**Question:** Which of the following mediate Lewis triple response?

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

**Core Concept:** The Lewis triple response refers to the combined effects of three key mediators involved in allergic reactions: histamine, bradykinin, and leukotrienes. These mediators are released during an allergic response and contribute to the symptoms and signs observed in allergic reactions.

**Why the Correct Answer is Right:**

The correct answer, D. Leukotrienes, are a group of lipid mediators derived from arachidonic acid through the action of cysteinyl leukotriene synthetase. Leukotrienes are involved in various physiological processes, including inflammation, bronchoconstriction, and increased vascular permeability. In the context of the Lewis triple response, leukotrienes are crucial mediators of bronchoconstriction (Option D).

**Why Each Wrong Option is Incorrect:**

A. Histamine (Option A) is a well-known mediator of inflammation, vascular permeability, and bronchoconstriction. However, it does not solely mediate the triple response as it is only one of the mediators involved.

B. Bradykinin (Option B) contributes to vasodilation, increased vascular permeability, and bronchoconstriction, but it does not mediate the triple response since it is not the primary mediator responsible for all three responses.

C. Serotonin (Option C) is involved in various physiological processes, including bronchoconstriction, but it does not mediate the triple response as it is not the primary mediator responsible for all three responses.

**Clinical Pearl:** The Lewis triple response is a simplified model used to describe the combined effects of the three key mediators involved in allergic reactions. It highlights the importance of these mediators in understanding the pathophysiology of allergic reactions and their therapeutic implications.

**Correct Answer:** D. Leukotrienes mediate the bronchoconstriction component of the Lewis triple response, making it the correct answer. Understanding the role of these mediators in allergic reactions is essential for diagnosing, treating, and managing allergic disorders.