Wang Qiang, Imamura Ryu, Motani Kou, Kushiyama Hiroko, Nagata Shigekazu, Suda Takashi
Division of Immunology and Molecular Biology, Cancer Research Institute, Kanazawa University, Kanazawa, Ishikawa 920-1192, Japan.
Int Immunol. 2013 Jun;25(6):363-72. doi: 10.1093/intimm/dxs161. Epub 2013 Feb 26.
Pathogenic intracellular bacteria often hijack macrophages for their propagation. The infected macrophages release IL-1β and IL-18 and simultaneously commit suicide, which is called pyroptosis; both responses require caspase-1. Here, we found that pyroptotic cells induced by microbial infection were efficiently engulfed by human monocytic THP-1-cell-derived macrophages or mouse peritoneal macrophages. This engulfment was inhibited by the D89E mutant of milk fat globule (MFG) epidermal growth factor (EGF) factor 8 (MFG-E8; a phosphatidylserine-binding protein) that has been shown previously to inhibit phosphatidylserine-dependent engulfment of apoptotic cells by macrophages, suggesting that the engulfment of pyroptotic cells by macrophages was also phosphatidylserine dependent. Using a pair of cell lines that respectively exhibited pyroptosis or apoptosis after muramyl dipeptide treatment, we showed that both pyroptotic and apoptotic cells bound to a T-cell immunoglobulin and mucin domain-containing 4 (Tim4; another phosphatidylserine-binding protein)-coated plate, whereas heat-killed necrotic cells did not, indicating that phosphatidylserine was externalized in pyroptosis and apoptosis but not in accidental necrosis. Macrophages engulfed apoptotic cells most efficiently, followed by pyroptotic and then heat-killed necrotic cells. Pyroptotic cells also released a macrophage attractant(s), 'find-me' signal, whose activity was diminished by apyrase that degrades nucleoside triphosphate to nucleoside monophosphate. Heat-killed necrotic cells and pyroptotic cells released ATP much more efficiently than apoptotic cells. These results suggest that pyroptotic cells, like apoptotic cells, actively induce phagocytosis by macrophages using 'eat-me' and find-me signals. Based on these results, a possible role of coordinated induction of pyroptosis and inflammatory cytokine production is discussed.
致病性胞内细菌常常劫持巨噬细胞以进行繁殖。被感染的巨噬细胞会释放白细胞介素-1β（IL-1β）和白细胞介素-18（IL-18），同时发生自杀，这被称为细胞焦亡；这两种反应都需要半胱天冬酶-1（caspase-1）。在此，我们发现由微生物感染诱导的细胞焦亡细胞能被人单核细胞系THP-1细胞来源的巨噬细胞或小鼠腹腔巨噬细胞有效吞噬。这种吞噬作用被乳脂肪球（MFG）表皮生长因子（EGF）8（MFG-E8；一种磷脂酰丝氨酸结合蛋白）的D89E突变体所抑制，该突变体先前已被证明可抑制巨噬细胞对凋亡细胞的磷脂酰丝氨酸依赖性吞噬，这表明巨噬细胞对细胞焦亡细胞的吞噬也是磷脂酰丝氨酸依赖性的。使用一对在胞壁酰二肽处理后分别表现出细胞焦亡或凋亡的细胞系，我们发现细胞焦亡和凋亡细胞都能结合到包被有含T细胞免疫球蛋白和粘蛋白结构域4（Tim4；另一种磷脂酰丝氨酸结合蛋白）的平板上，而热杀死的坏死细胞则不能，这表明磷脂酰丝氨酸在细胞焦亡和凋亡过程中会外化，但在意外坏死中不会。巨噬细胞最有效地吞噬凋亡细胞，其次是细胞焦亡细胞，然后是热杀死的坏死细胞。细胞焦亡细胞还会释放一种巨噬细胞吸引剂，即“找到我”信号，其活性会被将三磷酸核苷降解为单磷酸核苷的腺苷三磷酸双磷酸酶所减弱。热杀死的坏死细胞和细胞焦亡细胞比凋亡细胞更有效地释放三磷酸腺苷（ATP）。这些结果表明，细胞焦亡细胞与凋亡细胞一样，利用“吃掉我”和“找到我”信号积极诱导巨噬细胞的吞噬作用。基于这些结果，我们讨论了细胞焦亡和炎性细胞因子产生的协同诱导的可能作用。
