Endocytic Recycling is Required for the Presentation of an Exogenous Peptide via MHC Class II Molecules (original) (raw)
Related papers
High efficiency of endogenous antigen presentation by MHC class II molecules
International Immunology, 1992
MHC class II molecules are Involved in the presentation of both exogenous and endogenous antigens to CD4 T cells. Using the trans-membrane hemagglutinin (HA) from measles virus and the secreted hen egg lysozyme (HEL) as antigen models, we have compared the efficiency of MHC class II presentation by naive antigen presenting cells (APCs) pulsed with exogenous antigen with that of their transfected counterparts synthesizing endogenous antigen. B cells expressing even a very low amount of trans-membrane HA were found to present endogenous HA to I-E d restricted T cell hybrldomas with a high efficiency whereas their naive counterparts required to be pulsed with a comparatively high amount of exogenous HA. Similarly, MHC class II presentation of endogenous secreted HEL was found to be much more efficient when compared with that of exogenous HEL. Biochemical studies did not reveal any enhanced intracellular degradation of endogenous HEL. As expected, HEL was released in the surrounding medium within <1 h. MHC class II presentation of endogenous HEL could not be explained by re-uptake by bystander APCs of HEL secreted In the surrounding medium. No sensitlzatlon of naive APCs could be observed either when co-cultured with HEL secreting cells or when cultured for 10 days with a sub-threshold amount of exogenous HEL. At the cell surface, I-E d molecules immunopreclpitated from HEL secreting cells were found to be slightly enriched In SDS-reslstant forms. These data raised the question of how peptides derived from endogenous transmembrane and secreted antigens can so efficiently reach an MHC class II loading compartment.
Peptides bind cell surface MHC class II proteins to yield complexes capable of activating CD4(+) T cells. By contrast, protein Ags require internalization and processing by APC before functional presentation. Here, T cell recognition of a short peptide in the context of class II proteins occurred only after delivery of this ligand to mature endosomal/lysosomal compartments within APC. Functional and biochemical studies revealed that a central cysteine within the peptide was cysteinylated, perturbing T cell recognition of this epitope. Internalization and processing of the modified epitope by APC, was required to restore T cell recognition. Peptide cysteinylation and reduction could occur rapidly and reversibly before MHC binding. Cysteinylation did not disrupt peptide binding to class II molecules, rather the modified peptide displayed an enhanced affinity for MHC at neutral pH. However, once the peptide was bound to class II proteins, oxidation or reduction of cysteine residues was severely limited. Cysteinylation has been shown to radically influence T cell responses to MHC class I ligands. The ability of professional APC to reductively cleave this peptide modification presumably evolved to circumvent a similar problem in MHC class II ligand recognition.
Journal of Cell Science, 2004
The location of antigens in distinct intracellular compartments of antigen-presenting cells (APCs) influences their proteolytic processing as well as access to major histocompatibility complex (MHC) molecules and presentation to T cells. MHCI and MHCII molecules are directed to different intracellular compartments for sampling peptide antigens (Neefjes et al., 1990; Peters et al., 1991). It is probable that pathways by which MHC molecules acquire peptides will have a significant impact on generation of peptide diversity that will be ultimately sensed by the T cell receptor. Thus, understanding the pathways involved in peptide generation and loading is an extremely important issue from an immunological perspective. This is especially relevant for the dissection of the mechanism of generation of an immune response against foreign proteins and development of tolerance against self proteins. Peptides generated in the cytosol by proteasomal degradation are generally thought to be presented on MHCI. These peptides are first transported across the endoplasmic reticulum (ER) membrane by the transporter associated with presentation (TAP), for loading on to MHCI in the ER lumen (Rock and Goldberg, 1999; York and Rock, 1996). Peptide-MHCI interaction is expected to take place during MHCI assembly, and is required for MHCI export out of the ER (Cresswell et al., 1999). In contrast, the generation and loading of peptides on MHCII molecules which present to the other class of T cells, namely the CD4 T cells, is believed to take place in endosomes and involves peptides derived from proteins and other antigens delivered from the outside via endocytic mechanisms. The apparent dichotomy between the sources of peptides for loading onto MHCI and MHCII is reinforced because newly synthesized MHCII molecules are protected from peptide loading in the ER and Golgi by the invariant chain (Ii) (Cresswell, 1994; Cresswell, 1996) which also sorts associated MHCII molecules from the Golgi to endolysosomal compartments (Bakke and Dobberstein, 1990). Immunocytochemistry, subcellular fractionation and immunoelectron microscopy approaches have identified MIIC or CIIVs as the canonical loading compartments for newly synthesized MHC class II (Neefjes, 1999; Peters et al., 1991). These are sites where MHCII molecules accumulate, and it is often argued that MIICs (or CIIVs) are a collection of late endocytic compartments that contain the necessary proteins for efficient peptide loading of MHCII molecules (Geuze, 1998; Neefjes, 1999). It is in the acidic milieu of these endosomal compartments that Ii-peptide exchange is facilitated by the endosomally localized peptide exchange catalyst H-2M in mice or HLA-DM in humans (Martin et al., 1996; Miyazaki et al., 1996). Peptide-MHCII complexes may also be generated when cell surface MHCII molecules recycle 4219 Antigen-presenting cells (APCs) are expected to present peptides from endocytosed proteins via major histocompatibility complex (MHC) class II (MHCII) molecules to T cells. However, a large proportion of peptides purified from MHCII molecules are derived from cytosolic self-proteins making the pathway of cytosolic peptide loading onto MHCII of critical relevance in the regulation of immune self-tolerance. We show that peptides derived from cytoplasmic proteins either introduced or expressed in the cytoplasm are first detectable as MHCIIpeptide complexes in LAMP-1 + lysosomes, prior to their delivery to the cell surface. These peptide-MHC complexes are formed in a variety of APCs, including peritoneal macrophages, dendritic cells, and B cells, and are able to activate T cells. This process requires invariant chain (Ii)-dependent sorting of MHCII to the lysosome and the activity of the molecular chaperone H-2M. This pathway is independent of the ER resident peptide transporter complex TAP and does not take place by cross-presentation from neighbouring cells. In conjunction with our earlier results showing that these peptides are derived by cytosolic processing via the proteasome, these observations provide evidence for a ubiquitous route for peptide transport into the lysosome for the efficient presentation of endogenous and cytoplasmic proteins to CD4 T cells.
