Your immune system protects you from bacteria and viruses. Sometimes it misreads a harmless substance as a threat. When that happens, your body creates chemicals, like histamine, that trigger an allergic reaction. It's unclear what causes your immune system to make the mistake about certain things.
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Answer: Aorta
Explanation: The aorta is the largest artery in the body. It carries oxygenated blood from the left ventricle of the heart into systemic circulation. The aorta has many subdivisions that branch off into smaller arteries.
