Objective: The diagnostic and prognostic properties of anti-integrin αvβ6 IgG autoantibodies in ulcerative colitis (UC) are poorly understood. We aimed to assess the diagnostic performance of anti-integrin αvβ6 autoantibodies and examine their association with disease outcomes.

Methods: Serum samples from a Swedish inception cohort of patients with suspected inflammatory bowel disease (IBD, n=473) were analysed using an in-house fluorescence enzyme immunoassay based on EliA™technology. Findings were validated in a Norwegian population-based inception cohort (n=570). Diagnostic performance was assessed by calculating the area under the curve (AUC) with 95% confidence intervals (CIs) and determining sensitivity and specificity. Reclassification was evaluated using the net reclassification index.

Results: In the discovery cohort, patients with UC, IBD-unclassified, or colonic Crohn's disease exhibited higher median autoantibody levels compared to symptomatic and healthy controls. In the validation cohort, the autoantibody demonstrated 79% sensitivity and 94% specificity for UC vs symptomatic controls at a cut-off of 400 UA/l. Its diagnostic performance (AUC=0.92, 95%CI 0.89-0.95) was superior to hs-CRP (AUC=0.65, 95%CI 0.60-0.70, P<0.001) and faecal calprotectin (fcalpro) (AUC=0.88, 95%CI 0.84-0.92, P=0.09). Combining the autoantibody with fcalpro further improved diagnostic accuracy (AUC=0.97, 95%CI 0.95-0.98) and patient reclassification (P<0.001). Autoantibody positivity was associated with a severe phenotype of UC, characterised by increased inflammatory activity and higher IL-17A and granzyme B levels. Higher autoantibody levels were linked to an aggressive disease course, remaining stable in aggressive UC but decreasing in indolent disease (P=0.003).

Conclusions: Anti-integrin αvβ6 is a reliable diagnostic and prognostic marker for UC, with potential clinical implementation.