The highly reactive chemotactic factors MCP-1 and MIP-1α made an aggregation of macrophagocyte in the vascular wall and mediated inflammatory response, then, induced the excitation of nuclear transcription factor c-Jun and then regulated the activation of activated protein 1 (AP-1), then activated MMP-9 promoter in its structural domain to raise MMP-9 mRNA expression, and finally induced the dissolution of extracellular matrix of vascular wall, causing the formation of intracranial aneurysm [21–23]. The gene discussed is MMP9; the disease is Dilatation of the cerebral artery.