The unconventional T cell compartment encompasses a variety of cell subsets that straddle the line between innate and adaptive immunity, often reside at mucosal surfaces and can recognize a wide range of non-polymorphic ligands. Recent advances have highlighted the role of unconventional T cells in tissue homeostasis and disease. In this Review, we recast unconventional T cell subsets according to the class of ligand that they recognize; their expression of semi-invariant or diverse T cell receptors; the structural features that underlie ligand recognition; their acquisition of effector functions in the thymus or periphery; and their distinct functional properties. Unconventional T cells follow specific selection rules and are poised to recognize self or evolutionarily conserved microbial antigens. We discuss these features from an evolutionary perspective to provide insights into the development and function of unconventional T cells. Finally, we elaborate on the functional redundancy of unconventional T cells and their relationship to subsets of innate and adaptive lymphoid cells, and propose that the unconventional T cell compartment has a critical role in our survival by expanding and complementing the role of the conventional T cell compartment in protective immunity, tissue healing and barrier function.

非常规的 T 细胞区室包含多种细胞亚群，它们跨越先天免疫和适应性免疫之间的界限，通常位于粘膜表面，并且可以识别广泛的非多态性配体。最近的进展突出了非常规 T 细胞在组织稳态和疾病中的作用。在这篇综述中，我们根据非常规 T 细胞亚群识别的配体类别对其进行了改造；它们表达半不变或多样化的 T 细胞受体；配体识别的结构特征；他们在胸腺或外周获得效应功能；以及它们独特的功能特性。非常规 T 细胞遵循特定的选择规则，并准备识别自身或进化上保守的微生物抗原。我们从进化的角度讨论这些特征，以提供对非常规 T 细胞发育和功能的见解。最后，我们详细阐述了非常规 T 细胞的功能冗余及其与先天和适应性淋巴细胞亚群的关系，并提出非常规 T 细胞区室通过扩展和补充常规 T 细胞的作用，在我们的生存中发挥关键作用保护性免疫、组织愈合和屏障功能。