Background and aims We report the case of a 62-year-old woman. Psoriasis Vulgaris (Psoriasis) was diagnosed in X-31 year and also SLE with nephritis (WHO IIIA) in X-11. She was treated with high-dose methylprednisolone and cyclosporine A (CsA) to achieve remission. Methylprednisolone was reduced to 4 mg/day.

Methods Because of renal dysfunction, although CsA was discontinued in May X, psoriasis, renal dysfunction and proteinuria became further worse, she was admitted to hospital in July X. She was diagnosed with SLE flare with class IV-G(A/C)+V lupus nephritis (INS/RPS) and associated psoriasis. The SLEDAI score was 16 and psoriasis area and severity index (PASI) score was 16. Although high-dose corticosteroid (1 mg/kg/day) and a concomitant first dose of IV cyclophosphamide (IVCY) were started, anasarca was still observed and S-Cr was increased from 1.98 to 2.85 mg/dL. Because proportion of activated Th17 cells were increased in peripheral blood(PD), and the infiltration of many lymphocytes and IL-17-positive cells in renal interstitium, secukinumab, an antibody against IL-17A, was administered.

Results Then, anasarca and nephrosis was improved and S-Cr was decreased to 1.20 mg/dL in proportion to the reduction in activated Th17 cells in PD.

Conclusions Although recent studies have begun to shed light on the role of IL-17 in the pathogenesis of SLE, there is no convincing evidence in actual patients. In this case, improvement of disease activity of SLE was correlated with the decrease of activated Th17. This is the first report that the IL-17-targeted therapy for SLE was shown to be effective in a patient skewing towards Th17-phenotype.