MTOR and obesity due to melanocortin 4 receptor deficiency: Taken together, our results demonstrate that obesity-associated elevation of leptin may result in activation of the mTOR/MEK (upstream of MAPK)-IRE1-XBP1 axis in pro-allergic lymphocytes that promote cell survival and cytokine production, therefore exacerbating allergic airway disease (outlined in Fig. 7D).