Innate immune signaling and functions in astrocytes.

Astrocytes, long considered supportive cells of the central nervous system (CNS), have critical roles in innate immunity. This Review explores immune signaling pathways in astrocytes, including pattern recognition through Toll-like receptors, nucleic acid sensors and inflammasomes. These pathways enable the detection of danger signals and initiate protective responses and endogenous innate immune functions. Downstream signaling pathways, including the interferon, NF-κB and STAT3 pathways, mediate astrocyte reactivity and drive cytokine secretion, antiviral responses, phagocytosis and many other immune functions. While these responses are crucial for CNS health, their dysregulation can contribute to chronic inflammation and neurodegeneration in conditions such as Alzheimer's disease, Parkinson's disease, multiple sclerosis and amyotrophic lateral sclerosis. Additionally, astrocytes exhibit regional heterogeneity in their immune behaviors, which may influence disease trajectories. We highlight unresolved questions regarding the immune functions of astrocytes, their interplay with professional immune cells and their dual protective and pathological roles.