Gut expression of CD71 and co-localisation with Dec-1 associated with high levels of serum SIgA and disease activity in SpA

Spondyloarthritis (SpA) correlates with elevated serum secretory-IgA (sSIgA). Retrotranscytosis, mediated by CD71 and Dectin-1, is linked to high sSIgA levels. This research investigated retrotranscytosis in the gut of SpA patients and its relationship with sSIgA, ileocolonoscopic findings, and activity indices. A cohort of 82 was derived from 180 patients based on selection criteria; 41 consented to DCE colonoscopy assessment. Measurements included CD71, Dec-1, sSIgA, and disease scores. Samples exhibiting apical CD71, Dec-1, or both were analysed for receptor/SIgA interactions. Apical CD71 and Dec-1 were predominantly found in the ileum. Multivariate analyses indicated CD71's association with heightened sSIgA (p = 0.05) and ASDAS-CRP (p = 0.036; OR 1.71; 95% CI 1.00-3.11), Dec-1's correlation with ileal inflammation (p = 0.05; OR 3.06; 95% CI 1.00-10.01), and the CD71/Dec-1 relationship with ileal villi atrophy (p = 0.038; OR 4.24; 95% CI 1.00-18.88). Microscopic evaluations demonstrated interactions between CD71/SIgA but not between CD71/Dec-1 or Dec/SIgA. The localised expression of CD71 and its co-localisation with Dec-1 may contribute to systemic increases in serum SIgA and activity scores in SpA patients. The findings suggest that sSIgA levels may serve as a non-invasive biomarker for gastrointestinal involvement in SpA and that retrotranscytosis could be a key mechanism in the gut-joint axis of SpA.