IL-31 is also produced by Th1 cells, CD8+ T cells, monocytes/macrophages, dendritic cells, keratinocytes, eosinophils, basophils, mast cells, and fibroblasts, but Cevikbas et al. reported that Th2 cells are the major source of IL-31 in human AD [6,7]. This evidence concerns the gene IL31 and Alzheimer disease.