LEP and obesity due to melanocortin 4 receptor deficiency: High level of IL-6 is also another key signature of severe SARS-CoV, MERS-CoV, and pandemic H1N1 influenza A viral infections (97–99) In individuals with obesity, adipocytes secrete pleiotropic leptin and pleiotropic adipocyte-specific IL-6 cytokine (91, 100).