P. gingivalis results in the proteolytic destruction of transferrin through gingipain which is a cysteine protease and an important virulence factor for it; therefore, P. gingivalis can acquire iron which is necessary for its long-term growth.32 In addition, Campylobacter rectus and Prevotella intermedia use transferrin as a source of iron for their growth.33-34 Therefore, the mechanism above can explain the decrease in transferrin serum levels subsequent to chronic periodontitis and an increase in the counts of periodontopathogens. The gene discussed is CTSB; the disease is chronic periodontitis.