title: Evidence for MR1 antigen presentation to mucosal-associated invariant T cells.
abstract: The novel class Ib molecule MR1 is highly conserved in mammals, particularly in its alpha1/alpha2 domains. Recent studies demonstrated that MR1 expression is required for development and expansion of a small population of T cells expressing an invariant T cell receptor (TCR) alpha chain called mucosal-associated invariant T (MAIT) cells. Despite these intriguing properties it has been difficult to determine whether MR1 expression and MAIT cell recognition is ligand-dependent. To address these outstanding questions, monoclonal antibodies were produced in MR1 knock-out mice immunized with recombinant MR1 protein, and a series of MR1 mutations were generated at sites previously shown to disrupt the ability of class Ia molecules to bind peptide or TCR. Here we show that 1) MR1 molecules are detected by monoclonal antibodies in either an open or folded conformation that correlates precisely with peptide-induced conformational changes in class Ia molecules, 2) only the folded MR1 conformer activated 2/2 MAIT hybridoma cells tested, 3) the pattern of MAIT cell activation by the MR1 mutants implies the MR1/TCR orientation is strikingly similar to published major histocompatibility complex/alphabetaTCR engagements, 4) all the MR1 mutations tested and found to severely reduce surface expression of folded molecules were located in the putative ligand binding groove, and 5) certain groove mutants of MR1 that are highly expressed on the cell surface disrupt MAIT cell activation. These combined data strongly support the conclusion that MR1 has an antigen presentation function.
authors.affiliation: Department of Pathology and Immunology, Washington University, St. Louis, Missouri 63110, USA.
authors.forename: Shouxiong
authors.initials: S
authors.lastname: Huang
authors.forename: Susan
authors.initials: S
authors.lastname: Gilfillan
authors.forename: Marina
authors.initials: M
authors.lastname: Cella
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Miley
authors.forename: Olivier
authors.initials: O
authors.lastname: Lantz
authors.forename: Lonnie
authors.initials: L
authors.lastname: Lybarger
authors.forename: Daved H
authors.initials: DH
authors.lastname: Fremont
authors.forename: Ted H
authors.initials: TH
authors.lastname: Hansen
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000737:chemistry; D017951:Antigen Presentation; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D003001:Cloning, Molecular; D004306:Dose-Response Relationship, Immunologic; D005434:Flow Cytometry; D015395:Histocompatibility Antigens Class I / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D006825:Hybridomas / Q000378:metabolism; D008024:Ligands; D051379:Mice; D018345:Mice, Knockout; D015778:Minor Histocompatibility Antigens; D008958:Models, Molecular; D009092:Mucous Membrane / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D011485:Protein Binding; D011487:Protein Conformation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship; D013601:T-Lymphocytes / Q000378:metabolism*; D014162:Transfection
chemical_list: D000911:Antibodies, Monoclonal; D015395:Histocompatibility Antigens Class I; D008024:Ligands; C094840:MR1 protein, human; D015778:Minor Histocompatibility Antigens