No difference in serum levels of B‐cell activating receptor and antibodies against cytolethal distending toxin B and flagellin in post‐infectious irritable bowel syndrome and chronic fatigue syndrome after Giardia infection

Background and Aim Functional gastrointestinal disorders (FGIDs) and chronic fatigue syndrome (CFS) frequently occur as comorbid conditions to each other. A shared etiology of these syndromes has been proposed because of their shared symptomatology and triggering by infections. Antibodies against the bacterial antigens cytolethal distending toxin B (CdtB) and flagellin have been proposed to be biomarkers of irritable bowel syndrome (IBS), especially diarrhea‐predominant IBS (IBS‐D). It is unknown if they may also be associated with comorbid conditions such as CFS. On the other hand, elevated level of B‐cell activating factor (BAFF) has been associated with CFS and inflammatory bowel disease (IBD) and subjective food intolerance. Methods We evaluated serum levels of anti‐flagellin and anti‐CdtB using an in‐house enzyme‐linked immunosorbent assay (ELISA) and BAFF with a commercially available ELISA kit in a cohort of patients who developed fatigue syndromes and/or FGIDs after Giardia infection, by comparing them with healthy controls without these conditions. Results We did not find significant differences in circulating BAFF, anti‐CdtB, or anti‐flagellin antibody levels in these patient groups compared to healthy controls. Therefore, our results do not support a role for BAFF, anti‐CdtB, or anti‐flagellin antibodies as universal biomarkers for IBS or CFS. Conclusion BAFF, anti‐CdtB, or anti‐flagellin antibodies cannot be considered as universal biomarkers for IBS or CFS.