A reductionist cell-free major histocompatibility complex class II antigen processing system identifies immunodominant epitopes

Immunodominant epitopes are few selected epitopes from complex antigens that initiate T cell responses. Here, to provide further insights into this process, we use a reductionist cell-free antigen processing system composed of defined components. We use the system to characterize steps in antigen processing of pathogen-derived proteins or autoantigens and we find distinct paths for peptide processing and selection. Autoantigen-derived immunodominant epitopes are resistant to digestion by cathepsins, whereas pathogen-derived epitopes are sensitive. Sensitivity to cathepsins enforces capture of pathogen-derived epitopes by Major Histocompatibility Complex class II (MHC class II) prior to processing, and resistance to HLA-DM-mediated-dissociation preserves the longevity of those epitopes. We show that immunodominance is established by higher relative abundance of the selected epitopes, which survive cathepsin digestion either by binding to MHC class II and resisting DM-mediated-dissociation, or being chemically resistant to cathepsins degradation. Non-dominant epitopes are sensitive to both DM and cathepsins and are destroyed.

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“…18,22 Contradictory to CII predigestion data, nearly all rHA1-derived peptides were degraded by pre-exposure to cathepsins for 3h (Fig. 4a).…”

Section: Resultsmentioning

confidence: 87%

“…18 The system includes soluble purified HLA-DR (DR), CatB, CatH, and CatS that process protein antigens into peptides, and DM. Mass spectrometry is used for sequencing the unique peaks derived from each protein.…”

Section: Introductionmentioning

confidence: 99%

Divergent paths for the selection of immunodominant epitopes from distinct antigenic sources

et al. 2014

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“…Instead, DM acts as a peptide editor to catalyze the exchange of CLIP and other peptides onto MHC II during antigen presentation (8–10). We and other researchers have shown that DM-mediated peptide exchange plays a key role in epitope selection by favoring the presentation of peptides with higher kinetic stability (12, 15–17, 23, 24). DM deficiency results in predominant accumulation of MHC II-CLIP complexes at the cell surface and defective peptide loading and exchange, leading to defective negative selection, increased self-reactivity and immunodeficiency (25–27).…”

Section: Introductionmentioning

confidence: 94%

Evaluating the Role of HLA-DM in MHC Class II–Peptide Association Reactions

Yin

Maben

Becerra

et al. 2015

The Journal of Immunology

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Antigen presentation by major histocompatibility complex class II molecules (MHC II) to CD4+ T cells plays a key role in the regulation of the adaptive immune response. Loading of antigenic peptides onto MHC II is catalyzed by HLA-DM (DM), a non-classical MHC II molecule. The mechanism of DM-facilitated peptide loading is an outstanding problem in the field of antigen presentation. In this study we systemically explored possible kinetic mechanisms for DM-catalyzed peptide association, by measuring real time peptide association kinetics using fluorescence polarization assays and comparing the experimental data with numerically modeled peptide association reactions. We found that DM does not facilitate peptide association by stabilizing peptide-free MHC II against aggregation. Moreover, DM does not promote transition of an inactive peptide-averse conformation of MHC II to an active peptide-receptive conformation. Instead, DM forms an intermediate with MHC II that binds peptide with faster kinetics than MHC II in the absence of DM. In the absence of peptides, interaction of MHC II with DM leads to inactivation and formation of a peptide-averse form. This study provides novel insights into how DM efficiently catalyzes peptide loading during antigen presentation.

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“…A similar methodology that was used to identify T cell epitopes presented by HLA-DR1 was recently described (33). In this study a system for cell-free Ag processing was established.…”

Section: Discussionmentioning

confidence: 99%

HLA-DQ Molecules as Affinity Matrix for Identification of Gluten T Cell Epitopes

Dørum

Bodd

Fallang

et al. 2014

The Journal of Immunology

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Even though MHC class II is a dominant susceptibility factor for many diseases, culprit T cell epitopes presented by disease-associated MHC molecules remain largely elusive. T cells of celiac disease lesions recognize cereal gluten epitopes presented by the disease-associated HLA molecules DQ2.5, DQ2.2, or DQ8. Employing celiac disease and complex gluten Ag digests as a model, we tested the feasibility of using DQ2.5 and DQ2.2 as an affinity matrix for identification of disease-relevant T cell epitopes. Known gluten T cell epitope peptides were enriched by DQ2.5, whereas a different set of peptides was enriched by DQ2.2. Of 86 DQ2.2-enriched peptides, four core sequences dominated. One of these core sequences is a previously known epitope and two others are novel epitopes. The study provides insight into the selection of gluten epitopes by DQ2.2. Furthermore, the approach presented is relevant for epitope identification in other MHC class II–associated disorders.

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A reductionist cell-free major histocompatibility complex class II antigen processing system identifies immunodominant epitopes

Cited by 59 publications

References 37 publications

Divergent paths for the selection of immunodominant epitopes from distinct antigenic sources

Divergent paths for the selection of immunodominant epitopes from distinct antigenic sources

Evaluating the Role of HLA-DM in MHC Class II–Peptide Association Reactions

HLA-DQ Molecules as Affinity Matrix for Identification of Gluten T Cell Epitopes

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