The study investigates the role of microglia in the fetal brain's response to maternal inflammation. Microglia, the resident phagocytes of the brain, are found to express receptors for pathogens and cytokines throughout embryonic development. Using a rodent model of maternal immune activation (MIA), the researchers demonstrate that MIA induces long-lasting transcriptional changes in fetal microglia that persist into postnatal life. These changes affect both neuronal and non-neuronal cells in the developing cortex. Importantly, these responses are abolished by selective genetic deletion of microglia, indicating that microglia are essential for mediating the effects of maternal inflammation on other cortical cell types. The findings highlight the critical and durable role of microglia in the fetal brain's response to maternal inflammation, suggesting them as a potential therapeutic target for preventing and treating adverse neuropsychiatric outcomes.The study investigates the role of microglia in the fetal brain's response to maternal inflammation. Microglia, the resident phagocytes of the brain, are found to express receptors for pathogens and cytokines throughout embryonic development. Using a rodent model of maternal immune activation (MIA), the researchers demonstrate that MIA induces long-lasting transcriptional changes in fetal microglia that persist into postnatal life. These changes affect both neuronal and non-neuronal cells in the developing cortex. Importantly, these responses are abolished by selective genetic deletion of microglia, indicating that microglia are essential for mediating the effects of maternal inflammation on other cortical cell types. The findings highlight the critical and durable role of microglia in the fetal brain's response to maternal inflammation, suggesting them as a potential therapeutic target for preventing and treating adverse neuropsychiatric outcomes.