Immunopathogenic role of the HLA-B∗51:01-specific immunopeptidome in Behçet's disease.

OBJECTIVE: The immunopeptidome, the collection of peptides bound to human leukocyte antigens (HLAs), plays a key role in initiating immune responses. HLA-B∗51:01 is an allele associated with Behçet's disease (BD). However, the role of the immunopeptidome bound to HLA-B∗51:01 in the pathogenesis of BD remains unclear.

METHODS: We profiled the HLA-bound immunopeptidome using plasma samples from HLA-B∗51:01-positive BD and healthy controls (HCs). HLA-class I molecules were immunoprecipitated, and liquid chromatography-tandem mass spectrometry was performed to compare HLA-bound peptides between HLA-B∗51:01-positive BD with HCs. Potential HLA-B∗51:01-bound peptides, T cell epitopes, were then selected by the binding prediction software NetMHCpan. The immunogenicity of the selected peptides was investigated through enzyme-linked immunospot, flow cytometry, and dextramer staining.

RESULTS: We analyzed the immunopeptidome established from BD using two different methods. First, BD-specific peptides were identified. Among 8008 peptides, 2306 were found only in BD patients. The BD-specific immunopeptidome preferred hydrophobic amino acids at position 2. Exome sequencing confirmed the presence of the identified representative peptides. These peptides, when presented on monocyte-derived dendritic cells from HLA-B∗51:01-positive BD patients, effectively activated T cells, causing them to secrete proinflammatory cytokines and express the degranulation marker CD107a. Additionally, BD-predominant peptides were identified, whose amount was increased in BD than in HC. BD-predominant peptides also activated T cells, leading to the secretion of proinflammatory cytokines.

CONCLUSION: The immunopeptidome presented on HLA-B∗51:01-positive BD is distinct from that of HLA-B∗51:01-positive HCs and can activate T cells and secrete proinflammatory cytokines; this may contribute to the pathogenesis of BD.