Pathogens are ubiquitous and a constant threat to their hosts, which has led to the evolution of sophisticated immune systems in bacteria, archaea and eukaryotes. Bacterial immune systems encode an astoundingly large array of antiviral (antiphage) systems, and recent investigations have identified unexpected similarities between the immune systems of bacteria and animals. In this Review, we discuss advances in our understanding of the bacterial innate immune system and highlight the components, strategies and pathogen restriction mechanisms conserved between bacteria and eukaryotes. We summarize evidence for the hypothesis that components of the human immune system originated in bacteria, where they first evolved to defend against phages. Further, we discuss shared mechanisms that pathogens use to overcome host immune pathways and unexpected similarities between bacterial immune systems and interbacterial antagonism. Understanding the shared evolutionary path of immune components across domains of life and the successful strategies that organisms have arrived at to restrict their pathogens will enable future development of therapeutics that activate the human immune system for the precise treatment of disease.

病原体无处不在，并对其宿主持续构成威胁，这导致细菌、古细菌和真核生物中复杂的免疫系统的进化。细菌免疫系统编码数量惊人的抗病毒（抗噬菌体）系统，最近的研究发现细菌和动物的免疫系统之间存在意想不到的相似之处。在这篇综述中，我们讨论了对细菌先天免疫系统的理解进展，并重点介绍了细菌和真核生物之间保守的组成部分、策略和病原体限制机制。我们总结了这一假设的证据，即人类免疫系统的组成部分起源于细菌，它们首先在细菌中进化以防御噬菌体。此外，我们讨论了病原体用来克服宿主免疫途径的共同机制，以及细菌免疫系统和细菌间拮抗作用之间意想不到的相似性。了解生命各领域免疫成分的共同进化路径以及生物体限制病原体的成功策略，将使未来开发出激活人类免疫系统以精确治疗疾病的疗法。