CD4 and obesity due to melanocortin 4 receptor deficiency: To further understand the mechanisms underlying the actions of GABA in regulating the HFD-induced obesity and insulin resistance, groups of C57BL/6 mice were fed with plain water or water containing GABA (2 mg/ml) for 4 weeks and their splenic CD4+Foxp3+ Tregs were characterized by flow cytometry analysis.