Allergen-peptide-MHC class II complex (pMHCII)

The allergen-peptide-MHC class II (pMHCII) complex is a fundamental molecular assembly on the surface of antigen-presenting cells (APCs) that dictates the specificity of the adaptive immune response in allergic diseases (Larche et al., 2006, Nature Reviews Immunology). It consists of a processed fragment of an allergen (the T-cell epitope) non-covalently bound within the peptide-binding groove of a Major Histocompatibility Complex (MHC) class II molecule, such as HLA-DR, HLA-DQ, or HLA-DP (Uniprot P01903, P01911). This complex is specifically recognized by the T-cell receptor (TCR) of CD4+ T cells, which, in allergic individuals, typically triggers a Type 2 helper (Th2) immune response characterized by IgE production and eosinophilic inflammation (Wambre et al., 2017, Science Translational Medicine). As a therapeutic target, this complex is utilized in peptide-based immunotherapy (PIT), where synthetic peptides representing dominant T-cell epitopes are administered to induce immunological tolerance. By engaging the TCR-pMHCII interaction without the conformational epitopes required for IgE cross-linking, these therapies aim to reprogram the immune system toward a regulatory or non-responsive state (anergy), thereby reducing the clinical symptoms of allergy and asthma (Larche et al., 2006, Nature Reviews Immunology). Key challenges for drugs targeting this complex include MHC restriction, where the therapeutic peptide must match the patient's specific HLA alleles to be effective, and the risk of late-phase T-cell mediated reactions (Creticos et al., 2014, JACI).

Other names

Allergen-pMHCII complexT-cell epitope-MHC II complexAntigen-MHC II complexAllergen-derived peptides bound to MHC class II and recognized by allergen-specific T cell receptors

Induction of T cell anergy, deletion of pathogenic Th2 cells, and promotion of regulatory T cell (Treg) differentiation through the presentation of specific T-cell epitopes in a non-inflammatory context (Larche et al., 2006).