IL31 and Alzheimer disease: In AD, epithelial cell–derived cytokines such as IL-25, IL-33, and TSLP promote the overexpression of Th2 cytokines, including IL-4, IL-5, IL-13, and IL-31, either directly through Th2 cytokine-secreting cells or indirectly through dendritic cell-mediated polarization (38).