Immuno-informatic Prediction of B and T cell Epitopes of Cysteine Protease Allergen from Phaseolus vulgaris with Cross-reactive Potential and Population Coverage

Abstract

Background: In-silico mapping of epitopes by immune-informatics has simplified the efforts towards understanding antigen-antibody interactions. The knowledge of allergen epitopes may help in advancing the diagnosis and therapy of allergic diseases.

Objective: This study was intended to identify B and T cell epitopes of cysteine protease allergen of Phaseolus vulgaris.

Methods: Modeller 9v20 software was used for the generation of three-dimensional model of cysteine protease and quality assessment was performed using SAVES webserver and other in silico software. Linear and conformational B and T cell epitopes were predicted via immuno-informatics based computational servers. Epitopes were synthesized and their immunoreactivity was analyzed using specific IgE ELISA with food allergy positive patient's sera. Cellular immune response of peptides was determined through basophil activation assay. Consurf and SDAP (property distance) were used to examine the evolutionary conservancy and potential cross-reactivity of predicted epitopes. MSA based positional conservancy between HDM allergen epitopes and predicted peptides was also established using IEDB epitope database. Finally, population coverage for each promiscuous T cell epitope was predicted using IEDB population coverage analysis tool.

Results: Cysteine protease structure was derived by homology modeling and combination of bioinformatic tools predicted three B- and three T-cell peptides by consensus method and validated computationally. ELISA with kidney bean sensitive patient's sera showed higher IgE binding of B-cell peptides as compared to T-cell or control peptides. Epitope conservancy revealed B-cell epitopes being upto 95% conserved in comparison to variable T-cell epitopes (upto 69%). B-cell peptides were crossreactive with homologous allergens based on PD values. Structural comparison of cysteine protease with Der p 1 and Der f 1 showed similar epitopic regions, validating the prediction accuracy of epitopes. Promiscuous T-cell epitopes binding to broad-spectrum class-II MHC alleles demonstrated the distribution of T-cell peptides world-wide (30-98%) and in Asian population (99%).

Conclusion: The current approach can be applied for identification of epitopes. Analysis of crossreactive and widely-distributed specific epitopes of allergen and knowledge about their interactive surfaces will help in understanding of food allergy and related immune responses.

Keywords: Cysteine protease; Homology modeling; IgE binding and promiscuous T-cell peptides; Phaseolus vulgaris; basophil activation test; crossreactivity.