It was also found that the ACE2/TMPRSS2 genes are (among others) downregulated by tumor necrosis factor (TNF) and are induced by several pro-inflammatory conditions including Barrett's esophagus, gastric infection by Helicobacter pylori, obesity, diabetes, autoimmune diseases, as well as by viral infections, cigarette smoking, growth factors, interferons (IFNs) and androgens [17]. Here, ACE2 is linked to obesity due to melanocortin 4 receptor deficiency.