Figure 1: Association between prenatal infection and enhanced risk of neurodevelopmental disorders. During pregnancy, pathogens are thought to increase the risk of neurodevelopmental disorders in the offspring depending on the timing of infection and the magnitude of maternal immune response. Activation of the fetal immune system by de novo synthesis of cytokines sensitizes the brain to neurodevelopmental alterations. Interaction with other environmental and/or genetic factors also contributes to ASD etiology. Modeling prenatal immune activation represents a powerful tool to elucidate the relative contribution of these various factors for enhanced risk of ASD as well as other neurodevelopmental disorders.