**Core Concept**
Inflammation is a complex biological response to harmful stimuli, involving the activation of immune cells, blood vessels, and various chemical mediators. These mediators play crucial roles in initiating and sustaining the inflammatory response.

**Why the Correct Answer is Right**
The correct answer is a substance that is not typically associated with the mediation of inflammation. The other options are all well-known pro-inflammatory mediators. **Cytokines**, such as TNF-α (tumor necrosis factor-alpha), IL-1β (interleukin-1 beta), and IL-6 (interleukin-6), are key players in the inflammatory response. **Leukotrienes** are also pro-inflammatory mediators, involved in the recruitment of leukocytes to sites of inflammation. **Bradykinin** is a potent vasodilator and a mediator of pain, also involved in the inflammatory response.

**Why Each Wrong Option is Incorrect**
**Option A:** Cytokines are indeed mediators of inflammation, playing crucial roles in the initiation and maintenance of the inflammatory response.
**Option B:** Leukotrienes are also mediators of inflammation, involved in the recruitment of leukocytes and the induction of vascular permeability.
**Option C:** Bradykinin is a mediator of inflammation, involved in the induction of pain and vasodilation.

**Clinical Pearl / High-Yield Fact**
Remember that **histamine** is often considered a mediator of inflammation, but it is actually a key player in the allergic response, causing vasodilation, increased vascular permeability, and smooth muscle contraction.

**Correct Answer:** D.