Identification of antigenic epitopes of thyroperoxidase, thyroglobulin and interleukin-24. Exploration of cross-reactivity with environmental allergens and possible role in urticaria and hypothyroidism.

Chronic spontaneous urticaria is characterized by hives and angioedema that significantly affects quality of life. People with urticaria have higher self-reactive autoantibodies IgE and IgG than healthy people. Other proteins implicated in the pathogenesis of urticaria include thyroperoxidase (TPO), interleukin 24 (IL24) and thyroglobulin (Tg). The reason why these proteins are recognized by specific autoantibodies in people with urticaria is unknown.

The aim of this study was to compare the sequences of TPO, Tg and IL24 with some prevalent allergens through in silico analysis.

The amino acid sequences of IL24, TPO and Tg were compared between them and with 22 environmental allergens. To explore the degree of protein identity and cover, researchers carried out phylogenetic studies and multiple pairing. Proteins without 3D structure reported in the database were modelled and compared by homology. Residues conserved and accessible to the solvent were located in the 3D model to identify possible areas of cross-reactivity and antigen binding.

Five epitopes for TPO, six for IL24 and six for Tg were predicted with the 3D model built. The amino acid sequences of allergens from different sources (Dermatophagoides pteronyssinus, Blomia tropicalis, Betula verrucosa, Cynodon dactylon, Aspergillus fumigatus, Canis domesticus, Felis domesticus) were also compared with the human proteins. The cover and alignments between allergens and human proteins were low.

In conclusion, there are possible linear and conformational epitopes of TPo, Tg and IL24 that can be the target of IgE and IgG binding in patients with urticaria. These epitopes aren’t found in common allergens, which indicates that autoreactivity to the human proteins is not through cross-reactivity.