P2RX7 and obesity due to melanocortin 4 receptor deficiency: Furthermore, studies using a P2X7 knockout mouse also demonstrated that the lack of P2X7 produces the expansion of T follicular helper cells (Tfh) in the Peyer’s patches (PPs) of the small intestine, which leads to increased production of secretory immunoglobulin A (SIgA) and to the abundance of commensals that affect the host’s metabolism, resulting in an obesity phenotype and an alteration of glucose homeostasis [100,101].