IgE vs IgG4 epitopes of the peanut allergen Ara h 1 in patients with severe allergy

Background: Development and maintenance of tolerance to food allergens may be associated with increased levels of specific IgG4. It has been suggested that co-localisation of IgG4 and IgE binding epitopes may be of great significance for the tolerance, where IgG4 may act by blocking IgE binding to the allergen. However, recent studies have demonstrated the very importance of the IgG4-epitope affinity for the blocking ability. Studies comparing IgE and IgG4 binding epitopes mainly focus on the identification of linear epitopes.
Peanut allergy is one of the most severe and persistent forms of food allergy. The importance of conformational epitopes, of the major peanut allergen Ara h 1, has been demonstrated. The aim of this study was to compare Ara h 1-specific epitope patterns for IgE and IgG4 in patients with severe peanut allergy applying a method suitable to identify both linear and conformational epitopes.
Methods: Ara h 1-specific IgE and IgG4 epitope patterns were examined by competitive immunoscreening of a phage-displayed random 7-mer peptide library using polyclonal IgE and IgG4 from three individual patients suffering from severe peanut allergy. The resulting peptide sequences were mapped on the surface of a 3D model of the Ara h 1 molecule to mimic epitopes by the use of a computer-based algorithm.
Results: All identified epitope mimics corresponded to conformational epitopes. Each individual peanut allergic patient had his/her own distinct IgE as well as IgG4 epitope binding profile.
Although three motifs were identified for all three patients and accounted for half of all identified IgE epitope mimics, no consensus motifs were identified for IgG4. Even though the epitopes overlapped, the IgG4 binding epitope mimics were more heterogeneous than the IgE binding epitope mimics. In addition a higher epitope binding affinity for IgE than IgG4 was indicated.
Conclusion: This preliminary study using competitive immunoscreening of a phage-displayed peptide library successfully distinguished IgE binding patterns from IgG4 binding patterns. The method allows an identification of both, linear and conformational epitopes and gives information on the specificity, diversity and affinity of the identified epitope mimics. This could be a valuable tool to study the balance and dynamics of the antibody IgE- and IgG4-repertoire, and increase the knowledge and understanding of the mechanisms involved in the development of allergy and tolerance.