Mucosal‐associated invariant T (MAIT) cells are an abundant subset of innate‐like T lymphocytes. MAIT cells are activated by microbial riboflavin‐derived antigens, such as 5‐(2‐oxopropylideneamino)‐6‐d‐ribitylaminouracil (5‐OP‐RU), when presented by the major histocompatibility complex (MHC) class I‐related protein (MR1). We have synthesized all stereoisomers of 5‐OP‐RU to investigate the effects of its stereochemistry on the MR1‐dependent MAIT cell activation and MR1 upregulation. The analysis of MAIT cell activation by these 5‐OP‐RU isomers revealed that the stereocenters at the 2’‐ and 3’‐OH groups in the ribityl tail are crucial for the recognition of MAIT‐TCR, whereas that of 4’‐OH group does not significantly affect the regulation of MAIT cell activity. Furthermore, kinetic analysis of complex formation between the ligands and MR1 suggested that 5‐OP‐RU forms a covalent bond to MR1 in cells within 1 hour. These findings provide guidelines for designing ligands that regulate MAIT cell functions.

A total synthesis of polyoxamic acid has been achieved. The key feature of the synthetic route is a visible-lightmediated β-scission and carbon-to-carbon 1,5-hydrogen atom transfer (1,5-HAT) to provide the functionalized alditol under mild conditions. This type of carbon-to-carbon 1,5-HAT initiated by C(sp 3 )-centered radicals has been scarcely reported. Furthermore, the reaction was adapted for flow chemistry, facilitating the total synthesis of polyoxamic acid.

Mucosal-associated invariant T (MAIT) cells are innate-like T cells that are modulated by ligands presented on MHC class I-related proteins (MR1). These cells have attracted attention as potential drug targets because of their involvement in the initial response to infection and various disorders. Herein, we have established the MR1-presentation reporter assay system employing split-luciferase, which enables the efficient exploration of MR1 ligands. Using our screening system, we identified herbal medicine-derived MR1 ligands, including coniferyl aldehyde, which have an ability to inhibit the MR1–MAIT cell axis. Coniferyl aldehyde comprises phenylpropanoids and is a novel motif for MR1 ligands. Further structure-activity relationship study revealed the key structural features of ligands required for MR1 recognition. These results will contribute to uncovering the mode of action of herbal medicines and their analogs, and to developing novel MAIT cell modulators.

Recently, various metabolites derived from host microbes have been reported to modulate the immune system, with potential involvement in health or diseases. Archaea, prokaryotic organisms, are present in the human body, but their connection with the host is largely unknown when compared with other microorganisms such as bacteria. This study focused on unique glycerolipids from symbiotic methanogenic archaea and evaluated their activities toward an innate immune receptor. The results revealed that archaeal lipids were recognized by the C-type lectin receptor Mincle and induced immune responses. A concurrent structure-activity relationship study identified key structural features of archaeal lipids required for recognition by Mincle. Subsequent gene expression profiling suggested qualitative differences between the symbiotic archaeal lipid and the pathogenic bacteria-derived lipid. These findings have broad implications for understanding the function and pathogenicity of symbiotic archaea to host health and diseases.

Recently, various metabolites derived from host microbes have been reported to modulate the immune system, with potential involvement in health or diseases. Archaea, prokaryotic organisms, are present in the human body, but their connection with the host is largely unknown when compared to other microorganisms such as bacteria. This study focused on unique glycerolipids from symbiotic methanogenic archaea and evaluated their activities toward an innate immune receptor. The results revealed that archaeal lipids were recognized by the C-type lectin receptor Mincle and induced immune responses. A concurrent structure−activity relationship study identified the key structural features of archaeal lipids required for recognition by Mincle. Subsequent gene expression profiling suggested qualitative differences between the symbiotic archaeal lipid and the pathogenic bacteria-derived lipid. These findings have broad implications for understanding the function of symbiotic archaea in host health and diseases.