TYK2 and Alzheimer disease: Loss of function mutations of TYK2 are followed by impairment of the signaling pathways of IL-1, IL-12, and type 1 interferon, leading to dysregulation of differentiation of the Th1 lymphocyte, which is correlated with susceptibility to AD, skin infections, and high IgE serum levels, so that we know TYK2 plays an important role in Th2 lymphocyte differentiation.