While IL-9 is an important promoter of mast cell expansion, IL-1β, IL-6, and TGF-β production, and Treg cell production and plays an important role in allergies, parasitic infections, and autoimmunity, it has not been specifically described in obesity and related diseases; therefore, in this case, the immune response could also be triggered and enhanced in the presence of LPS. The gene discussed is IL9; the disease is obesity due to melanocortin 4 receptor deficiency.