title: Negative regulation of T-cell activation and autoimmunity by Mgat5 N-glycosylation.
abstract: T-cell activation requires clustering of a threshold number of T-cell receptors (TCRs) at the site of antigen presentation, a number that is reduced by CD28 co-receptor recruitment of signalling proteins to TCRs. Here we demonstrate that a deficiency in beta1,6 N-acetylglucosaminyltransferase V (Mgat5), an enzyme in the N-glycosylation pathway, lowers T-cell activation thresholds by directly enhancing TCR clustering. Mgat5-deficient mice showed kidney autoimmune disease, enhanced delayed-type hypersensitivity, and increased susceptibility to experimental autoimmune encephalomyelitis. Recruitment of TCRs to agonist-coated beads, TCR signalling, actin microfilament re-organization, and agonist-induced proliferation were all enhanced in Mgat5-/- T cells. Mgat5 initiates GlcNAc beta1,6 branching on N-glycans, thereby increasing N-acetyllactosamine, the ligand for galectins, which are proteins known to modulate T-cell proliferation and apoptosis. Indeed, galectin-3 was associated with the TCR complex at the cell surface, an interaction dependent on Mgat5. Pre-treatment of wild-type T cells with lactose to compete for galectin binding produced a phenocopy of Mgat5-/- TCR clustering. These data indicate that a galectin-glycoprotein lattice strengthened by Mgat5-modified glycans restricts TCR recruitment to the site of antigen presentation. Dysregulation of Mgat5 in humans may increase susceptibility to autoimmune diseases, such as multiple sclerosis.
authors.affiliation: Samuel Lunenfeld Research Institute, Mount Sinai Hospital, Toronto, Ontario, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Demetriou
authors.forename: M
authors.initials: M
authors.lastname: Granovsky
authors.forename: S
authors.initials: S
authors.lastname: Quaggin
authors.forename: J W
authors.initials: JW
authors.lastname: Dennis
mesh_terms: D000818:Animals; D000943:Antigens, Differentiation / Q000378:metabolism; D015551:Autoimmunity; D037502:Galectin 3; D006031:Glycosylation; D006801:Humans; D006968:Hypersensitivity, Delayed; D008213:Lymphocyte Activation; D008285:Major Histocompatibility Complex; D051379:Mice; D017351:N-Acetylglucosaminyltransferases / Q000172:deficiency / Q000378:metabolism*; D011134:Polysaccharides / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000276:immunology*
chemical_list: D000943:Antigens, Differentiation; D037502:Galectin 3; D011134:Polysaccharides; D011948:Receptors, Antigen, T-Cell; D017351:N-Acetylglucosaminyltransferases; C052254:alpha-1,6-mannosylglycoprotein beta 1,6-N-acetylglucosaminyltransferase