Herein, we explored the effects of four cysteine protease inhibitors (Sialostatin L, Sialostatin L2, Iristatin, and Mialostatin) on mannan-induced psoriasis-like inflammation and evaluated the disease in terms of clinical and histological symptoms, infiltration of immune cells and expression of several pro-inflammatory cytokines. The gene discussed is CTSB; the disease is psoriasis.