IL4 and obesity due to melanocortin 4 receptor deficiency: Interleukin (IL)-4 plays a role in the energy metabolism and pathogenesis of obesity [21] and has been shown to increase hepatic TG content by facilitating free fatty acid uptake and expression/activity of lipogenic enzymes in experimental models [21] (Figure 1 shows the effect of leptin and IL-4 on hepatic lipid metabolism).