APRIL/BAFF upregulation is associated with clonal B‐cell expansion in Hunner‐type interstitial cystitis

Hunner-type interstitial cystitis (HIC) is a chronic inflammatory disease of the urinary bladder with an unknown etiology. We conducted comprehensive immunogenomic profiling of bladder specimens obtained by biopsy and cystectomy from 37 patients with HIC. Next-generation RNA sequencing demonstrated abundant plasma cell infiltration with frequent light chain restriction in HIC-affected bladder tissue. Subsequent analysis of the B-cell receptor repertoire revealed spatial and temporal expansion of B-cell clones. The extent of B-cell clonal expansion was significantly correlated with the gene expression levels of TNFSF13 and TNFSF13B, which encode APRIL and BAFF, respectively. These findings indicate that APRIL and BAFF are the key regulators of clonal B-cell expansion in HIC and might serve as therapeutic targets in this debilitating disease.