The monomorphic MHC-class I-like molecule, MR1, presents small metabolites to T cells. MR1 is the restriction element for microbe-reactive mucosal-associated invariant T (MAIT) cells. MAIT cells have limited TCR usage, including a semi-invariant TCR alpha chain and express high levels of CD161 and CD26. In addition to microbial lumazine metabolites, recent studies have demonstrated that MR1 is able to capture a variety of diverse chemical entities including folate-derivatives, a number of drug-like and other synthetic small molecules, and as yet undefined compounds of self-origin. This capacity of MR1 to bind distinct ligands likely accounts for the recent identification of additional, non-canonical, subsets of MR1-restricted T (MR1T) cells. These subsets can be defined based on their ability to recognize diverse microbes as well as their reactivity to non-microbial cell-endogenous ligands, including tumor-associated antigens. Herein, we will discuss our current understanding of MR1T cell diversity in terms of TCR usage, ligand recognition and functional attributes.

单态 MHC I 类分子 MR1 向 T 细胞呈递小代谢物。MR1 是微生物反应性黏膜相关不变 T (MAIT) 细胞的限制元件。MAIT 细胞的 TCR 使用有限，包括半不变的 TCR α 链并表达高水平的 CD161 和 CD26。除了微生物 lumazine 代谢物外，最近的研究表明，MR1 能够捕获多种不同的化学实体，包括叶酸衍生物、许多药物样和其他合成小分子，以及尚未确定的自身来源化合物。MR1 结合不同配体的这种能力可能解释了最近发现的额外的、非规范的 MR1 限制性 T (MR1T) 细胞亚群。这些亚群可以根据它们识别不同微生物的能力以及它们对非微生物细胞内源性配体（包括肿瘤相关抗原）的反应性来定义。在这里，我们将从 TCR 使用、配体识别和功能属性方面讨论我们目前对 MR1T 细胞多样性的理解。