These immune mediators, such as transforming growth factor-β1 (TGF-β1), IL-5, a proliferation-inducing ligand (APRIL), also known as tumor necrosis factor ligand superfamily member 13 (TNFSF13), and retinoic acid (RA), are linked to IgA production, so the reduction of myeloid immune compartments within the lamina propria and lymph nodes contributes to reduced IgA in obesity. The gene discussed is TNFSF13; the disease is obesity due to melanocortin 4 receptor deficiency.