Microglia are the resident immune cells of the central nervous system and are crucial for brain development, maintenance and response to injury. They populate the brain early in embryonic life, originating from yolk sac progenitors that migrate into the developing neural tissue, where they proliferate and establish long lasting populations.

In the healthy brain, microglia continuously survey their surroundings with highly motile processes. They help shape neural circuits by pruning synapses, clearing apoptotic cells and regulating neurogenesis. Their activity is tightly controlled by neuronal and glial signals that keep them in a homeostatic, neuroprotective state.

When microglia sense pathogens, damaged cells or protein aggregates, they rapidly change morphology, gene expression and behavior. They can adopt diverse reactive phenotypes that range from protective, promoting debris clearance and tissue repair, to harmful, driving inflammation and neurotoxicity. This functional spectrum is regulated by complex signaling networks, including cytokines, chemokines and metabolic pathways.

Microglial dysfunction is now recognized as a key contributor to many neurological and psychiatric conditions. In neurodegenerative diseases such as Alzheimer’s and Parkinson’s, microglia interact with misfolded proteins, can fail to clear aggregates efficiently and may sustain chronic inflammation that worsens neuronal loss. Genetic studies have identified risk variants in microglia related genes, highlighting their central role in disease susceptibility.

Contemporary research focuses on understanding microglial heterogeneity across brain regions, ages and disease states using single cell technologies and in vivo imaging. There is growing interest in therapeutically targeting microglia to modulate their responses, enhance beneficial functions and limit detrimental inflammation in a range of brain disorders.