Department of Immunology, University of Pittsburgh, Pittsburgh, PA 15260, USA.
Toxins (Basel). 2013 Jun 6;5(6):1105-18. doi: 10.3390/toxins5061105.
Pore-forming toxins are utilized by bacterial and mammalian cells to exert pathogenic effects and induce cell lysis. In addition to rapid plasma membrane repair, macrophages respond to pore-forming toxins through activation of the NLRP3 inflammasome, leading to IL-1β secretion and pyroptosis. The structural determinants of pore-forming toxins required for NLRP3 activation remain unknown. Here, we demonstrate using streptolysin O (SLO) that pore-formation controls IL-1β secretion and direct toxicity. An SLO mutant incapable of pore-formation did not promote direct killing, pyroptosis or IL-1β production. This indicated that pore formation is necessary for inflammasome activation. However, a partially active mutant (SLO N402C) that was less toxic to macrophages than wild-type SLO, even at concentrations that directly lysed an equivalent number of red blood cells, enhanced IL-1β production but did not alter pyroptosis. This suggests that direct lysis may attenuate immune responses by preventing macrophages from successfully repairing their plasma membrane and elaborating more robust cytokine production. We suggest that mutagenesis of pore-forming toxins represents a strategy to enhance adjuvant activity.
成孔毒素被细菌和哺乳动物细胞用于发挥致病作用并诱导细胞裂解。除了快速的质膜修复外，巨噬细胞还通过 Nlrp3 炎性小体的激活对成孔毒素作出反应，导致 Il-1β 的分泌和细胞焦亡。Nlrp3 激活所需的成孔毒素的结构决定因素尚不清楚。在这里，我们使用链球菌溶血素 O（SLO）证明，孔形成控制 Il-1β 的分泌和直接毒性。不能形成孔的 SLO 突变体不能促进直接杀伤、细胞焦亡或 Il-1β 的产生。这表明孔形成对于炎性小体的激活是必要的。然而，一种部分活性的突变体（SLO N402C）比野生型 SLO 对巨噬细胞的毒性更小，即使在浓度足以直接溶解相当数量的红细胞时，也能增强 Il-1β 的产生，但不改变细胞焦亡。这表明直接溶解可能通过阻止巨噬细胞成功修复质膜并产生更强烈的细胞因子来减弱免疫反应。我们认为，成孔毒素的突变代表了一种增强佐剂活性的策略。
