To better investigate the role of circulating monocytes in COVID-19, we performed Ingenuity Pathway Analysis (IPA) [QUIAGEN lnc., https://digitalinsights.qiagen.com/IPA, (57)], and found that, compared to healthy donors, the most significantly downregulated pathways in all the pathological conditions were the Oxidative Phosphorylation signaling, Tumor Microenvironment signaling categories and Translation Initiation Factor 2 (eIF2) signaling, while PD-1, PD-L1 Cancer Immunotherapy Pathway was downregulated in the severe pathological group (Figure S7). The gene discussed is CD274; the disease is COVID-19.