To investigate whether IL-9 plays a role in the development of obesity and insulin resistance, we investigated the frequencies of IL-9 in several immune cell types, such as B cells, eosinophils, CD4 + T cells, macrophages and ILC2s, in the adipose tissue of normal control diet (NCD) and high-fat diet (HFD) mice after 12 weeks of diet. Here, CD4 is linked to obesity due to melanocortin 4 receptor deficiency.