Allele-Skewed HLA-DR Immunopeptidomes of Bordetella pertussis

Background/Objectives: Infection with Bordetella pertussis causes whooping cough. CD4+ T cell responses depend on bacterial peptides displayed by HLA class II, yet allele- and strain-resolved maps of naturally processed B. pertussis HLA-DR ligands remain limited. We sought to define which antigens yield HLA-DR ligands in a human macrophage model and whether presentation is skewed by HLA-DR molecule and bacterial strain. Methods: THP-1–derived macrophages were pulsed with whole-cell lysates of B. pertussis vaccine/reference strain Tohama I or clinical isolate D420. HLA-DR was immunoaffinity purified; eluted peptides were identified by LC-MS/MS and assigned to HLA-DR molecules encoded by HLA-DRB1*01:01, HLA-DRB1*15:01, and HLA-DRB5*01:01. Results: We identified 63 B. pertussis peptide ligands from 29 source proteins. Presentation was skewed by HLA-DR molecule: DRB1*01:01 accounted for 37 ligands from 21 antigens, DRB1*15:01 for 22 from 7, and DRB5*01:01 for 4 from 4. Most source proteins contributed ligands primarily to one HLA-DR molecule, so an antigen that supplies peptides to one DR product need not supply peptides to another. Strain further partitioned the ligandome: 32 ligands unique to Tohama I, 12 to D420, and only 19 from 8 proteins with both lysates. Only three antigens contributed ligands to both DRB1*01:01 and DRB1*15:01; two of these, pertactin and filamentous hemagglutinin, are components of current acellular pertussis vaccines. Conclusions: B. pertussis HLA-DR ligandomes are jointly shaped by bacterial strain and HLA-DR molecule. Antigens can interact selectively with individual HLA-DR products, and peptides from a given antigen may be recovered after pulse with one strain but not another. These findings support HLA-DR and strain-aware interpretation of class II presentation and nominate BrkA autotransporter (Bordetella resistance to killing A), outer membrane protein A (OmpA), tracheal colonization factor (TcfA), and a divalent metal transporter (DMT) family transporter for follow-up.