Final answer:
A) Histamine is the pre-packaged inflammatory mediator that activates the endothelium, released from mast cells, and contributes to the symptoms and processes of inflammation.
Step-by-step explanation:
The pre-packaged inflammatory mediator that helps activate the endothelium is histamine. Histamine is stored in and released from mast cells upon injury or in response to an allergen. This chemical signal provokes local vasodilation and increased permeability of the blood vessels, leading to swelling, redness, and the warmth associated with inflammation. Histamine also contributes to the process of chemotaxis, attracting white blood cells to the site of inflammation to further the immune response.
In contrast, prostaglandins are not pre-packaged but are synthesized in response to tissue injury and play a significant role in inflammation by causing vasodilation and pain. Interleukins are a type of cytokine involved in the communication between cells during the immune response. And while mast cells are involved in the release of histamine and other inflammatory mediators, they are not mediators themselves but rather cells that contain these mediators.