CXCL12 and Alzheimer disease: The following problems remain to be solved: (1) the specific role of CXCR4 in the development of AD remains unclear; (2) How the CXCL12/CXCR4 axis regulates downstream molecules to affect AD needs to be further determined; and (3) how the CXCL12/CXCR4 axis interacts with other pathways to affect the occurrence and development of AD has not been clarified.