In a murine model of AD, Staphylococcus aureus δ-toxin induces IL-4–dependent, MRGPRX2-mediated β-hexosaminidase release from MCs in an IgE-independent manner—an effect abrogated by the selective MRGPRX2 antagonist QWF (36). Here, MRGPRX2 is linked to Alzheimer disease.