title: Phagocyte-induced antigen-specific activation of unprimed CD8+ T cells in vitro.
abstract: The strict segregation of the major histocompatibility complex (MHC) class I and class II loading pathways has been challenged by recent reports indicating that MHC class I molecules can acquire antigen in the phagocytic pathway. We now show that this alternative peptide loading pathway can be used efficiently to generate macrophages able to activate unprimed antigen-specific cytotoxic T cells in vitro. Short peptides (8-11 residues), administered in the phagocytic pathway at nanomolar concentrations, were found to be effective in specifically activating naïve cytotoxic T lymphocytes (CTL) in vitro, but longer peptides or whole protein antigen were not. Whole protein antigen coated on beads did, however, render macrophages susceptible to lysis by an antigen-specific CTL clone. This indicates that proteolysis in the phagocytic pathway has limited capability for class I-restricted presentation. We propose a model for class I loading in the phagocytic pathway consisting of direct trafficking of nascent MHC class I from the trans-Golgi network to the phagosome, prior to appearance at the cell surface, and the use of the narrow cavity between bead and phagosomal membrane as a peptide exchange/loading compartment. Targeting immunogenic class I-binding peptide to the phagocytic pathway of macrophages facilitates presentation in association with class I. This is a useful tool for CTL response induction in vitro.
authors.affiliation: Department of Immunology, Scripps Research Institute, La Jolla, USA.
authors.forename: M L
authors.initials: ML
authors.lastname: De Bruijn
authors.forename: M R
authors.initials: MR
authors.lastname: Jackson
authors.forename: P A
authors.initials: PA
authors.lastname: Peterson
mesh_terms: D000327:Adsorption; D000595:Amino Acid Sequence; D000818:Animals; D017951:Antigen Presentation; D002460:Cell Line; D000939:Epitopes / Q000008:administration & dosage / Q000276:immunology*; D006183:H-2 Antigens / Q000276:immunology*; D007840:Latex; D008213:Lymphocyte Activation; D008247:Lysosomes / Q000276:immunology; D017737:Macrophages, Peritoneal / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008863:Microspheres; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000008:administration & dosage / Q000276:immunology*; D010587:Phagocytosis; D011489:Protein Denaturation; D013047:Specific Pathogen-Free Organisms; D013154:Spleen / Q000166:cytology; D016176:T-Lymphocyte Subsets / Q000276:immunology; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*
chemical_list: D000939:Epitopes; D006183:H-2 Antigens; C032876:H-2Kb protein, mouse; D007840:Latex; D010446:Peptide Fragments