Next, to elucidate if suppression of IFN responses in obesity is functionally related to increased airway leptin concentrations, we used pulmonary recombinant leptin protein administration (at a previously reported dose26) in mice (Fig. 5a) to mimic the increased airway concentrations observed in human subjects and permit study of direct causal effects upon antiviral immunity. This evidence concerns the gene LEP and obesity due to melanocortin 4 receptor deficiency.