In summary, it is quite possible that the high circulating levels of IL-6 observed in obesity generate, in turn, the down-modulation of the signalling pathway of IL-6 and ultimately a deficit of its signal, producing an IL-6-deficient like situation reminiscent of that found in obese IL-6-/- mice and obese Zucker rat models. Here, IL6 is linked to obesity due to melanocortin 4 receptor deficiency.