**Question:** Acute phase reaction in acute inflammation are

A. Increased vascular permeability
B. Vasodilation
C. Decreased vascular permeability
D. Altered leukocyte function

**Core Concept:** Acute phase reactions are a part of the host defense mechanism in response to tissue injury or infection, characterised by various physiological changes that help in reducing tissue damage, removing the causative agent, and promoting tissue repair.

**Why the Correct Answer is Right:** Acute phase reactions involve a cascade of events, including increased vascular permeability (option A), which allows inflammatory cells and plasma proteins to enter the injured or infected tissue, enhancing the immune response and phagocytosis, respectively.

**Why Each Wrong Option is Incorrect:**

B. Vasodilation (option B) is not correct, as vasodilation would increase blood flow to the affected area, potentially worsening tissue damage and making the situation worse.

C. Decreased vascular permeability (option C) is incorrect as it goes against the purpose of acute phase reactions, which aim to increase vascular permeability to enhance the immune response.

D. Altered leukocyte function (option D) is not the primary focus of acute phase reactions; instead, increased vascular permeability is the primary response to allow immune cells and proteins to reach the site of infection or injury.

**Clinical Pearl:** Understanding acute phase reactions is crucial in understanding inflammation, as it helps in interpreting clinical scenarios like fever, altered liver function tests, and increased C-reactive protein (CRP) levels in various diseases.

**Correct Answer:** Acute phase reactions primarily focus on increased vascular permeability (option A) to enhance the immune response and promote tissue repair in acute inflammation.