Functional and ultrastructural evidence for intracellular formation of major histocompatibility complex class II-peptide complexes during antigen processing

Clifford V. Harding, Emil R. Unanue, Jan W. Slot, Alan L. Schwartz, Hans J. Geuze

Research output: Contribution to journalArticlepeer-review

71 Scopus citations

Abstract

Antigen presentation requires intracellular processing of native antigens to produce immunogenic peptides that bind to major histocompatibility complex class II (MHC-II) molecules. In functional studies of antigen processing by elicited peritoneal macrophages, MHC-II-peptide complexes were formed intracellularly. Immunogenic peptides were not released to bind surface MHC-II molecules. Ultrastructural studies employing immunogold staining in ultrathin cryosections of these macrophages showed large amounts of MHC-II molecules in intracellular sac-like vacuoles in the peripheral cytoplasm; most of these were negative for the lamp 1 lysosomal/endosomal membrane protein and cathepsin D. MHC-II molecules were also present in endosomes containing cathepsin D and lamp 1 as well as previously internalized gold-transferrin. The intracellular pool of MHC-II molecules was only slightly decreased by treatment with cycloheximide for 3 hr, indicating that it consisted mainly of endocytosed, recycling molecules, as opposed to nascent ones. These ultrastructural studies support the notion that there is endocytosis of MHC-II molecules into endocytic compartments, consistent with our earlier biochemical data. Furthermore, we have defined the distinct endocytic compartments that must mediate important functions in antigen processing, including the formation of MHC-II-peptide complexes.

Original languageEnglish
Pages (from-to)5553-5557
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume87
Issue number14
DOIs
StatePublished - 1990

Keywords

  • Endocytosis
  • Endosomes
  • Immunocytochemistry

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