Csep1P protein from Campylobacter concisus induces a chemokine-dominant inflammatory state in macrophages and enhances proinflammatory response to gut bacteria

Translocation of Campylobacter concisus from the oral cavity to the intestinal tract is increasingly recognised as a contributor to inflammatory bowel disease (IBD). The C. concisus secreted protein Csep1 has emerged as a molecular marker of C. concisus strains associated with Crohn’s disease, a form of IBD. However, its structure and role in inflammation remain unknown. Here, we report the X-ray crystal structure of plasmid-encoded Csep1 P that reveals a unique α-helical fold with structural similarity to Helicobacter pylori cysteine-rich proteins HcpB and HcpC. Because HcpA, another Hcp family member, is known to affect monocyte differentiation, this structural similarity led us to hypothesise that Csep1 P may modulate monocyte differentiation and macrophage function. Transcriptomic analysis revealed that Csep1 P induced a chemokine-dominant inflammatory state in macrophages, M1-chem. Protein-level validation in both THP-1-derived and primary human macrophages confirmed this selective chemokine response. While Csep1 P alone did not upregulate proinflammatory cytokines, THP-1-derived macrophages pre-incubated with Csep1 P produced a higher level of proinflammatory cytokines in response to commensal Escherichia coli , which was validated on primary human macrophages. Furthermore, silencing the delta like canonical notch ligand 4 ( DLL4 ) gene decreased the proinflammatory response of Csep1 P -mediated macrophages to E. coli . Collectively, our data demonstrate that the structurally unique Csep1 P reprograms macrophage response, which provides a mechanistic link between C. concisus infection and Crohn’s disease pathogenesis, and identifies Csep1 P as a potential target for therapeutic intervention.