IL6 and obesity due to melanocortin 4 receptor deficiency: IL6 is a potent cytokine that is expressed by different tissues under very different conditions, for example, exercise causes increased IL6 expression by muscle (Fischer, 2006), insulin signaling by hypothalamic neurons causes increased hepatic expression of IL6 (Könner et al., 2007), or obesity increases IL6 expression by adipose tissue (Mohamed-Ali et al., 1997).