Comparative immunoproteomics of Campylobacter jejuni in acute campylobacteriosis and asymptomatic individuals.

Campylobacter jejuni is a leading cause of bacterial gastroenteritis worldwide; however, the molecular determinants associated with symptomatic infection remain incompletely understood. In this study, an immunoproteomic approach was applied to characterize the antigenic landscape of C. jejuni during acute campylobacteriosis and to identify infection-associated proteins targeted by the human humoral immune response. Sera from patients with laboratory-confirmed acute campylobacteriosis (Group A) and asymptomatic individuals without recent gastrointestinal disease (Group B) were used to immunocapture bacterial proteins, followed by nano-liquid chromatography-tandem mass spectrometry analysis. A total of 418 and 517 immunoreactive proteins were identified in Groups A and B, respectively, with a large shared core repertoire, indicating extensive background immune recognition of conserved bacterial components. Functional annotation revealed that metabolic enzymes and ribosomal proteins dominated the immunoproteome in both groups. However, semi-quantitative emPAI analysis identified selective differences associated with acute infection. Group A sera preferentially recognized proteins involved in stress response, motility, secretion, and virulence-related functions, whereas Group B sera predominantly recognized housekeeping proteins. Bioinformatic prediction and network analyses identified immunoreactive proteins with features compatible with secretion-associated virulence factors, including proteins related to the flagellar export apparatus and the cytolethal distending toxin complex. Additionally, several immunoreactive proteins carried C-terminal acidic E-Block-like motifs previously described in Type IV secretion system effectors from other bacterial pathogens. Although the present approach does not directly demonstrate secretion, surface exposure, or translocation of the predicted proteins, these findings provide insight into infection-associated immune recognition patterns and identify candidate virulence-associated antigens that warrant future experimental validation.