It was reported that renal involvement occurs in 21.7% (201/926) of AS patients.[11] The most commonly reported renal complications are IgA nephropathy,[12,13] followed by proliferative glomerulonephritis, secondary amyloidosis, and tubulointerstitial nephropathy.[14,15] Long-term use of NSAID is a common cause of tubulointerstitial nephropathy.[6] In AS patients, serum IgA is elevated,[16] and IgA and immune complexes are deposited in the mesangial area, where they induce mesangial cells to produce pro-inflammatory cytokines such as IL-6, IL-1, MIP, and TNFα. Here, TNF is linked to AA amyloidosis.