Researchers with the UC Davis Center for Neuroscience and Department of Neurology have found that activating a mother’s immune system during her pregnancy disrupts the development of neural cells in the brain of her offspring and damages the cells' ability to transmit signals and communicate with one another. The finding suggests how maternal viral infection might increase the risk of having a child with autism spectrum disorder or schizophrenia.

“This is the first evidence that neurons in the developing brain of newborn offspring are altered by maternal immune activation,” McAllister, the study's lead author said. “Until now, very little has been known about how maternal immune activation leads to autism spectrum disorder and schizophrenia-like pathophysiology and behaviors in the offspring.”

The study was conducted in mice and rats and compared the brains of the offspring of rodents whose immune systems had been activated and those of animals whose immune systems had not been activated. The pups of animals that were exposed to viral infection had much higher brain levels of immune molecules known as the major histocompatibility complex I (MHCI) molecules.  This study provides the first evidence that MHCI levels are altered by the maternal immune system.

The researchers found that the high MHCI levels impaired the ability of the neurons from the newborn mice’s brains to form synapses, the tiny gaps separating brain cells through which signals are transmitted. Earlier research has suggested that ASD and schizophrenia may be caused by changes in the development of connections in the brain, especially the cerebral cortex.

The researchers experimentally reduced MHCI to normal levels in neurons from offspring following maternal immune activation.

“Remarkably, synapse density returned to normal levels in those neurons,” McAllister said. “These results indicate that maternal immune activation does indeed alter connectivity during prenatal development, causing a profound deficit in the ability of cortical neurons to form synapses that is caused by changes in levels of MHCI on the neurons."