Severe COVID-19 patients present a concomitant significant increase in 1) IDO-1 activity, 2) increased production of KP metabolites, and 3) high levels of proinflammatory mediators including TNF-α and macrophage inflammatory protein-1 α (MIP-1α) both part of the cytokine storm [153, 154]. This evidence concerns the gene NPPA and COVID-19.