What is considered the "front line" of immune system defense?

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Quizplus · Accepted Answer

Leukocytes, also known as white blood cells, are considered the "front line" of immune system defense. They are responsible for identifying and attacking foreign substances in the body, such as viruses and bacteria. Antigens are foreign substances that trigger an immune response, but they are not a part of the immune system itself. Cortisol is a hormone produced by the adrenal gland that helps regulate the immune response, but it is not a part of the immune system either. The hypothalamus is a region of the brain that helps regulate many bodily functions, including the immune system, but it is not considered the "front line" of immune system defense.

What Is Considered the "Front Line" of Immune System Defense