title: Major histocompatibility complex (MHC) class II-peptide complexes arrive at the plasma membrane in cholesterol-rich microclusters.
abstract: BACKGROUND
  Antigen-specific CD4 T cells are activated by small numbers of antigenic peptide-MHC class II (pMHC-II) complexes on dendritic cells (DCs).
  
  
  RESULTS
  Newly generated pMHC-II complexes are present in small clusters on the DC surface.
  
  
  CONCLUSIONS
  pMHC-II clusters permit efficient T cell activation.
  
  
  CONCLUSIONS
  The appearance of clustered pMHC-II reveals the organization of the T cell antigen receptor ligand on the DC surface. Dendritic cells (DCs) function by stimulating naive antigen-specific CD4 T cells to proliferate and secrete a variety of immunomodulatory factors. The ability to activate naive T cells comes from the capacity of DCs to internalize, degrade, and express peptide fragments of antigenic proteins on their surface bound to MHC class II molecules (MHC-II). Although DCs express tens of thousands of distinct MHC-II, very small amounts of specific peptide-MHC-II complexes are required to interact with and activate T cells. We now show that stimulatory MHC-II I-A(k)-HEL(46-61) complexes that move from intracellular antigen-processing compartments to the plasma membrane are not randomly distributed on the DC surface. Confocal immunofluorescence microscopy and quantitative immunoelectron microscopy reveal that the majority of newly generated MHC-II I-A(k)-HEL(46-61) complexes are expressed in sub-100-nm microclusters on the DC membrane. These microclusters are stabilized in cholesterol-containing microdomains, and cholesterol depletion inhibits the stability of these clusters as well as the ability of the DCs to function as antigen-presenting cells. These results demonstrate that specific cohorts of peptide-MHC-II complexes expressed on the DC surface are present in cholesterol-dependent microclusters and that cluster integrity is important for antigen-specific naive CD4 T cell activation by DCs.
authors.affiliation: Experimental Immunology Branch, NCI, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Berta
authors.initials: B
authors.lastname: Bosch
authors.forename: Erica L
authors.initials: EL
authors.lastname: Heipertz
authors.forename: James R
authors.initials: JR
authors.lastname: Drake
authors.forename: Paul A
authors.initials: PA
authors.lastname: Roche
mesh_terms: D000818:Animals; D017951:Antigen Presentation; D000941:Antigens / Q000276:immunology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D002784:Cholesterol / Q000378:metabolism*; D003713:Dendritic Cells / Q000276:immunology / Q000378:metabolism; D000949:Histocompatibility Antigens Class II / Q000378:metabolism*; D008213:Lymphocyte Activation; D008563:Membrane Lipids / Q000378:metabolism; D021962:Membrane Microdomains / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D021381:Protein Transport
chemical_list: D000941:Antigens; D000949:Histocompatibility Antigens Class II; D008563:Membrane Lipids; D002784:Cholesterol
keywords: Dendritic Cells; Lipid Raft; Major Histocompatibility Complex (MHC); Membrane Trafficking; T Cell