MHC Class I Endosomal and Lysosomal Trafficking Coincides with Exogenous Antigen Loading in Dendritic Cells

Abstract

BackgroundCross-presentation by dendritic cells (DCs) is a crucial prerequisite for effective priming of cytotoxic T-cell responses against bacterial, viral and tumor antigens; however, this antigen presentation pathway remains poorly defined.Methodology/Principal FindingsIn order to develop a comprehensive understanding of this process, we tested the hypothesis that the internalization of MHC class I molecules (MHC-I) from the cell surface is directly involved in cross-presentation pathway and the loading of antigenic peptides. Here we provide the first examination of the internalization of MHC-I in DCs and we demonstrate that the cytoplasmic domain of MHC-I appears to act as an addressin domain to route MHC-I to both endosomal and lysosomal compartments of DCs, where it is demonstrated that loading of peptides derived from exogenously-derived proteins occurs. Furthermore, by chasing MHC-I from the cell surface of normal and transgenic DCs expressing mutant forms of MHC-I, we observe that a tyrosine-based endocytic trafficking motif is required for the constitutive internalization of MHC-I molecules from the cell surface into early endosomes and subsequently deep into lysosomal peptide-loading compartments. Finally, our data support the concept that multiple pathways of peptide loading of cross-presented antigens may exist depending on the chemical nature and size of the antigen requiring processing.Conclusions/SignificanceWe conclude that DCs have ‘hijacked’ and adapted a common vacuolar/endocytic intracellular trafficking pathway to facilitate MHC I access to the endosomal and lysosomal compartments where antigen processing and loading and antigen cross-presentation takes place.

Endogenous viral antigen processing generates peptide-specific MHC class I cell-surface clusters

“…4A) and cell-surface segregation (Fig. 4B) This observation extends the function of the class I cytoplasmic domain, previously shown to be involved with class I plasma membrane internalization and endosomal trafficking (28)(29)(30)(31)(32)(33). Because the efficiency of K b loading with SIIN is not affected by the loss of the cytoplasmic tail, we infer that ΔK b properly associates with TAP and functions normally in the peptideloading complex.…”

Fcγ receptor antigen targeting potentiates cross-presentation by human blood and lymphoid tissue BDCA-3+ dendritic cells

“…by guest www.bloodjournal.org From early endosomes, 33,40 late endosomes or endo/lysosomes. [41][42][43] These phagosomes contain MHCI loading complex components. 36,37,40,44,45 To clarify mechanisms involved in BDCA-3 ϩ DC crosspresentation, we tested the involvement of endosomal and proteasomal processing, analogous to experiments described in Figure 2.…”

Long-Peptide Cross-Presentation by Human Dendritic Cells Occurs in Vacuoles by Peptide Exchange on Nascent MHC Class I Molecules

“…Mechanistic studies of the vacuolar pathway are limited. It is unclear whether MHC-I molecules used in the vacuolar pathway are recycled from the cell surface or are newly synthesized (13,(15)(16)(17)(18)(19). A10, which recognizes peptide MAGE-A3 168-176 presented by HLA-A1, was derived in-house (22).…”