The concept of maternal immune activation (MIA) originates from the epidemiology studies on the association of maternal infection with autism and schizophrenia1. Due to the absence of detectable replicating viral pathogens in the placenta or the fetal brain after maternal viral infection2,3, the effect of the infection on the offspring is hypothesized to be caused by the activation of the maternal immune system rather than the pathogens themselves.
To elucidate the cause-and-effect relationship between MIA and psychiatric disorders, injection of chemically synthesized, viral mimic double stranded RNA polyinosinic:polycytidylic acid (poly(I:C)) into pregnant rodents has been widely used as the animal model for MIA4,5. Poly(I:C) is recognized by toll-like receptor 3 (TLR3), and systemic administration of poly(I:C) induces viral-like acute inflammatory response. One of the mechanisms by which poly(I:C) produces behavioral abnormalities and neuropathologies in the offspring is by causing an imbalance of pro- and anti- inflammatory cytokines in the maternal-placental-fetal axis6. Several groups have adopted the MIA model to understand the etiology of psychiatric disorders7, and due to the diverse interests among research groups, various time points of immune activation have been used to achieve different perturbations on brain development and behaviors7.
The Paul H. Patterson laboratory at the California Institute of Technology adopts the strategy of injecting poly(I:C) into pregnant mice at embryonic 12.5 days (E12.5), which has successfully demonstrated that MIA is capable of inducing behavioral, neurological, and immunological changes in the offspring that are associated with autism and schizophrenia8-11. Our prior works show that MIA offspring display behavioral abnormalities (e.g., social impairment, communication deficit, repetitive behavior, anxiety-like behavior, and latent inhibition deficit8,10,12), immune dysregulation and cytokines imbalance8,13,14, alteration of fetal brain gene expression15, loss of Purkinje cell in lobule VII of cerebellum11, alteration of synaptic properties in hippocampus9, gene x environment interaction13, alteration of gut permeability, and gut microbiota composition16. Furthermore, therapeutic and prophylactic strategies are also developed from this model system13,16,17. By inducing MIA at E12.5, others have shown that MIA produces fetal microglial activation and cholinergic developmental alteration in basal forebrain18, strain specific interaction19, brain cerebral synaptosomal ultrastructural abnormalities, cerebral mitochondrial respiratory chain hyperfunction abnormalties, downregulation of cerebral synaptosomal molecules17, depressive-like behaviors, impairment in cognition and hippocampal long-term potentiation (LTP), and deficit of adult hippocampal neurogenesis20.
Here, we provide a detailed method of how to induce MIA at E12.5 by poly(I:C), as well as paradigms of how to apply this model to study the etiology of autism and schizophrenia. It is important to note that MIA is a risk factor for a variety of disorders4, and its outcomes are extremely sensitive to the time and method of induction as well as the husbandry of the pregnant dams. As such, even minor inconsistencies between laboratories often result in low reproducibility and/or different phenotypes in the offspring. Our method is specifically designed for those interested in studying MIA as an environmental risk factor for autism and schizophrenia, and the detailed description provided will help researchers improve the reproducibility of their data.