However, the absence of increases in serum IL-17A (Figure 4A) despite increases in AHR (Figure 3) with HFD, in conjunction with the observations that obesity-related AHR does not occur in IL-17A-deficient mice (15), suggest that the source of the IL-17A that is important for AHR is the lung not the blood. Here, AHR is linked to obesity due to melanocortin 4 receptor deficiency.