ACE2 receptors appear crucial for SARS-CoV-2 attachment, suggesting the need to define SARS-CoV-2 adhesion susceptible cell, which is a cell bearing an adhesion disposition realized in a SARS-CoV-2 attachment stage, where the functional receptor material base ACE2 is imported to IDO-COVID-19 from the Protein Ontology [65] (from which it also imports recently created terms for SARS-CoV-2 proteins). This evidence concerns the gene IDO1 and COVID-19.