Human microbiota flagellins drive adaptive immune responses in Crohn's disease.

Abstract: Background and Aims Crohn's Disease (CD) and ulcerative colitis (UC) are characterized by dysregulated adaptive immune responses to the microbiota in genetically susceptible individuals, but the specificity of these responses remains largely undefined. Therefore, we developed a microbiota antigen microarray to characterize microbial antibody reactivity, particularly to human-derived microbiota flagellins, in inflammatory bowel disease. Methods Sera from healthy volunteers at the University of Alabama at Birmingham (UAB), n=87; patients recruited from the Kirklin Clinic of UAB Hospital, including patients with Crohn's disease, n=152; and Ulcerative colitis, n=170; was individually probed against microbiota bacterial flagellins of both mouse and human origin and analyzed for IgG and IgA antibody responses. Circulating flagellin-reactive T effector (TE, CD4+CD154+) and T regulatory (TREG, CD4+CD137+) cells were isolated and evaluated in selected patients. Resulting adaptive immune responses were compared with corresponding clinical data to determine relevancy to disease behavior. Results We show that IBD patients express selective patterns of antibody reactivity to microbiota flagellins. CD patients, but not UC patients, display augmented serum IgG to human ileal-localized Lachnospiraceae flagellins, with a subset of patients having high responses to >10 flagellins. Elevated responses to CBir1, a mouse Lachnospiraceae flagellin used clinically to diagnose CD, correlated with multi-Lachnospiraceae flagellin reactivity. In this subset of CD patients, multi-flagellin reactivity was associated with elevated flagellin-specific CD154+CD45RA- T memory cells, a reduced ratio of flagellin-reactive CD4+ TREG to TE cells, and a high frequency of disease complications. Conclusions CD patients display strong adaptive immune response to human-derived Lachnospiraceae flagellins, which may be targeted for prognosis and future personalized therapies.