Brain lesions caused by trauma, infection, or neurodegenerative disease result in the localised production of chemoattractants CCL21 and CX3CL1 by neurons and astrocytes, and MCP-1/CCL2 and SDF-1α/CXCL12 by activated microglia adjacent to the lesion [162]. This evidence concerns the gene CXCL12 and infection.