It has been demonstrated that C5a can induce chemoattraction and induce secretion in mast cells during inflammation through a C5aR-mediated pathway (13); therefore, the aim of the present study was to determine whether a C5aR antagonist (C5aRA) inhibits AD in mice through suppressing the C5aR-mediated cascade action of mast cells. This evidence concerns the gene C5AR1 and Alzheimer disease.