p75NTR plays a critical role in the production of Aβ, neuronal death, neurite degeneration, and tau hyperphosphorylation; an increase in PKCδ expression is observed in human brains with AD, and the activation of PKCδ enhances toll-like receptor 4 (TLR4)-mediated pro-inflammatory signaling. Here, TLR4 is linked to Alzheimer disease.