title: Sensitization of MHC class I-restricted T cells to exogenous proteins: evidence for an alternative class I-restricted antigen presentation pathway.
abstract: Immunization with exogenous proteins usually fails to immunize CD8+ T cells in vivo. Here we report that chicken ovalbumin (OVA) denatured by heat or sodium dodecyl sulphate (SDS) effectively induced CD8+ cytolytic T cells in vivo. The cytolytic T-lymphocyte (CTL) population generated recognized syngeneic target cells pulsed with the immunodominant OVA peptide (257-264) or transfected with the OVA protein-encoding gene. To analyse the mechanisms of how denatured OVA enters the class I-restricted pathway of antigen presentation, we took advantage of the fact that denatured OVA sensitizes target cells in vitro for lysis by OVA-specific CTL. We found that neither inhibition of protein synthesis (by cycloheximide) nor blocking of transport via the Golgi apparatus (by brefeldin A) interfered with the class I-restricted presentation of denatured OVA in vitro. In addition, transporter associated with antigen presentation (TAP)-dependent transport into the endoplasmic reticulum (ER) was not required for effective presentation, as TAP-deficient cells (RMA-S) could be sensitized effectively by denatured OVA for recognition by class I-restricted CTL. In contrast, class I-restricted presentation of denatured OVA was sensitive to lysosomotropic agents (NH4Cl, vinblastine and leupeptin), indicating that endosomal-like compartments are involved in the presentation of denatured OVA. Sensitization was inhibited at low temperature, yet took place in the presence of sucrose and in the absence of K+, indicating that denatured OVA enters the cell via fluid-phase endocytosis. Hence the results provide further evidence for an alternative class I-restricted pathway of antigen presentation for exogenous proteins. As that pathway seems to be effective in vivo, it offers a new and effective way of vaccination of CD8+ CTL.
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017951:Antigen Presentation / Q000276:immunology*; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D004705:Endocytosis / Q000276:immunology; D005260:Female; D015395:Histocompatibility Antigens Class I / Q000276:immunology*; D006358:Hot Temperature; D008247:Lysosomes / Q000276:immunology; D051379:Mice; D008810:Mice, Inbred C57BL; D008969:Molecular Sequence Data; D010047:Ovalbumin / Q000276:immunology*; D011489:Protein Denaturation; D012967:Sodium Dodecyl Sulfate
chemical_list: D015395:Histocompatibility Antigens Class I; D012967:Sodium Dodecyl Sulfate; D010047:Ovalbumin