Major histocompatibility complex class I-binding peptides are recycled to the cell surface after internalization.
Cytotoxic T lymphocytes (CTL) recognize target antigens as short, processed peptides bound to major histocompatibility complex class I (MHC-I) heavy and light chains (beta 2-microglobulin; beta 2-m). The heavy chain, which comprise the actual peptide binding alpha-1 and alpha-2 domains, can exist at the cell surface in different forms, either free, bound to beta 2-m or as a ternary complex with beta 2-m and peptides. MHC-I chains are also known to internalize, and recycle to the cell surface, and this has been suggested to be important in peptide presentation. Whether MHC-I-bound peptides also can recycle is not known. We have investigated this by using both peptide transporter mutant RMA-S cells and EL4 cells loaded with Db-binding peptides, by two different approaches. First, peptides were covalently linked with galabiose (Gal alpha 4Gal) at a position which did not interfere with Db binding or immunogenicity, and peptide recycling tested with Gal2-specific monoclonal antibodies. By flow cytometry, a return of Gal2 epitopes to the cell surface was found, after cellular internalization and cell surface clearance by pronase treatment. This peptide recycling could be discriminated from free fluid-phase uptake and was inhibited by methylamine, chloroquine and low temperature (18 degrees C) but not by leupeptin. Second, specific CTL were reacted with peptide-loaded target cells after complete removal of surface Db molecules by pronase, and after different times of incubation at 37 degrees C to allow reexpression. By this procedure, reappearance of target cell susceptibility was confirmed. The results are in agreement with a model for optimizing peptide presentation by recycling through an intracellular compartment similar to early endosomes in certain antigen-presenting cells.
Abdel Motal
U M
UM
Department of Immunology, Karolinska Institute, Stockholm, Sweden.
Zhou
X
X
Joki
A
A
Siddiqi
A R
AR
Srinivasa
B R
BR
Stenvall
K
K
Dahmén
J
J
Jondal
M
M
D000595:Amino Acid Sequence; D000818:Animals; D017951:Antigen Presentation; D002240:Carbohydrate Sequence; D002478:Cells, Cultured; D004187:Disaccharides / Q000378:metabolism; D006020:Glycopeptides / Q000378:metabolism*; D015395:Histocompatibility Antigens Class I / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000378:metabolism; D013602:T-Lymphocytes, Cytotoxic / Q000378:metabolism; D001613:beta 2-Microglobulin / Q000378:metabolism
D004187:Disaccharides; D006020:Glycopeptides; D015395:Histocompatibility Antigens Class I; D010446:Peptide Fragments; D001613:beta 2-Microglobulin; C032103:4-O-alpha-D-galactopyranosyl-D-galactose