Presentation by Recycling MHC Class II Molecules of an Influenza Hemagglutinin-Derived Epitope That Is Revealed in the Early Endosome by Acidification

Abstract

We investigated the roles of nascent and recycling MHC class II molecules (MHC II) in the presentation of two well-defined I-Ed-restricted epitopes that are within distinct regions of the influenza virus hemagglutinin (HA) protein. The site 3 epitope (S3; residues 302–313) lies in the stalk region that unfolds in response to mild acidification, while the site 1 epitope (S1; residues 107–119) is situated in the stable globular domain. In a murine B lymphoma cell line and an I-Ed-transfected fibroblast cell line, presentation from inactivated virus of S3 is inhibited by primaquine, a compound that prevents recycling of cell surface proteins, including MHC II, while S1 presentation is unaffected. In contrast, brefeldin A, an agent that inhibits exit of proteins from the endoplasmic reticulum, selectively inhibited S1 presentation without affecting S3 presentation, suggesting that S1 presentation requires nascent MHC II. The use of agents that perturb endosomal function revealed a requirement for acidification of internalized viral particles for presentation of both epitopes. Notably, all compounds tested had similar effects on presentation of the two epitopes derived from endogenously synthesized HA. Thus, recycling I-Ed molecules appear to be crucial for capturing and presenting an epitope that is revealed in mild acidic conditions following the uptake of virions or the synthesis of Ag, while nascent I-Ed molecules are required for presentation of a second epitope located in a structurally constrained region of the same polypeptide. Viral glycoproteins, such as HA, may have been a major impetus for the evolutionary establishment of this recycling pathway.

In Vivo, Dendritic Cells Can Cross-Present Virus-Like Particles Using an Endosome-to-Cytosol Pathway

“…The lack of inhibition of PPV-VLPs presentation by primaquin as well as the lack of colocalization of PPV-VLPs and rab11 strongly suggest that PPV-VLPs (or derived peptides) are not delivered into recycling vesicles, but remain in the endosomes to deliver the OVA 257-264 epitope into the cytosol. This conclusion is consistent with the inhibition of OVA 257-264 presentation in the presence of BFA, which inhibits protein transport (including nascent MHC class I molecules) from the ER, without affecting recycling MHC class I and II molecules (65), showing that OVA 257-264 presentation is mediated by neosynthesized MHC class I molecules. After uptake, PPV-VLPs are localized in late endosomal compartments.…”

Differential MHC class II component expression in HPV‐positive cervical cancer cells: Implication for immune surveillance

“…Protein expression levels of components of the MHC class II presentation pathway, the stoichiometry of DMA/DMB complexes and the subcellular localization of these components may impact the successful editing of the peptide repertoire displayed to antigen-specific T cells. These data are in line with the observation that DMA/DMB expression and localization are responsible for successful editing of epitopes provided from auto-antigens, e.g., glutamate decarboxylase in the setting of autoimmune responses, 36 viral proteins 37 or the peptide reper- toire displayed by HLA-DR4 molecules. 18 Of note, neither lack of cathepsin D nor LFA-3 expression is apparently responsible for insufficient recognition of ME180 cells in the absence of IFN-g.…”

“…40,41 This has been corroborated in a murine model of influenza hemagglutinin epitopes: Some epitopes are dependent on the capture by recycled class II molecules, and a different epitope requires nascent MHC class II molecules for effective presentation. 37 A similar situation may be true for the DR4-presented epitope LFMDSLNFVCPWC 3 defined by the HPV68/E7-specific T-cell line used in our study. Either the DMA/DMB editing function 42 and the peptide repertoire generated by ME180 does not allow loading of this epitope on DR4 molecules in the absence of IFN-g or this epitope is dependent on the accessibility to specific MHC class II compartments.…”

Differential Processing of CD4 T-cell Epitopes from the Protective Antigen of Bacillus anthracis

“…Peptide epitopes liberated during processing usually bind newly synthesized MHC class II molecules optimally at low pH under the control of chaperones DM and DO following degradation of the invariant chain. Alternatively, epitopes in structurally flexible regions of protein antigens may bind mature MHC class II recycled from the APC surface in neutral or mildly acidic endosomal compartments (24,37). Further processing or "trimming" of exposed amino acids of the peptides already bound to MHC molecules can occur (38), mediated by enzymes such as the metalloproteinase aminopeptidase N (39).…”