White matter injury and autistic-like behavior predominantly affecting male rat offspring exposed to group B streptococcal maternal inflammation.

The impact of the group B streptococcus (GBS)-induced maternal inflammation on offspring's brain has not yet been investigated despite GBS being one of the most frequent bacteria colonizing or infecting pregnant women. According to our hypothesis GBS-induced maternal immune activation plays a role in offspring perinatal brain damage and subsequent neurodisabilities such as autism. Using a new preclinical rat model of maternal inflammation triggered by inactivated GBS, we demonstrated placental, neuropathological and behavioral impacts on offspring. GBS-exposed placentas presented cystic lesions and polymorphonuclear infiltration located within the decidual/maternal side of the placenta, contrasting with macrophagic infiltration and necrotic areas located in the labyrinth/fetal compartment of the placenta after lipopolysaccharide-induced maternal inflammation. Brain damage featured lateral ventricles widening, predominately in the male, reduction of periventricular external capsules thickness, oligodendrocyte loss, and disorganization of frontoparietal subcortical tissue with no glial proliferation. Autistic hallmarks were found in offspring exposed to GBS, namely deficits in motor behavior, social and communicative impairments, i.e. profound defects in the integration and response to both acoustic and chemical signals that are predominant modes of communication in rats. Surprisingly, only male offspring were affected by these combined autistic-like traits. Our results show for the first time that materno-fetal inflammatory response to GBS plays a role in the induction of placental and cerebral insults, remarkably recapitulating cardinal features of human autism such as gender dichotomy and neurobehavioral traits. Unlike other models of prenatal inflammatory brain damage (induced by viral/toll-like receptor 3 (TLR3) or Gram-negative/TLR4), maternal inflammation resulting from GBS/TLR2 interactions induced a distinctive pattern of chorioamnionitis and cerebral injuries. These results also provide important evidence that beyond genetic influences, modifiable environmental factors play a role in both the occurrence of autism and its gender imbalance.