The pathway for MHCII-mediated presentation of endogenous proteins involves peptide transport to the endo-lysosomal compartment (original) (raw)
Related papers
How MHC class II molecules reach the endocytic pathway
The EMBO Journal, 1995
Communicated by H.Ploegh P.Benaroch and M.Yilla contributed equally to this study We have examined trafficking of major histocompatibility complex (MHC) class II molecules in human B cells exposed to concanamycin B, a highly specific inhibitor of the vacuolar H+-ATPases required for acidification of the vacuolar system and for early to late endosomal transport. Neutralization of vacuolar compartments prevents breakdown of the invariant chain (Ii) and blocks conversion of MHC class II molecules to peptide-loaded, SDS-stable a,l3 dimers. Ii remains associated with ac and this complex accumulates internally, as ascertained biochemically and by morphological methods. In concanamycin B-treated cells, a slow increase (>20-fold) in surface expression of Ii, mostly complexed with ac, is detected. This surface-disposed fraction of a4Ii is nevertheless a minor population that reaches the cell surface directly, or is routed via early endosomes as intermediary stations. In inhibitor-treated cells, the bulk of newly synthesized acIi is no longer accessible to fluid phase endocytic markers. It is concluded that the majority of aIli is targeted directly from the trans-Golgi network to the compartment for peptide loading, bypassing the cell surface and early endosomes en route to the endocytic pathway.
Trafficking of spontaneously endocytosed MHC proteins
Proceedings of the National Academy of Sciences, 1999
Class I MHC protein primarily presents endogenous antigen but also may present exogenous antigen. Here, we investigated the intracellular pathway of spontaneously internalized class I MHC protein by confocal microscopy. beta(2)-microglobulin (beta(2)m), labeled with a single fluorophore, was exchanged at the surface of B cell transfectants to specifically mark cell surface and endocytosed class I MHC protein. Intracellular beta(2)m colocalized with fluorophore-conjugated transferrin, implying that class I MHC protein endocytosed into early endosomes. These endosomes containing fluorescent beta(2)m were found close to or within the Golgi apparatus, marked by fluorescent ceramide. Even after 24 hr of incubation, very little fluorescent beta(2)m was found in intracellular organelles stained by DiOC(6), marking the endoplasmic reticulum, or fluorophore-conjugated low density lipoprotein, marking late endosomes and lysosomes. Fluorophore-conjugated superantigens (staphylococcal enterotoxin A and B), presumed to enter cells bound to class II MHC protein, also were found to endocytose into beta(2)m-containing early endosomes. Staining with mAb and use of transfectants expressing MHC protein attached to green fluorescent protein confirmed the presence of intracellular compartments rich in both class I and II MHC protein and demonstrated that class I and II MHC protein also colocalize in discrete microdomains at the cell surface. These cell surface microdomains also contained transferrin receptor and often were juxtaposed to cholesterol-rich lipid rafts. Thus, class I and II MHC protein meet in microdomains of the plasma membrane and endocytose into early endosomes, where both may acquire and present exogenous antigen.
Seminars in Immunology, 1995
Nascent class II MHC (MHC class II) molecules are transported from the ER to a specialized late endocytic antigen processing compartment, termed MIIC (MHC class II compartment). This compartment, with some variations, has been defined in multiple studies of B cells, macrophages and dendritic cells. Though this compartment shares properties with both lysosomes and late endosomes, it is a specialized compartment that differs from these other endocytic compartments in important characteristics. The MIIC contains abundant MHC class II molecules and other molecules important for antigen processing, including lysosomal enzymes and HLA-DM. Biochemical and functional immunological assays have detected not only the presence but the initial formation of peptide-MHC class II complexes in MIIC during the processing of certain model antigens. However, MHC class II molecules are also present in other endocytic compartments, albeit at lower levels, and these compartments may also perform antigen processing functions.
Traffic, 2000
Exogenous antigenic peptides captured and presented in the context of major histocompatibility (MHC) class II molecules on APC, have been employed as potent vaccine reagents capable of activating cellular immune responses. Binding and presentation of select peptide via surface class II molecules has been reported. Here, a role for endocytosis and early endosomes in the presentation of exogenous peptides via MHC class II molecules is described. T cell recognition of a 14 amino acid human serum albumin-derived peptide in the context of HLA-DR4 was observed only with metabolically active APC. The delayed kinetics and temperature dependence of functional peptide presentation via APC, were consistent with a requirement for peptide internalization to early endosomal compartments prior to T cell recognition. Ablating endocytosis by exposing cells to inhibitors of ATP production completely blocked the display of functional peptide:class II complexes on the surface of the APC. Presentation of the peptide was also found to be sensitive to primaquine, a drug that perturbs the recycling of transport vesicles containing endocytic receptors and mature class II complexes. Functional presentation of the endocytosed peptide was dependent upon these mature class II complexes, as inhibitor studies ruled out a requirement for newly synthesized class II molecules. N-terminal processing of the endocytosed peptide was observed upon trafficking through endosomal compartments and linked to the formation of functional peptide:class II complexes. These findings establish a novel mechanism for regulating class II-restricted peptide presentation via the endocytic pathway.