**Question:** Mediators of inflammation are all except -

A. Histamine
B. Prostaglandins
C. Bradykinin
D. Leukotrienes

**Core Concept:**
Mediators of inflammation are substances released by various cells, such as immune cells, endothelial cells, and mast cells, during the inflammatory process. These mediators are responsible for amplifying and prolonging the inflammatory response, leading to various clinical signs and symptoms. The primary roles of these mediators include vasodilation, increased vascular permeability, and recruitment of immune cells to the site of injury or infection.

**Why the Correct Answer is Right:**
The correct answer is **Histamine**. Histamine is a key mediator of inflammation, but it is not considered an "except" because it plays a significant role in the inflammatory response. Histamine is released by mast cells and basophils, which are part of the innate immune system. It is involved in vasodilation, increased vascular permeability, and recruitment of immune cells.

**Why Each Wrong Option is Incorrect:**

A. **Histamine:** As mentioned earlier, histamine plays a crucial role in the inflammatory process, making it an important mediator and not an "except" option.
B. **Prostaglandins:** Prostaglandins are lipid mediators derived from arachidonic acid, released by various cells during inflammation. They contribute to vasodilation, increased vascular permeability, and recruitment of immune cells. This option is incorrect as it is a mediator of inflammation, not an "except" option.
C. **Bradykinin:** Bradykinin is a potent vasodilator and increases vascular permeability. It is released during inflammation and acts as a mediator, not an "except" option.
D. **Leukotrienes:** Leukotrienes are lipid mediators involved in inflammation and are released from arachidonic acid via the action of 5-lipoxygenase. They contribute to vasodilation, increased vascular permeability, and recruitment of immune cells. This option is incorrect as it is a mediator of inflammation, not an "except" option.

**Clinical Pearl:**
Understanding the role of mediators of inflammation, such as histamine, prostaglandins, bradykinin, and leukotrienes, is essential for medical students and practitioners. Inflammation is a crucial part of the immune response, helping to protect the body from pathogens and promote tissue repair.

However, it is crucial to recognize that not all mediators are "except" options. Histamine, prostaglandins, bradykinin, and leukotrienes are all essential components of the inflammatory response, not exceptions. The correct answer, **Histamine**, is an important mediator of inflammation, released by mast cells and basophils during the immune response. Histamine contributes to vasodilation, increased vascular permeability, and recruitment of immune cells, which are all critical components of an effective immune response.