European Journal of Immunology, 1993
Cytotoxic T lymphocytes (CTL) recognize target antigens as short, processed peptides bound to major histocompatibility complex class I (MHC-I) heavy and light chains (p2-microglobulin; P2-m). The heavy chain, which comprise the actual peptide binding a-1 and a-2 domains, can exist at the cell surface in different forms, either free, bound to PZ-m or as a ternary complex with 62-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 (Gala4Gal) at a position which did not interfere with Db binding or immunogenicity, and peptide recycling tested with Gal*-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°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°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.
Immunology, 2005
Soluble and particulate antigens are enzymatically degraded in acidic endocytic compartments of a variety of antigen-presenting cell (APC) types to generate antigenic peptides that load newly synthesized major histocompatibility class II (MHC-II) molecules, constituting a so-called classical MHC-II-restricted antigen presentation pathway. 1-3 MHC-II molecules on the surface of APC can also directly bind and present extracellular peptide epitopes 4 and chemically or enzymatically fragmented proteins, 5 as well as some denatured intact proteins 6-10 constituting an alternative MHC-II-restricted antigen presentation pathway. 11 Moreover, cell surface MHC-II molecules can be directly loaded with some native proteins in which epitopes are located in structurally flexible regions. 12,13
Traffic, 2000
We have developed cell-based cancer vaccines that activate anti-tumor immunity by directly presenting endogenously synthesized tumor antigens to CD4 + T helper lymphocytes via MHC class II molecules. The vaccines are non-conventional antigen-presenting cells because they express MHC class II, do not express invariant chain or H-2M, and preferentially present endogenous antigen. To further improve therapeutic efficacy we have studied the intracellular trafficking pathway of MHC class II molecules in the vaccines using endoplasmic reticulumlocalized lysozyme as a model antigen. Experiments using endocytic and cytosolic pathway inhibitors (chloroquine, primaquine, and brefeldin A) and protease inhibitors (lactacystin, LLnL, E64, and leupeptin) indicate antigen presentation depends on the endocytic pathway, although antigen degradation is not mediated by endosomal or proteasomal proteases. Because H2-M facilitates presentation of exogenous antigen via the endocytic pathway, we investigated whether transfection of vaccine cells with H-2M could potentiate endogenous antigen presentation. In contrast to its role in conventional antigen presentation, H-2M had no effect on endogenous antigen presentation by vaccine cells or on vaccine efficacy. These results suggest that antigen/MHC class II complexes in the vaccines may follow a novel route for processing and presentation and may produce a repertoire of class II-restricted peptides different from those presented by professional APC. The therapeutic efficacy of the vaccines, therefore, may reside in their ability to present novel tumor peptides, consequently activating tumor-specific CD4 + T cells that would not otherwise be activated.
Molecular Immunology, 2013
Major Histocompatibility Class I (MHC-I) molecules are present at the cell surface either as fully conformed trimolecular complexes composed of heavy chain, beta-2-microglobulin (2m) and antigenic peptide or as various open forms, devoid of the peptide and/or 2m. While the role of fully conformed MHC-I is well studied, the physiological role of open conformers is neglected. We have shown that fully conformed MHC-I and open MHC-I conformers segregate at the PM and during endosomal trafficking resulting in the exclusion of open MHC-I from the early endosomal/juxtanuclear recycling route. As a result, open MHC-I conformers are internalized with a higher rate than fully conformed counterparts. Although the majority of internalized open MHC-I is directed into the acidic late endosomal (LE) compartments, only a fraction of them is degraded. Namely, a significant fraction of open MHC-I is present in a subset of LEs with the capacity of recycling and/or exocytosis. Therefore, it should be examined whether exogenous peptide loading may occur during traveling of MHC-I proteins through LE compartments, especially in a subset of less acidic LEs that detach from the core of perinuclear acidic LEs and migrate toward the cell periphery. Given that the acidic LE environment is not favorable for peptide loading, an endosomal compartment with the recycling capacity and less acidic environment that allows stabilization of newly formed trimolecular complexes is proper site for exogenous peptide loading. We propose that a LE compartment which collect and retain open MHC-I conformers should be taken into consideration as a site of exogenous peptide loading.