A case of tubulointerstitial nephritis with infiltration of neutrophils and interleukin-17-positive cells associated with Behçet's disease.

Behçet's disease (BD) is a non-infectious inflammatory condition characterized by neutrophilic infiltration. In addition to primary symptoms, including oral and genital ulcers, ocular involvement, and skin lesions, BD can also affect various organs. However, renal involvement, particularly in tubulointerstitial nephritis, has rarely been described. Herein, a rare case of acute tubulointerstitial nephritis in a patient clinically diagnosed with BD is reported. The renal lesion presented with other symptoms of BD and fever, and was considered to be BD-related due to the presence of neutrophilic infiltration and its responsiveness to BD-directed therapy. Alterations in T-helper (Th) 1, Th2, and Th17 cytokine profiles are associated with BD activity. Interleukin (IL)-17 plays a central role in neutrophil activation, and recent studies have demonstrated a strong correlation between IL-17A levels and BD activity. In the present case, elevated serum IL-17A levels and infiltration of IL-17A-positive cells into the renal tissue reflected an active phase of BD and a BD-associated renal lesion.