Considering the host protective role of IL-9 during helminth infections and the proven ability of L. sigmodontis infection and filarial antigen (LsAg) administration to improve glucose and insulin tolerance by inducing a regulatory, type 2 phenotype [33], we proceeded to identify whether the LsAg-mediated protection observed in diet-induced obesity, as observed in our earlier studies, is dependent on IL-9. The gene discussed is IL9; the disease is obesity due to melanocortin 4 receptor deficiency.