Anti-Integrin αvβ6 Autoantibodies as a Biomarker for Ulcerative Colitis in Patients With Axial Spondyloarthritis.

OBJECTIVE Anti-integrin αvβ6 autoantibodies (AIA) have recently been described as an informative biomarker for ulcerative colitis (UC), demonstrating a high sensitivity and specificity compared to patients without inflammatory bowel disease (IBD). Given the association between axial spondyloarthritis (AxSpA) and IBD, we sought to evaluate the potential of AIA as a biomarker in AxSpA patients with or without concurrent IBD. METHODS Using an established ELISA protocol, we measured AIA levels in sera of patients with (i) AxSpA and UC (n=18), (ii) AxSpA and Crohn's Disease (CD) (n=29), (iii) AxSpA alone (n=48), and healthy controls (HC) (n=48). AIA absorbance values were compared between patient groups and clinical variables were compared with AIA positivity. RESULTS Patients with AxSpA and UC showed a significant increase in mean absorbance and AIA positivity rate compared with AxSpA alone. For the diagnosis of UC among AxSpA patients, AIAs had a sensitivity of 55.6% and specificity of 89.6%, and receiver operating characteristic analysis yielded an area under curve value of 0.83. AIA positivity was associated with a family history of IBD in patients with AxSpA and UC. Surprisingly, AIA-positive patients had decreased mean CRP and BASDAI compared with AIA-negative patients. Examining serial samples, we observed that 3 of 10 AIA positive patients became AIA-negative, whereas AIA-negative to AIA-positive transitions were not observed. CONCLUSION AIA demonstrated potential as a diagnostic test for UC within AxSpA patients, particularly those with a family history of IBD. To our knowledge, this is the first study to date examining AIA in AxSpA.