困難梭狀桿菌是一個產孢子的絕對厭氧革蘭氏陽性菌， 臨床上常造成抗生素相關腹瀉及偽膜性腸炎並成為全球院內感染的主要致病菌之一。表面層蛋白Surface layer proteins (SLPs) 為困難梭狀桿菌菌體最外層蛋白中表達量最豐富的。表面層蛋白的刺激已知可以活化宿主的TLR4 介導先天及後天免疫反應，但實際上表面層蛋白在困難梭狀桿菌感染中所扮演的角色仍未被清楚地探討。在我們先前的研究中發現ATP-P2X7 介導的發炎體（Inflammasome）活化及細胞焦亡（Pyroptosis）為困難梭狀桿菌感染重要的現象及機制。而在本研究中更近一步的證實在不同核糖體型（Ribotye）的困難梭狀桿菌及其表面層蛋白都有能力透過宿主細胞膜表面富含膽固醇的脂筏Lipid raft引起發炎體的活化。脂筏被廣泛地認為在宿主細胞的訊息傳遞與細菌的黏附中扮演重要角色。根據前述研究發現透過甲基環糊精（MβCD）移除細胞膜表面膽固醇能降低困難梭狀桿菌及其表面層蛋白所引發的發炎體活化程度。我們更近一步將兩種已被美國食藥署核准的膽固醇干擾藥物HPβCD 和Pitavastatin應用於困難梭狀桿菌的感染模型中，並在實驗中發現此兩種藥物都能有效減少困難梭狀桿菌及其表面層蛋白所誘發的發炎體活化。而在小鼠感染模型中也能看到上述兩種藥物能有效改善原本感染造成的體重下降、盲腸減輕、糞便組成及腸道病理特徵。這些現象都指向減少或阻斷脂筏介導的訊息傳遞能夠減輕發炎反應帶來的症狀及影響。總結，在本篇我們發現表面層蛋白誘導的脂筏聚集和訊息傳遞在困難梭狀桿菌感染及其誘發的發炎體活化中扮演關鍵角色。

Clostridioides difficile is an obligate anaerobic gram-positive pathogen that frequently leads to antibiotic-associated diarrhea and is one of the leading causes of nosocomial infection worldwide. Surface layer proteins (SLPs) are the most abundant surface localized proteins expressed by C. difficile. Treatment of SLPs has been shown to activate innate and adaptive immunity mediated by TLR4 signaling in the host cells. However, the role of SLPs in C. difficile infection has not yet been fully elucidated. Our previous study indicated that the ATP-P2X7 mediated inflammasome activation and pyroptosis play critical roles in host defense during C. difficile infection (CDI). Here, we found that infection by whole bacterium or derived SLPs from different C. difficile ribotypes both induced inflammasome activation through cholesterol-rich microdomains on the cell membrane (also referred to as lipid rafts). Lipid rafts are considered to be crucial for bacterial adhesion and signal transduction. Based on our previous findings, the inflammasome activations induced by SLPs or C. difficile were abrogated by MβCD (methyl-β-cyclodextrin), a membrane cholesterol removing agent. We further evalute the other two FDA-approved cholesterol-disrupting agents HPβCD (hydroxypropyl-β-cyclodextrin) and pitavastatin for therapeutic capacity of CDI. Treatments of both agents were able to lower the inflammasome activation against the challenge of SLPs or C. difficile. In CDI experimental murine model, mice treated with either HPβCD or pitavastatin exhibited an improvement in CDI-induced loss of body weight and cecum weight, and alteration of stool consistency and colon pathology. These findings illustrated that blocking the lipid raft mediated signaling alleviated symptoms through eliminating inflammatory effects. Collectively, the SLPs-induced lipid rafts mediated signaling may be a key step for C. difficile colonization and inducing inflammasome activation.

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