Increased serum antibody response to commensal Lachnospiraceae flagellins appears to be preclinically associated with future risk for Crohn’s disease (CD) in healthy first-degree relatives (FDRs) of CD patients, a new study confirmed.
Pre-CD immunoglobulin G (IgG) seroreactivity toward a conserved bacterial flagellin epitope may be another early preclinical biomarker of CD, a study by Canadian, US, and Israeli researchers published in Clinical Gastroenterology and Hepatology confirmed. The findings add more evidence of early inflammatory markers long before CD diagnosis.
In addition to highlighting the interplay between gut microbes and the immune system, the presyptomatic rise in flagellin antibodies suggests this seroreaction may trigger disease onset rather than being a consequence of it. Whip-like proteins on the surface of bacteria, flagellins propel the bacteria around their environment in search of new habitats to colonize and new food sources, and they play a role in immune mediation.
“The impetus for the current study was the recognition that CD is preceded by a long, silent, preclinical phase during which immune dysregulation is already underway, but individuals remain asymptomatic,” co-senior author Sun-Ho Lee, MD, PhD, a clinician-scientist at the Lunenfeld-Tanenbaum Research Institute and the Centre for Inflammatory Bowel Disease at Mount Sinai Hospital in Toronto, told Medscape Medical News. “Although prior studies showed that antimicrobial antibodies can appear years before diagnosis, it was unclear which immune responses were most informative or biologically meaningful.”
To clarify that connection, the Mount Sinai team and colleagues examined data from the Crohn’s and Colitis Canada Genetic, Environmental, Microbial Project (GEM) involving more than 5000 healthy FDRs of CD patients in seven countries: Canada, the United States, the United Kingdom, Israel, Australia, New Zealand, and Sweden. So far, 130 FDRs have developed the condition during follow-up.
The group’s earlier published research had also suggested that elevated antimicrobial antibody responses are associated with CD risk, independent of usual biomarkers of abnormal gut barrier function, subclinical inflammation, and related genetic risks. This strengthened the idea that such responses are an early predisease event in CD.
Confirming their previous study, immune responses against bacterial flagellins — especially those of the anaerobic gut bacterium Roseburia hominis— were strongly associated with future CD risk in FDRs on average about 2.5 years before diagnosis.
On the clinical practice front, the flagellin protein’s strong immune-stimulating properties make it a promising contender as a vaccine adjuvant. “The flagellin epitope is an attractive candidate for a future preventive vaccine, but there are still plenty of unknown variables that need to be tested first,” study coauthor Williams Turpin, PhD, a translational research scientist and an assistant professor in the University of Toronto Temerty Faculty of Medicine’s Medical Department of Nutritional Sciences, told Medscape Medical News. “Previous work from Dr Benoit Chassaing from Institut Pasteur in Paris showed that a vaccine against Salmonella flagellin protects against colitis in mice, and a similar vaccine might work in humans.”
As to why certain individuals develop antibodies against this epitope before CD onset, Turpin said, “It could be a lack of immune tolerance, or that the flagellin peptide tends to translocate much more easily as a result of defects in barrier function. However, the presence of antiflagellin antibodies through vaccination prior to exposure to flagellins could perhaps be an efficient strategy to prevent the pathogenic effect of the specific epitopes identified here.”
Resources permitting, should all healthy FDRs of CD patients now be tested? “We previously showed that healthy FDRs have an up to 21% prevalence of abnormal response to flagellins, and there’s an even higher prevalence of up to 46% in those who later develop CD,” said coauthor Lee. “Testing for the presence of this epitope could identify individuals who are even higher risk. Those with the highest risk could then benefit the most from intervention aiming to reduce the risk of CD or delay its onset.”
First, however, there needs to be an understanding of the succession of events that lead to the increase in antibodies against this specific flagellin epitopes so that interventions can perhaps prevent pathogenesis, Lee cautioned. “We also don’t know the functional consequence of increased antiflagellin antibodies — whether this impacts the encroachment of specific species or increases the virulence potential of microbial species associated with CD,” he said.
Added co-senior author Ken Croitoru, MD, “With all the advanced biologic therapy we have today, patients’ responses are partial at best. We haven’t cured anybody yet, and we need to do better.”
Study Details
The current analysis monitored a nested case-control cohort of FDRs who later developed CD (n = 77). The median age of probands was 15 years (interquartile range, 12-21), 58.4 were female, and 80.5% were siblings rather than offspring, suggesting the influence of shared early-life environmental experience. The cohort consisted of 259 people from Canada, three from Israel, and eight from the United States.
CD patients were matched with healthy FDRs (n = 304) in a 1:4 ratio by age, sex, follow-up duration, and geographic location. Sera obtained at enrollment were probed for antimicrobial reactivity using a microbiota antigen microarray and a cytometric bead peptide assay. Conditional logistic regression was used to evaluate the association with CD onset, and a partial Spearman test was used to correlate serologic responses with variables such as lactulose-to-mannitol ratio (LMR), C-reactive protein, and fecal calprotectin (FCP). False-discovery rate was controlled using the Benjamini-Hochberg method (q < 0.05). “An ELISA [enzyme-linked immunosorbent assay] test could be used in future clinical settings given its low cost and rapid turnaround,” Lee said.
Of the 381 FDRs, 77 eventually developed CD over time. Of these, 28 had elevated antibody responses before diagnosis. Unsurprisingly, siblings showed especially strong responses.
Five antibodies positively correlated with FCP and three positively correlated with LMR. These IgG-seroreactive flagellins shared significant amino acid sequence homology, characterized by a conserved flexibility-linked hinge peptide within the D0-D1 domains of the amino terminus. A cytometric bead array confirmed the association of elevated IgG seroreactivity to the hinge peptide with future CD risk, independent of LMR and FCP.
Ashwin N. Ananthakrishnan, MBBS, MD, MPH, a clinician investigator at Mass General Research Institute and an associate professor at Harvard University in Boston who was not involved in the study, told Medscape Medical News, “This is an important study that builds on prior work from this group and others demonstrating that there exists a subclinical period in some patients who develop CD even many years before diagnosis.”
Ananthakrishnan cautioned, however, that the test is far from ready for prime time because while studies have established that informative at-risk markers exist, no interventions have yet been shown to prevent disease. “We still don’t know whether it’s limited, immunologically directed medical treatment, microbiome-based treatment, or lifestyle-based treatment such as diet that will be effective and acceptable to healthy patients who do not yet have a disease — not to mention the lack of data on the duration that such interventions would be necessary.”
Further validation and mechanistic studies are underway at Mount Sinai.
The research was funded by Crohn’s and Colitis Canada, the Canadian Institutes of Health Research, and the Leona M. and Harry B. Helmsley Charitable Trust. The cytometric bead array was developed with a grant from the Rainin Foundation.
Lee and Turpin had no conflicts of interest. Coauthor Elson reported a patent on Lachnospiraceae A4 Fla2, licensed by Prometheus Laboratories. He is founder, board member, and chief scientific officer of ImmPrev Bio, which is developing an antigen directed immunotherapy for CD. Elson and coauthors Zhao and Duck have filed a patent on the cytometric bead array.
Ananthakrishnan had no competing interests.
https://www.medscape.com/viewarticle/blood-test-widens-door-early-crohns-disease-diagnosis-and-2026a10006jq
