CCL2 and Alzheimer disease: Our meta-analytic findings revealed that MCP-1 levels were significantly elevated in CSF, but not in blood, in subjects with AD and MCI, suggesting that increased MCP-1 level appears to be primarily from CNS-resident cells rather than from peripheral leucocytes, and that the CSF levels of MCP-1 had a larger effect size in AD-controls than in MCI-controls, indicating that increased CSF MCP-1 level is clearly associated with the severity of cognitive impairment.