In diet-induced obesity (DIO) mice with influenza A infection, impaired host defence was associated with a decrease in type I interferon (IFN-α and IFN-β), a delay in IL-6 and TNF-α expression, that increased to higher concentrations than those in lean animals, and impaired the cytotoxicity of natural killer cells(90). Here, TNF is linked to obesity due to melanocortin 4 receptor deficiency.