title: Distinct MHC class II molecules are associated on the dendritic cell surface in cholesterol-dependent membrane microdomains.
abstract: Very small amounts of MHC class II-peptide complexes expressed on the surface of antigen-presenting cells (APCs) are capable of stimulating antigen-specific CD4 T cells. There is intense interest to elucidate the molecular mechanisms by which these small amounts of MHC-II can cluster, cross-link T cell receptors, and promote T cell proliferation. We now demonstrate that a significant fraction of the total pool of MHC-II molecules on the surface of dendritic cells is physically associated in macromolecular aggregates. These MHC-II/MHC-II interactions have been probed by co-immunoprecipitation analysis of the MHC-II I-A molecule with the related I-E molecule. These molecular associations are maintained in gentle detergents but are disrupted in harsh detergents such as Triton X-100. MHC-II I-A/I-E interactions are disrupted when plasma membrane cholesterol is extracted using methyl β-cyclodextrin, suggesting that lipid raft microdomains are important mediators of these MHC-II interactions. Although it has been proposed that tetraspanin proteins regulate molecular clustering, aggregation, and co-immunoprecipitation in APCs, genetic deletion of the tetraspanin family members CD9 or CD81 had no effect on MHC-II I-A/I-E binding. These data demonstrate that the presence of distinct forms of MHC-II with plasma membrane lipid rafts is required for MHC-II aggregation in APCs and provides a molecular mechanism allowing dendritic cells expressing small amounts of MHC-II-peptide complexes to cross-link and stimulate CD4 T cells.
authors.affiliation: Experimental Immunology Branch, NCI, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: Sanjay
authors.initials: S
authors.lastname: Khandelwal
authors.forename: Paul A
authors.initials: PA
authors.lastname: Roche
mesh_terms: D000818:Animals; D000938:Antigen-Presenting Cells / Q000276:immunology / Q000378:metabolism; D015703:Antigens, CD / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology / Q000378:metabolism; D045744:Cell Line, Tumor; D002784:Cholesterol / Q000276:immunology* / Q000378:metabolism; D003713:Dendritic Cells / Q000276:immunology* / Q000378:metabolism; D005434:Flow Cytometry; D000949:Histocompatibility Antigens Class II / Q000276:immunology* / Q000378:metabolism; D015151:Immunoblotting; D047468:Immunoprecipitation; D008562:Membrane Glycoproteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D021962:Membrane Microdomains / Q000276:immunology* / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D011485:Protein Binding; D060225:Tetraspanin 28; D060245:Tetraspanin 29
chemical_list: D015703:Antigens, CD; C554799:Cd81 protein, mouse; C554870:Cd9 protein, mouse; D000949:Histocompatibility Antigens Class II; C024138:I-E-antigen; D008562:Membrane Glycoproteins; D060225:Tetraspanin 28; D060245:Tetraspanin 29; D002784:Cholesterol