**Question:** All of the following are mediators of inflammation except -

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

**Core Concept:** Inflammation is a complex physiological response to tissue injury or infection, characterized by the activation of immune cells and the release of various mediators that promote the inflammatory process. These mediators help to remove pathogens, eliminate damaged tissue, and initiate tissue repair. The four options provided are all known mediators of inflammation, except for one.

**Why the Correct Answer is Right:** Histamine is a small molecule released by mast cells and basophils during an immune response. It plays a crucial role in vasodilation, increased vascular permeability, and mucous gland secretion, leading to redness, warmth, and swelling, which are key features of inflammation. Histamine is part of the inflammatory response, making option D the correct answer to exclude.

**Why Each Wrong Option is Incorrect:**

**Option A (Prostaglandins):**
Prostaglandins are a class of lipid mediators derived from arachidonic acid, released by various cells during inflammation. They contribute to vasodilation, increased vascular permeability, and platelet aggregation, further enhancing the inflammatory process. This option is incorrect because prostaglandins are indeed mediators of inflammation.

**Option B (Leukotrienes):**
Leukotrienes are another lipid mediator family derived from arachidonic acid, released by activated leukocytes. They are involved in bronchoconstriction, increased vascular permeability, and mucus secretion, which are essential components of the inflammatory response. This option is incorrect since leukotrienes are also mediators of inflammation.

**Option C (Bradykinin):**
Bradykinin is a peptide mediator released during inflammation, resulting from the activation of the kallikrein-kinin system. It promotes vasodilation, increased vascular permeability, and platelet aggregation, contributing to the inflammatory response. This option is incorrect because bradykinin is indeed a mediator of inflammation.

**Core Concept:** Inflammation is a crucial aspect of the immune response, involving various mediators that promote vasodilation, increased vascular permeability, and cell recruitment to the site of injury or infection. These mediators include prostaglandins, leukotrienes, bradykinin, and histamine.

**Why Each Wrong Option is Incorrect:**

Option A (Prostaglandins) and Option B (Leukotrienes) are incorrect because they are involved in the inflammatory process and contribute to the symptoms associated with inflammation.

Option C (Bradykinin) is incorrect because it promotes vasodilation, increased vascular permeability, and cell recruitment, furthering the inflammatory response.

Option D (Histamine) is also incorrect as histamine is a key mediator of inflammation, causing vasodilation, increased vascular permeability, and vascular smooth muscle contraction.