During microbial infection, pre-existing memory CD8⁺ T cells that are not specific for the infecting pathogens can be activated by cytokines without cognate antigens, termed bystander activation. Studies in mouse models and human patients demonstrate bystander activation of memory CD8⁺ T cells, which exerts either protective or detrimental effects on the host, depending on the infection model or disease. Research has elucidated mechanisms underlying the bystander activation of CD8⁺ T cells in terms of the responsible cytokines and the effector mechanisms of bystander-activated CD8⁺ T cells. In this Review, we describe the history of research on bystander CD8⁺ T cell activation as well as evidence of bystander activation. We also discuss the mechanisms and immunopathological roles of bystander activation in various microbial infections.

在微生物感染期间，对感染病原体不具有特异性的预先存在的记忆 CD8 ⁺ T 细胞可以被没有同源抗原的细胞因子激活，称为旁观者激活。对小鼠模型和人类患者的研究表明，旁观者激活了记忆 CD8 ⁺ T 细胞，这取决于感染模型或疾病，对宿主产生保护或有害作用。研究已经从负责的细胞因子和旁观者激活的 CD8 ⁺ T 细胞的效应机制方面阐明了 CD8 ⁺ T 细胞的旁观者激活的机制。^{在这篇评论中，我们描述了旁观者 CD8 +}的研究历史T 细胞激活以及旁观者激活的证据。我们还讨论了旁观者激活在各种微生物感染中的机制和免疫病理学作用。