ISG15 and COVID-19: These DE genes at D1 enriched for viral response pathways from the Reactome database, including “ISG15 antiviral mechanism”, “Interferon signaling”, “Interferon-γ signaling”, and “Interferon α/β signaling”, which were all upregulated at D1 in COVID-19 patients vs. non-COVID-19 sepsis patients (Figure 3B).