Maternal gut bacteria promote neurodevelopmental abnormalities in mouse offspring

Maternal immune activation (MIA) contributes to behavioral abnormalities associated with neurodevelopmental disorders in both primate and rodent offspring(1-4). In humans, epidemiological studies suggest that exposure of fetuses to maternal inflammation increases the likelihood of developing Autism Spectrum Disorder (ASD)(5-7). We recently demonstrated that interleukin-17a (IL-17a) produced by Th17 cells, CD4(+) T helper effector cells involved in multiple inflammatory conditions, is required in pregnant mice to induce behavioral as well as cortical abnormalities in the offspring exposed to MIA(8). However, it is unclear if other maternal factors are required to promote MIA-associated phenotypes. Moreover, underlying mechanisms by which MIA leads to T cell activation with increased IL-17a in the maternal circulation are not well understood. Here, we show that MIA phenotypes in offspring require maternal intestinal bacteria that promote Th17 cell differentiation. Pregnant mice that had been colonized with the mouse commensal segmented filamentous bacteria (SFB) or human commensal bacteria that induce intestinal Th17 cells were more likely to produce offspring with MIA-associated abnormalities. We also show that small intestine dendritic cells (DCs) from pregnant, but not from non-pregnant, females upon exposure to MIA secrete IL-1β/IL-23/IL-6 and stimulate T cells to produce IL-17a. Overall, our data suggest that defined gut commensal bacteria with a propensity to induce Th17 cells may increase the risk for neurodevelopmental disorders in offspring of pregnant mothers undergoing immune system activation due to infections or autoinflammatory syndromes.