ACE2, Furin, and TMPRSS are expressed in periodontal tissues. SARS-CoV-2 is detected in the periodontal tissues of COVID-19 patients. Periodontal tissues are infected with SARS-CoV-2, so they would supply SARS-CoV-2 to gingival crevicular fluid. The gene discussed is ACE2; the disease is COVID-19.