In an in vitro profiling study of 37 UC patients and 4 healthy controls, systemic IgG was found to selectively target specific bacterial taxa, with active UC and elevated systemic inflammatory markers associated with increased IgG+ Probability Scores in oral-associated commensals (e.g., Granulicatella) and mucin-degrading taxa.
Systemic IgG responses in UC were selectively directed at specific bacterial taxa rather than uniformly at the whole gut microbiota.
Active UC and elevated systemic inflammatory markers were associated with increased IPS in oral-associated commensals, including Granulicatella.
Mucin-degrading taxa also showed increased IPS in active UC and with elevated systemic inflammatory markers.
Predictive functional profiling indicated predicted enrichment of pathways related to mucin degradation, capsular polysaccharide biosynthesis, and amino acid biosynthesis in IgG-targeted bacteria.
Exploratory Random Forest models using IPS features highlighted candidate taxa that differed by UC exacerbation, Clinical Activity Index, and C-reactive protein.
The study's limitations include a small sample, particularly only 4 healthy controls, in vitro design, and lack of independent validation of the models.
This study looked at whether antibodies (IgG) circulating in the blood of people with ulcerative colitis (UC) recognize particular bacteria in their own gut. The researchers mixed stool samples with each person's own blood serum in the lab and used DNA sequencing to identify which bacteria were bound by IgG. They created a score (the IgG+ Probability Score) to adjust for how common each bacterium was to begin with. They studied 37 people with UC and 4 healthy controls. The results suggest the immune system's IgG antibodies do not target all gut bacteria equally; they focus on certain groups. Higher IgG targeting of bacteria normally found in the mouth (such as Granulicatella) and of bacteria that break down the gut's protective mucus layer was linked to active disease and higher blood inflammation markers. Computer-predicted bacterial functions pointed to mucus breakdown, capsule-building, and amino acid production as features of these targeted bacteria. These findings are early. The study was small, included only four healthy controls, was done in laboratory conditions, relied on predicted rather than measured bacterial functions, and used machine-learning models that were not independently validated. This research suggests IgG-targeting profiles could help identify bacteria linked to UC activity, but it does not show these bacteria cause disease or that the approach is ready for clinical use.
Takahashi K, Nakayama-Imaohji H, Tada A, Emmanuel M, Mino Y, Ishikawa H, et al.. (2026). Profiling Systemic IgG-Targeted Gut Microbiota Reveals Disease Activity-Associated Bacterial Signatures in Ulcerative Colitis.. International journal of molecular sciences. https://doi.org/10.3390/ijms27209081