Many patients with Crohn’s disease (CD) have a heightened immune response to flagellins expressed by commensal gut bacteria Lachnospiraceae, with seroreactivity appearing up to 5 years prior to development of Crohn’s complications, according to investigators.
These findings suggest that lead author Qing Zhao, MD, PhD, of the University of Alabama at Birmingham, and colleagues reported.
Qing Zhao
Dr. Qing Zhao
Previously, Zhao and colleagues found that about 30% of patients with CD had elevated IgG responses to multiple Lachnospiraceae flagellins, and stronger reactivity was associated with higher flagellin-specific CD4+ T cells in circulation.
“In this study, we aimed to identify immunodominant B cell peptide epitopes shared among Lachnospiraceae bacterial flagellins in patients with CD and to correlate this immune reactivity with the clinical disease course,” the investigators wrote in Gastroenterology.
To this end, the investigators analyzed serum samples from adult CD patients, pediatric CD patients, and healthy infants without inflammatory bowel disease, with data derived from multiple sources. Adult patients with CD were part of a regional cohort recruited at the University of Alabama at Birmingham, while pediatric patients with CD came from the RISK Stratification Study, a multisite cohort study across the United States and Canada. Samples from healthy infants were collected from three diverse geographic locations: Uganda, Sweden, and the United States, providing a broad comparison of immune responses to Lachnospiraceae flagellin across populations.
Samples were analyzed via two main methods: a flagellin peptide microarray and a cytometric bead array. The microarray, comprising sequential Lachnospiraceae-derived peptides, enabled identification of IgG responses specific to individual bacterial peptides. The cytometric bead array allowed for multiplexed detection of IgG, IgA, and IgM antibodies to these peptides, quantifying immune reactivity and enabling correlation with clinical disease data.
This approach revealed that nearly half of patients with CD — both adults and children — had a strong IgG immune response targeting a specific bacterial peptide in the Lachnospiraceae flagellin hinge region. This response was linked to an increased risk of disease complications over time, suggesting the peptide’s potential as a biomarker for CD severity and progression, according to the investigators.
Of note, healthy infants also exhibited an elevated IgG response to the same bacterial peptide at around 1 year of age, but this response declined as they grew older, in contrast to its persistence in CD patients. This difference points to a possible failure in immune tolerance in CD, where the natural immune response to gut bacteria in infancy may become dysregulated, Zhao and colleagues explained.
“The flagellin cytometric bead array used in this study holds potential for a simplified yet robust diagnostic and prognostic assay for Crohn’s disease,” they concluded. “Given that reactivity to the dominant flagellin epitope is strongly associated with the development of disease complications, this technique may also assist in identifying patients with Crohn’s disease who would benefit from early therapy.”
Zhao and colleagues also called for future studies to characterize the role of flagellin hinge peptide–specific IgG antibodies in CD pathogenesis, and to explore the hinge peptide as a potential therapeutic target.The study was supported by a Synergy Award from the Kenneth Rainin Foundation, a Career Development Award from the Crohn’s and Colitis Foundation, and grants from the Department of Veterans Affairs, National Institute of Allergy and Infectious Diseases, National Institutes of Health, and National Institute of Diabetes and Digestive and Kidney Diseases. One coauthor and the University of Alabama at Birmingham hold a patent on Lachnospiraceae A4 Fla2, licensed for clinical application by Prometheus Laboratories. Four study coauthors have filed a patent for the flagellin peptide cytometric bead array. One coauthor serves as the founder and chief scientific officer of ImmPrev Bio, a company developing an antigen-directed immunotherapy for Crohn’s disease.
