IDO1 and COVID-19: They demonstrated that IFN-γ and its specific ISGs (chemokine C-X-C motif ligand 10 —CXCL10— and Indoleamine 2,3-Dioxygenase 1 —IDO1—) are more expressed in patients with mild COVID-19 presentation, but they tend to decrease in children with severe clinical manifestations, particularly in MIS-C [85].