Our data show that the expression levels of IL-6, IL-1β, IL-10, CRP, IDO1 and ACE2 were significantly higher in subjects classified as having severe illness than in those with mild or moderate illness and that patients with mild/moderate illness had significantly higher expression levels of IL-6, IL-1β, IL-10, CRP and ACE2 than COVID-19-free (control) subjects. The gene discussed is IDO1; the disease is COVID-19.