Although IL-33 is strongly implicated in inducing eosinophilic inflammation in anti-parasite or allergic type 2 immune responses (21, 30), the cytokine has also shown protective effects in models of colitis (31), graft-vs.-host disease (32), autoimmunity (33), obesity (34), wound healing and tissue restoration (35, 36). Here, IL33 is linked to obesity due to melanocortin 4 receptor deficiency.