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Original Article |
Correspondence to: Ronald N. Germain, Lymphocyte Biology Section, National Institutes of Health, National Institute of Allergy and Infectious Diseases, Bldg. 10, Rm. 11N311, 10 Center Dr., MSC 1892, Bethesda, MD 20892-1892. Tel:301-496-1904 Fax:301-496-0222 E-mail:rgermain{at}niaid.nih.gov.
Heat shock proteins (HSPs) derived from tumors or virally infected cells can stimulate antigen-specific CD8+ T cell responses in vitro and in vivo. Although this antigenicity is known to arise from HSP-associated peptides presented to the immune system by major histocompatibility complex (MHC) class I molecules, the cell biology underlying this presentation process remains poorly understood. Here we show that HSP 70 binds to the surface of antigen presenting cells by a mechanism with the characteristics of a saturable receptor system. After this membrane interaction, processing and MHC class I presentation of the HSP-associated antigen can occur via either a cytosolic (transporter associated with antigen processing [TAP] and proteasomedependent) or an endosomal (TAP and proteasomeindependent) route, with the preferred pathway determined by the sequence context of the optimal antigenic peptide within the HSP-associated material. These findings not only characterize two highly efficient, specific pathways leading to the conversion of HSP-associated antigens into ligands for CD8+ T cells, they also imply the existence of a mechanism for receptor-facilitated transmembrane transport of HSP or HSP-associated ligands from the plasma membrane or lumen of endosomes into the cytosol.
Key Words: immunology, vaccines, macrophages, T cells, peptides
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