Final answer:
An EpiPen's purpose is to treat severe allergic reactions, also known as anaphylaxis, by injecting a dose of epinephrine, which is critical for reversing the life-threatening symptoms.
Step-by-step explanation:
The purpose of an EpiPen® in the immune system is to treat allergic reactions. These devices are auto-injectable syringes preloaded with epinephrine, which is essential for treating life-threatening anaphylactic responses to allergens. Epinephrine works by constricting blood vessels to increase blood pressure, relaxing the smooth muscles in the lungs to ease breathing, modulating heart rate, and reducing swelling that might block the airways. Individuals with severe allergies carry EpiPens® in case of exposure to an allergen that could cause an anaphylactic response, which is an emergency situation where immediate treatment with epinephrine is necessary to prevent potential fatality.