The conventional perception asserts that immunology is the science of ‘discrimination’ between self and non-self. This concept is however no longer tenable as effector cells of the adaptive immune system are first conditioned to be tolerant to the body’s own antigens, collectively known as self until now. Only then attain these effectors the responsiveness to non-self. The acquisition of this essential state of tolerance to self occurs for T cells in the thymus, the last major organ of our body that revealed its intricate function in health and disease. The ‘thymus’ as an anatomical notion was first notably documented in Ancient Greece although our present understanding of the organ’s functions was only deciphered commencing in the 1960s. In the late 1980s, the thymus was identified as the site where clones of cells reactive to self, termed ‘forbidden’ thymocytes, are physically depleted as the result of a process now known as negative selection. The recognition of this mechanism further contributed to the belief that the central rationale of immunology as a science lies in the distinction between self and non-self. This review will discuss the evidence that the thymus serves as a unique lymphoid organ able to instruct T cells to recognize and be tolerant to harmless self before adopting the capacity to defend the body against potentially injurious non-self-antigens presented in the context of different challenges from infections to exposure to malignant cells. The emerging insight into the thymus’ cardinal functions now also provides an opportunity to exploit this knowledge to develop novel strategies that specifically prevent or even treat organ-specific autoimmune diseases.

传统观念认为，免疫学是自我与非自我之间“歧视”的科学。但是，由于适应性免疫系统的效应细胞首先要适应机体自身的抗原（迄今为止统称为自身），因此这一概念不再成立。只有这样，才能使这些效应器对非自我的反应。胸腺中的T细胞发生了这种自我耐受的基本状态，胸腺是我们身体的最后一个主要器官，在健康和疾病中显示出其复杂的功能。尽管我们目前对器官功能的了解只是从1960年代才开始破译，但“胸腺”作为解剖学概念最早在古希腊得到了证明。在1980年代后期，胸腺被确定为细胞克隆与自身，所谓的“禁止”胸腺细胞在物理上被消耗，这是现在称为阴性选择的过程的结果。对这一机制的认识进一步促进了人们的信念，即免疫学作为一门科学的中心原理在于自我与非自我之间的区别。这篇综述将讨论以下证据：胸腺是一种独特的淋巴器官，能够指导T细胞识别并耐受无害的自我，然后才有能力针对不同情况下出现的潜在伤害性非自身抗原防御身体从感染到暴露于恶性细胞的挑战。现在，对胸腺主要功能的新见解还提供了一个机会，可以利用这一知识来开发专门预防或什至治疗器官特异性自身免疫性疾病的新颖策略。