title: Endosomal MR1 Trafficking Plays a Key Role in Presentation of Mycobacterium tuberculosis Ligands to MAIT Cells.
abstract: Mucosal-Associated Invariant T (MAIT) cells, present in high frequency in airway and other mucosal tissues, have Th1 effector capacity positioning them to play a critical role in the early immune response to intracellular pathogens, including Mycobacterium tuberculosis (Mtb). MR1 is a highly conserved Class I-like molecule that presents vitamin B metabolites to MAIT cells. The mechanisms for loading these ubiquitous small molecules are likely to be tightly regulated to prevent inappropriate MAIT cell activation. To define the intracellular localization of MR1, we analyzed the distribution of an MR1-GFP fusion protein in antigen presenting cells. We found that MR1 localized to endosomes and was translocated to the cell surface upon addition of 6-formyl pterin (6-FP). To understand the mechanisms by which MR1 antigens are presented, we used a lentiviral shRNA screen to identify trafficking molecules that are required for the presentation of Mtb antigen to HLA-diverse T cells. We identified Stx18, VAMP4, and Rab6 as trafficking molecules regulating MR1-dependent MAIT cell recognition of Mtb-infected cells. Stx18 but not VAMP4 or Rab6 knockdown also resulted in decreased 6-FP-dependent surface translocation of MR1 suggesting distinct pathways for loading of exogenous ligands and intracellular mycobacterially-derived ligands. We postulate that endosome-mediated trafficking of MR1 allows for selective sampling of the intracellular environment.
authors.affiliation: Portland VA Medical Center, Portland, Oregon, United States of America.|Pulmonary & Critical Care Medicine, Oregon Health & Science University, Portland, Oregon, United States of America.
authors.forename: Melanie J
authors.initials: MJ
authors.lastname: Harriff
authors.affiliation: Portland VA Medical Center, Portland, Oregon, United States of America.|Pulmonary & Critical Care Medicine, Oregon Health & Science University, Portland, Oregon, United States of America.
authors.forename: Elham
authors.initials: E
authors.lastname: Karamooz
authors.affiliation: Portland VA Medical Center, Portland, Oregon, United States of America.
authors.forename: Ansen
authors.initials: A
authors.lastname: Burr
authors.affiliation: Pulmonary & Critical Care Medicine, Oregon Health & Science University, Portland, Oregon, United States of America.
authors.forename: Wilmon F
authors.initials: WF
authors.lastname: Grant
authors.affiliation: Pulmonary & Critical Care Medicine, Oregon Health & Science University, Portland, Oregon, United States of America.
authors.forename: Elizabeth T
authors.initials: ET
authors.lastname: Canfield
authors.affiliation: Portland VA Medical Center, Portland, Oregon, United States of America.
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Sorensen
authors.affiliation: Instituto Gulbenkian de Ciência, Oeiras, Portugal.
authors.forename: Luis F
authors.initials: LF
authors.lastname: Moita
authors.affiliation: Portland VA Medical Center, Portland, Oregon, United States of America.|Pulmonary & Critical Care Medicine, Oregon Health & Science University, Portland, Oregon, United States of America.|Molecular Microbiology and Immunology, Oregon Health & Science University, Portland, Oregon, United States of America.
authors.forename: David M
authors.initials: DM
authors.lastname: Lewinsohn
mesh_terms: D017951:Antigen Presentation / Q000276:immunology*; D011992:Endosomes / Q000378:metabolism*; D015395:Histocompatibility Antigens Class I / Q000276:immunology / Q000378:metabolism*; D006801:Humans; D008213:Lymphocyte Activation / Q000276:immunology*; D015778:Minor Histocompatibility Antigens; D009092:Mucous Membrane / Q000378:metabolism; D009169:Mycobacterium tuberculosis / Q000276:immunology*; D021381:Protein Transport / Q000502:physiology*; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000235:genetics; D016176:T-Lymphocyte Subsets / Q000276:immunology
chemical_list: D015395:Histocompatibility Antigens Class I; C094840:MR1 protein, human; D015778:Minor Histocompatibility Antigens; D016693:Receptors, Antigen, T-Cell, alpha-beta