Transgenic mice that overexpress CCL2 in the central nervous system (CNS) exhibit a robust accumulation of macrophages and activation of microglia in the brain [8,9], whereas mice deficient in the CCL2 gene show reduced leukocyte infiltration after autoimmune encephalomyelitis, traumatic brain injury, spinal cord injury and HIV-associated dementia [10-12]. Here, CCL2 is linked to dementia.