IL4 and Alzheimer disease: However, this signaling is quite different in PSO and AD [11]: the sensory neuron substance P (SP), interleukin (IL)-2, calcitonin gene-related peptide (CGRP), opioid receptors (OPR)M, and OPRK are involved in PSO-related itch, while thymic stromal lymphopoietin (TSLP), CGRP, IL-4, IL-13, and IL-31 are associated with AD pruritus.