A key feature of a severe allergic reaction known as anaphylaxis is a sudden drop in blood pressure and body temperature, which causes people to pass out and, if untreated, can die.
This reaction has long been attributed to the sudden dilation and leakage of blood vessels. But Duke Health researchers found that this response, particularly the drop in body temperature, requires another mechanism — the nervous system in a new study in mice.
The study, which appears online in the journal Science Immunology, could point to new targets for therapies to prevent or treat anaphylactic shock, which occurs in up to 5% of people in the U.S. each year in response to food allergies or insect or venomous animal bites.
“This finding identifies for the first time the nervous system as a key player in the anaphylactic reaction,” said lead author Soman Abraham, Ph.D., a professor in the Departments of Pathology, Immunology, and Molecular Genetics and Microbiology at Duke University School. medicine.
“Sensory nerves involved in thermal regulation — especially nerves that sense high environmental temperatures — send a false signal to the brain during anaphylaxis that the body is exposed to high temperatures, even though it is not,” Abraham said. “This causes a rapid drop in body temperature and blood pressure.”
Abraham and colleagues, including first author Chunjing “Evangeline” Bao, Ph.D. candidate in Abraham’s lab at Duke tracked the sequence of events when allergens activate mast cells—immune cells that trigger chemical reactions leading to swelling, difficulty breathing, itching, low blood pressure, and hypothermia.
The researchers discovered that one of the chemicals mast cells release when they are activated is an enzyme that interacts with sensory neurons, particularly those involved in the body’s thermoregulatory neural network.
When this neural network is stimulated as part of an allergic reaction, it is signaled to immediately shut down the body’s heat generators in brown adipose tissue, causing hypothermia. Activation of this network also causes a sudden drop in blood pressure.
The researchers confirmed their findings by showing that depriving the mice of a specific mast cell enzyme protected them from hypothermia, while directly activating heat-sensitive neurons in the mice produced anaphylactic reactions such as hypothermia and hypotension.
“By showing that the nervous system is a key player — not just immune cells — we now have potential targets for prevention or therapy,” Bao said. “This finding could be important for other conditions, including septic shock, and we are conducting these studies.”
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