NO signaling might be central in understanding the disease, since the anatomic sites of COVID-19 symptoms, lung, heart, circulatory system and brain, also correlate with the expression patterns found for the three known human NO synthases: NOS1 (neural NOS; expressed in peripheral neurons), NOS2 (endothelial NOS; expressed in endothelial cells, cardiac myocytes, cardiac conduction tissue) and NOS3 (cytokine-inducible NOS; expressed in endothelial cells, myocytes, macrophages)53. Here, NOS2 is linked to COVID-19.