Characterization of HLA Class II/Peptide-TCR Interactions of the Immunodominant T Cell Epitope in Art v 1, the Major Mugwort Pollen Allergen

Abstract

More than 95% of mugwort pollen-allergic individuals are sensitized to Art v 1, the major allergen in mugwort pollen. Interestingly, the CD4 T cell response to Art v 1 involves only one single immunodominant peptide, Art v 125–36 (KCIEWEKAQHGA), and is highly associated with the expression of HLA-DR1. Therefore, we investigated the molecular basis of this unusual immunodominance among allergens. Using artificial APC expressing exclusively HLA-DRB1*0101 and HLA-DRA*0101, we formally showed that DR1 acts as restriction element for Art v 125–36-specific T cell responses. Further assessment of binding of Art v 125–36 to artificial HLA-DR molecules revealed that its affinity was high for HLA-DR1. Amino acid I27 was identified as anchor residue interacting with DR molecules in pocket P1. Additionally, Art v 125–36 bound with high affinity to HLA-DRB1*0301 and *0401, moderately to HLA-DRB1*1301 and HLA-DRB5*0101, and weakly to HLA-DRB1*1101 and *1501. T cell activation was also inducible by Art v 125–36-loaded, APC-expressing HLA molecules other than DR1, indicating degeneracy of peptide binding and promiscuity of TCR recognition. Specific binding of HLA-DRB1*0101 tetramers containing Art v 119–36 allowed the identification of Art v 125–36-specific T cells by flow cytometry. In summary, the immunodominance of Art v 125–36 relies on its affinity to DR1, but is not dictated by it. Future investigations at the molecular HLA/peptide/TCR and cellular level using mugwort pollen allergy as a disease model may allow new insights into tolerance and pathomechanisms operative in type I allergy, which may instigate new, T cell-directed strategies in specific immunotherapy.

Association of HLA-DR1 with the allergic response to the major mugwort pollen allergen: molecular background

“…Although the T cell response to Art v 1 25-36 is clearly associated with HLA-DR1, we previously found Art v 1 25-36 –specific T cells restricted by HLA-DR3, -DR16 or -DR15 in the minor fraction of DR1-negative patients [10]. Accordingly, the peptide showed degenerate high affinity binding to several HLA-DR alleles [10].…”

Modulation of allergen-specific T-lymphocyte function by virus-like particles decorated with HLA class II molecules

“…14 Using a large panel of Art v 1-specific T-cell lines generated from peripheral blood (PB) of patients with mugwort allergy, we have identified a single immunodominant epitope, Art v 1 [25][26][27][28][29][30][31][32][33][34][35][36] , that is preferentially presented by HLA-DRB1*01. [15][16][17] Moreover, we have recently cloned and characterized an Art v 1-specific T-cell receptor (TCR), which allows us to investigate cell fate and phenotype decisions in PB T cells of individuals without allergy instead of using repeatedly stimulated T-cell lines or clones from individuals with allergy. 18 To the best of our knowledge, this is the first description of artificially induced, HLA class II restricted microvesicles (VLPs) able to modulate allergen-specific T-lymphocyte responses.…”

Distorted Immunodominance by Linker Sequences or other Epitopes from a Second Protein Antigen During Antigen-Processing

“…Over the last decades, many studies have aimed to unravel the mechanisms of immunodominance. Among the hypotheses considered are intrinsic structural features of protein antigens12345, sensitivity to proteases67891011, epitope affinity for MHC class II12, T cell precursor frequency13, T cell receptor affinity for peptide/MHC II14151617, contributions from HLA-DM or H-2M in mice (DM, from now on)18192021, and contributions from HLA-DO or H-2O in mice (DO, from now on)222324. However, due to the complexity of the antigen processing pathway, pointing to a single mechanism as the driving force behind immunodominance has proved difficult.…”