A new study led by researchers at Osaka University has added an surprising information about neuron development presenting that immune cells may play a key role in helping myelin to form around the newly minted neuron. This study was published in Nature Neuroscience.
Neurons are basic unit of the nervous system which are the specialized cells that communicate using electrical signals. Every neuron is made of a cell body (also called a soma), dendrites and an axon. The signal transmit down through long, wire-like projections called axons. The transmission of these signals requires myelin which is a fatty substance that surrounds axons in much the same way that plastic coating surrounds an electrical wire. There are numerous neurological disorders, including autism and schizophrenia, are believed to be driven in part by the failure of myelin to properly surround axons during development.
Our immune system is essential for our survival. The most important part of the immune system are the T and B cells which are vital players in the immune system; These cells circulate through the body to find antigens and after recognition, mount a protective response. It is assumed that these cells are blocked from accessing the brain though they spend most of their time passing through the bloodstream and the lymph nodes
“The central nervous system is protected from pathogens by a highly selective barrier that keeps the circulatory system physically separated from the brain,” lead author Shogo Tanabe explains. “It’s generally believed that this barrier also excludes immune cells from the brain. Our study suggests otherwise, though, as we found that a certain type of B cell is quite abundant in the ventricles, meninges, and choroid plexus in the brains of young mice. Even more surprising, these cells appear to stimulate axon myelination in the surrounding neurons.”
Neurons can not produce myelin by their own hence supportive cells called oligodendrocytes makes the myelin sheath that wraps around axons. During their research, scientists discovered that the B immune cells, called B-1a cells, ensure that enough of these oligodendrocytes are available in the developing brain to support adequate myelination.
“We experimentally depleted B cells from the brains of young mice and saw oligodendrocyte numbers drop significantly, ” Tanabe adds. “It turns out that so-called natural antibodies secreted by B-1a cells induce oligodendrocyte precursors to proliferate. These antibodies are typically involved in immune surveillance, but in this case, they promote the myelination of axons.”
Current studies have shown that T cells can occupy the meninges and play a role in learning and memory. However, this is the first study implicating B cells in myelin production during early development. The study may have broad implications for diseases driven by early defects in neuronal growth.
“Prior work has indirectly hinted at a role for B cells in neurodevelopmental disorders,” lead investigator Toshihide Yamashita notes. “Our findings provide direct evidence that B cells reside in the mouse neonatal brain and promote both oligodendrocyte proliferation and neuron myelination. This suggests to us that B cell dysfunction in early development may contribute to later mental disorders, a possibility that we believe deserves further exploration in future studies.”