Which immune system cell or structure defends the body?

Cortisol is a steroid hormone produced by the adrenal glands that primarily helps regulate metabolism, immune response, and stress. While it plays a role in modulating inflammation and immune function, it does not directly defend the body against pathogens like antibodies do. Instead, cortisol can even suppress immune responses when present in high levels.

An allergen is a substance that triggers an allergic reaction in sensitive individuals, such as pollen or pet dander. Allergens themselves do not defend the body; rather, they can provoke an immune response that may include the production of antibodies. However, they are not part of the immune system's defense mechanisms.

Pathogens are harmful microorganisms, such as bacteria, viruses, and fungi, that invade the body and can cause disease. While pathogens are the targets of the immune system's defense, they do not provide defense themselves. The immune system must work to eliminate these invaders, with antibodies playing a critical role in this process.