The spleen, once thought to be a fairly unimportant organ, has turned out to be a key relay passing information from the nerves to the immune system. Understanding this could eventually lead to treatments that use the spleen to send the right messages when the body is invaded.
Immune cells called macrophages produce tumour necrosis factor (TNF), an inflammatory messenger. Stimulating the vagus nerve, which runs from the brain to the chest and abdomen, reduces TNF production in the spleen.
Every year about 500,000 people develop severe sepsis (blood infection), which kills about 225,000 people in the United States.
For centuries the spleen was seen as a blood store, but in recent years it has been found to be a factory for immune cells and a meeting point between immune cells and nerves. It protects the body from infections, especially bacteria circulating in the blood.
The hope now is to adjust other immune functions, such as antibody production, through the spleen by stimulating the vagus nerve, as a way to change the course of infection and perhaps of some autoimmune diseases.
The nervous system is divided into sympathetic and parasympathetic parts, but the division isn't absolute: the vagus nerve is parasympathetic, yet it works through the splenic nerve to adjust immunity. Stimulating it lowers TNF production. So there are two separate routes by which the brain communicates with the spleen to regulate immunity, which may help treat infections.
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