受損細胞所釋放出之內源性危險訊號引發肥大細胞活化

Abstract

細胞壞死後會釋出許多原本存在於細胞內的物質，統稱為 damage-associated molecular patterns (DAMPs)，這些物質會引起體內的急性發炎反應，而這種類型的發炎反應稱為無菌發炎反應，其目的為移除細胞殘骸，避免造成周圍組織持續性的傷害，以及恢復組織內恆定；但是過多的白血球聚集到發炎反應部位卻反而對周圍正常細胞組織造成傷害，並引起許多相關疾病產生。目前對於無菌發炎反應的機制尚未完全了解透徹，然而可以確定的是，組織中具有能夠偵測到壞死細胞所釋放之 DAMPs 的感測細胞，才能引發無菌發炎反應的發生；而肥大細胞為一種廣泛存在於組織中的免疫細胞，當其受到刺激而活化時，會釋放出一些蛋白酶及發炎介質來引起發炎反應的發生。因此本研究中我們將探討肥大細胞在無菌發炎反應中所扮演之角色，實驗結果顯示，壞死細胞所釋放出的 DAMPs 不僅可刺激小鼠骨髓肥大細胞進行去顆粒化作用及分泌促發炎反應激素，也可刺激人類肥大細胞株 LUVA 進行去顆粒化作用，確認了肥大細胞確實可受到壞死細胞的活化，具有作為無菌發炎反應中感測細胞的能力；然而，先前研究中所指出 DAMPs 中能夠刺激肥大細胞分泌促發炎細胞激素之 IL-33，在本研究中發現其並不具有刺激肥大細胞進行去顆粒化作用的能力。此外透過酵素處理壞死細胞上清的實驗，我們發現 DAMPs 中的 DNA 與 RNA 類的物質皆可刺激肥大細胞分泌促發炎細胞激素，而只有 DNA 具有刺激肥大細胞進行去顆粒化作用的能力。本研究也模擬了在過敏反應下，同時有細胞壞死情形發生的狀態，實驗發現壞死細胞與 IgE 共同刺激肥大細胞時，對於刺激肥大細胞之活化具有加成性的效果。由本研究結果顯示，肥大細胞在細胞壞死所引起的無菌發炎反應中佔有重要地位，因此如果能對於肥大細胞的功能進行調節，也許將來可以應用於治療相關發炎疾病。

Cells dying by necrosis release intracellular components, so-called damage-associated molecular patterns (DAMPs), which induce an acute sterile inflammatory response. The physiological function of the sterile inflammatory response is to clear cell debris and restore tissue homeostasis. However, leukocytes recruited to the inflamed site may also cause damage to healthy tissue, which is thought to contribute to the pathogenesis of many diseases. The underlying mechanisms for how cell death triggers inflammation have yet to be elucidated. To induce inflammatory response, the DAMPs released from dying cells need to be recognized by cellular sensors in the local tissue environment. Mast cells normally reside in tissues, and upon activation, these cells release proteolytic enzymes and proinflammatory mediators, resulting in an inflammatory response. In this study, we investigated the role of mast cell as a cellular sensor for cell injury. We found that DAMPs released from necrotic cells could stimulate the degranulation and cytokine production of murine bone marrow-derived mast cells, and also degranulation of human LUVA mast cells. These indicate that mast cells may function as a cellular sensor for cell injury. IL-33 was shown previously to be a DAMP and stimulate mast cells to produce proinflammatory cytokines; however, IL-33 did not stimulate the degranulation of mast cells. Other unidentified DAMP(s) (e.g., DNA) may be responsible for stimulating mast cell degranulation. We also found that necrotic cell stimulation and IgE receptor ligation have synergistic effects in activating cytokine production and the degranulation of BMMCs. Our results indicate that mast cells play a key role in regulating the inflammatory responses to cell death and therapeutic strategies targeting mast cells could be considering for treating diseases associated with sterile inflammation.