The aim of this study was to assess the effect that cystatin C exerts on cytokine production, NO and ROS production by human gingival fibroblasts incubated with P. gingivalis in order to be able to evaluate its potential therapeutic use against one of the main etiological agent causing periodontitis, as well as its potential impact on the severity of periodontal disease. The gene discussed is CST3; the disease is periodontal disorder.