Existing data indicate that the regulatory effect of NPY on the immune response can be either through the NPYR that directly acts on the surface of immune cells or indirectly through the regulation of physiological or pathological conditions such as BT, obesity, glucose metabolism, and mood (Figures 2, 3). In summary, NPY has a variety of regulatory effects on immune cell activity, including proliferation, differentiation, cytokine secretion, migration, and phagocytosis, some of which are even contradictory. This evidence concerns the gene NPY and obesity due to melanocortin 4 receptor deficiency.