This episode features Dr. McWilliam, who discusses the intricate microbial immune-detection system in mammals revolving around MR1, a highly conserved protein. MR1 plays a crucial role in capturing vitamin B-related metabolite antigens from various microbes and displaying them at the cell surface to stimulate MR1-restricted lymphocytes, including mucosal-associated invariant T (MAIT) cells.

This process of MR1 presentation and MAIT cell recognition aids in maintaining homeostasis through host defense and tissue repair mechanisms. However, the cellular mechanisms that regulate MR1 cell surface expression, which are critical for its function and MAIT cell recognition, remain largely unexplored.

Dr. McWilliam and his team report that human MR1 is equipped with a tyrosine-based motif in its cytoplasmic domain that facilitates low-affinity binding with the endocytic adaptor protein 2 (AP2) complex. This interaction regulates the rate of MR1 internalization from the cell surface and restricts recycling.

They propose that MR1 utilizes AP2 endocytosis to determine the duration of antigen presentation to MAIT cells and the detection of a microbial metabolic signature by the immune system. Join us in this episode to delve deeper into the exciting world of MR1 and MAIT cells with Dr. McWilliam.

Key Words: MR1, Microbial Immune-Detection, Mucosal-Associated Invariant T Cells, Endocytic Adaptor Protein 2, Antigen Presentation, Host Defense.

McWilliam et al. A specialized tyrosine-based endocytosis signal in MR1 controls antigen presentation to MAIT cells. doi: 10.1083/jcb.202110125. Epub 2022 Sep 21. PMID: 36129434; PMCID: PMC9499830.