼠及氣管內刺激建立氣喘模式，並進一步探討給予致敏小鼠口服不同劑量 Dp2，對呼吸道發炎反應、T細胞調節及腸道免疫反應之影響。實驗 (一) 以七週大之雌鼠連續管餵 7 天 rDp2，餵食劑量分別為 0 μg/day (Control 組)、100 μg/day (O1 組)、200 μg/day (O2組)、500 μg/day (O5組)。實驗 (二) 則加入更高劑量之 1000 μg/day (O10 組)和 2000 μg/day (O20 組)。口服實驗第 1、5、14、21 天以腹腔注射 rDp2 進行致敏，空白組為注射 PBS。致敏結束後一週採集血樣以分析 Dp2 特異性抗體。第28、30天進行氣管內注射 Dp2 誘發小鼠氣喘症狀後，進行呼吸阻力測定。犧牲時收取小鼠肺沖洗液、脾臟細胞、皮耶氏節 (Peyer’s patch) 淋巴細胞及小腸後段均質液，分別進行肺沖洗液細胞組成計數、初代細胞培養與腸道 IgA 抗體分析。結果顯示，餵食 500 μg 以上之劑量除了可顯著減緩致敏小鼠肺呼吸阻力，並且降低發炎性細胞聚集，肺沖洗液中有顯著下降之 IL-4、較高的 IL-10 分泌量。同時血清中 Dp2 特異性 IgE 和總 IgE 量顯著較餵食 buffer 之 Control 組低。小腸的總 IgA 含量於各組之間無顯著差異，但 O5組具有顯著較低之腸道 Dp2 特異性 IgA。在脾臟及皮耶氏節細胞激素分泌方面，餵食劑量 500 μg 以上皆有顯著較低之 IL-4 分泌，於 Th1 傾向之細胞激素：IL-2 和 IFN-γ 則無顯著差異。口服各劑量 rDp2 對非特異性刺激下脾臟增生無顯著影響，但在抗原 rDp2 刺激下，各組皆具有較低之脾臟增生能力。實驗 (三) 則以 500 μg rDp2 餵食七天後即進行犧牲，觀察在餵食過敏原短期內，是否即影響到全身性免疫系統，結果顯示：口服過敏原七天後即可顯著抑制脾臟細胞特異性增生反應，並且同時有顯著較低的 IL-2 及 IL-5 分泌量。綜合以上結果，短期口服較高劑量之過敏原 rDp2能誘發口服耐受性，可能藉由抑制 Th2 免疫反應、減少 IL-4 生成進而調節 B 細胞的同型轉換(class switch) 使 IgE 減少，並減緩過敏性呼吸道發炎之現象。

Sensitization to house dust mite (HDM) is an important risk factor for the development of allergic asthma. Among any other allergens isolated from HDM, the prevalence of hypersensitivity to Dermatophagoides pteronyssinus group 2 protein (Dp2) is the highest. Oral tolerance is defined as a state of immunological unresponsiveness to a specific antigen after exposure to that antigen by enteric route. One of the main goals of the present study is to evaluate the effects of feeding the major allergen Dp2 on allergic airway inflammation and gastroenteric immunity. In order to generate pure Dp2 in quantities sufficient for oral feeding, transformed Pichia pastoris was used to produce recombinant Dp2 (rDp2). In experiment I and II, female BALB/c mice were tube fed daily with rDp2 (100, 200, 500, 1000, 2000 µg/day: O1, O2, O5, O10, O20 group, Control group was fed with 3% Na2CO3) from day 1-7, at the same time sensitized by intraperitoneal injection of rDp2 with aluminum hydroxide and pertussis toxin as ajuvant, then intra-tracheal challenged with rDp2 to establish airway inflammation. Oral administered 500 μg rDp2 or higher doses resulted in significant lowered airway hypersensitivity, reduced inflammative cells infiltration, IL-4 secretion in BALF, and elevated IL-10 level in BALF. While group O2, O5, O10, O20 showed decreased titers of serum Dp2-specific IgE, total IgE, and IL-4 secreted by splenocytes and Peyer’s patch, feeding 500 μg rDp2 could also significantly reduce enteric Dp2-specific IgA compared with buffer-fed (Control) group. Also, the allergen-specific splenocyte proliferation was inhibited by oral administered rDp2. In experiment III, BALB/c mice was fed 500 μg rDp2 for 7 days, then sacrificed on day 8 in order to evaluate whether short-term allergen feeding already change the systemic immune system. We found that the inhibitory effect was established right after the oral treatment of allergen, splenocyte specific proliferation was significantly reduced, IL-5 and IL-2 secretions were also inhibited. In conclusion, short-term oral administration of higher-dose Dp2 induced oral tolerance, inhibited both local and systemic Th2 response, and significantly relieved airway allergic hypersensitivity.