Clathrin-coated lattices and buds on MHC class II compartments do not selectively recruit mature MHC-II

Georg Ramm, Leslie Pond, Colin Watts, Willem Stoorvogel

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Newly synthesized major histocompatibility complex class II molecules (MHC-II) are transported to MHC-II-containing endosomal and lysosomal compartments (MIICs) for the degradation of associated invariant chain and peptide loading. Subsequently MHC-II is transported to the plasma membrane, in part through direct fusion of MIICs with the plasma membrane. In search of potential alternative pathway(s) we studied the 3-dimensional structure of MIICs and the subcellular distribution of MHC-II by immuno electronmicroscopy on whole-mount preparations and cryosections of Mel JuSo cells. Intracellular MHC-II and invariant chain mainly localized to lamp-1 positive compartments suggesting that the majority of MHC-II exits the endocytic tract at lysosomes. Clathrin-coated lattices and buds were found to be associated with these organelles, but MHC-II was not found to be enriched in the clathrin-coated domains. Moreover, leupeptin, a drug that interferes with Ii-processing and delays delivery of newly synthesized MHC-II to the plasma membrane, was not found to decrease the relative amount of MHC-II in clathrin-coated areas. Together these data indicate clathrin-mediated exit site(s) from lysosomes but suggest that they do not selectively recruit mature MHC-II, consistent with the notion that transport to the plasma membrane occurs independently of the cytoplasmic domains of the MHC-II α and β chains.

Original languageEnglish
Pages (from-to)303-313
Number of pages11
JournalJournal of Cell Science
Issue number2
Publication statusPublished - 2000
Externally publishedYes


  • Clathrin
  • MHC class II compartment
  • MHC-II
  • MIIC lysosome

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