On the contrary, C57BL/6J displayed higher levels of most of the tested circulating cytokines including IFN-γ, KC/GRO, IL-5, IL-10 and IL-6, which may explain the rapid increased leptin levels at 3d and concur for the higher susceptibility to obesity and insulin resistance in this strain31. This evidence concerns the gene LEP and obesity due to melanocortin 4 receptor deficiency.