IL33 and obesity due to melanocortin 4 receptor deficiency: Upon binding the membrane receptor ST2, IL-33 stimulates the expansion or activation of different kinds of type 2 immune cells including ILC2s, Tregs, and M2 macrophages to support type 2 responses characterized by type 2 cytokines like IL-4, IL-5, IL-10, and IL-13, thereby providing protection against obesity and insulin resistance [5, 7–12].