MRGPRX2 and Alzheimer disease: In fact, in AD, the number of MCs, expression of SP, PAR2, and genes encoding MRGPRX2 were shown to be increased or upregulated; in particular, S. aureus-related MC degranulation via MRGPRX2 may be induced by δ-toxin or human β-defensin 2 from keratinocytes [71].