CD8A and obesity due to melanocortin 4 receptor deficiency: In contrast to Th1 and effector CD8+ T cells, Th2 cells, which produce type 2 cytokines such as IL-4 and IL-5, may protect against obesity and related insulin resistance; transfer of CD4+ T cells reverses weight gain and insulin resistance in HFD-fed lymphocyte-free mice, mainly through polarization into Th2 cells (32).