Reactive vs Senescent Astrocyte activity. Pro-inflammatory mediators (IL-1a, TNF-a, and C1q or LPS) released by activated microglia generate reactive astrocytes. Reactive astrocytes express C3 and secrete pro-inflammatory cytokines (TNF-a, IL-1b, and IL-6), while senescent astrocytes secrete the SASP (IP-10, IL-1a, GM-CSF, and MCP-1), activating microglia, both of which are related to the progression of neurodegenerative diseases.