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Peptide‐receptive class I major histocompatibility complex molecules on TAP‐deficient and wild‐type cells and their roles in the processing of exogenous antigens
Author(s) -
Rui Song,
Angel Porgador,
Clifford V. Harding
Publication year - 1999
Publication title -
immunology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.297
H-Index - 133
eISSN - 1365-2567
pISSN - 0019-2805
DOI - 10.1046/j.1365-2567.1999.00759.x
Subject(s) - brefeldin a , major histocompatibility complex , transporter associated with antigen processing , antigen processing , mhc class i , antigen presentation , mhc restriction , biology , antigen , microbiology and biotechnology , peptide , cytotoxic t cell , chemistry , biochemistry , immunology , in vitro , golgi apparatus , endoplasmic reticulum
These studies addressed the nature and origin of peptide‐receptive class I major histocompatibility complex (MHC‐I) molecules used to present exogenous antigens. Peptide‐receptive K b molecules in transporter for antigen presentation (TAP)1 −/− and TAP1 +/+ macrophages were quantitated by exposing cells to exogenous ovalbumin (OVA)(257–264) peptide and then measuring OVA(257–264):K b complexes with a T hybridoma assay or flow cytometry (using a complex‐specific antibody). Relative to TAP1 +/+ cells, TAP1 −/− cells had decreased levels of pre‐existing cell‐surface peptide‐receptive MHC‐I molecules at 37°. With continued exposure of viable cells to peptide, however, TAP1 −/− and TAP1 +/+ cells formed similar levels of OVA(257–264):K b complexes, suggesting that nascent labile MHC‐I molecules were captured and stabilized by exogenous peptide. Brefeldin A inhibited generation of OVA(257–264):K b complexes on TAP1 −/− (but not TAP1 +/+ ) cells at 37°, confirming the importance of a flux of unstable nascent MHC‐I molecules in TAP1 −/− cells at 37°. In contrast, at 26° both TAP1 −/− and TAP1 +/+ cells expressed brefeldin A‐resistant, peptide‐receptive MHC‐I molecules at similar levels. Alternate MHC‐I processing of exogenous particulate antigen correlated with ability to present exogenous peptide. Thus, processing was brefeldin A‐sensitive with TAP1 −/− macrophages at 37°, but brefeldin A‐resistant with TAP1 +/+ cells at 37°, as well as with TAP1 +/+ or TAP1 −/− cells at 26°. We conclude that alternate MHC‐I antigen processing normally utilizes pre‐existing MHC‐I molecules, but TAP1 −/− cells at 37° mainly use nascent MHC‐I molecules, because of a lack of pre‐existing, stable, peptide‐receptive MHC‐I molecules. The results support a vacuolar processing mechanism with binding of peptides to MHC‐I molecules in post‐Golgi compartments or on the cell surface.