Microglia and neuroinflammation: function, heterogeneity, and crosstalk

Microglia, the resident innate immune cells of the central nervous system (CNS), are indispensable for maintaining brain homeostasis, conducting immune surveillance, and responding to injury. Recent single-cell sequencing studies have revealed that activated microglia exhibit a spectrum of activation states that extend well beyond the classical proinflammatory/anti-inflammatory dichotomy, encompassing distinct subpopulations such as disease-associated microglia (DAMs), termed interferon-responsive microglia (IRMs), and lipid-droplet-accumulating microglia (LDAMs). Their remarkable plasticity enables microglia to adopt dual functional roles-either neuroprotective or neurotoxic-depending on the context of neuroinflammatory disease progression. Furthermore, microglia do not act in isolation but serve as central communicators within a dynamic cellular network of the CNS, interacting with neurons, astrocytes, oligodendrocytes, and peripheral immune cells to regulate processes such as synaptic pruning, inflammatory amplification, and myelin integrity and repair. This review provides a comprehensive overview of microglial origin, development, and classification, as well as the dynamic spectrum of microglial cellular states. Furthermore, we discuss the classical and latest mechanisms of microglia-mediated neuroinflammation and focus on the crosstalk between microglia and other cells of the CNS. The hub position of microglia within neuroinflammatory networks, together with their unique cellular characteristics, may unlock a promising frontier for the development of precision therapeutic strategies against neuroinflammatory disorders.