Question

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R
Assertion A: Endotoxaemia leads to acute and severe neutropenia
Reason R: Leukocyte migration and sequestration causes neutropenia
In light of the above statements, choose the correct answer from the options given below:

• A. Both A and R are true and R is the correct explanation of A
• B. Both A and R are true but R is NOT the correct explanation of A
• C. A is false but R is true
• D. A is true but R is false

Hint:

Acute endotoxemia causes a rapid shift of neutrophils from the circulating pool to the marginated pool (capillary walls, primarily in the lungs), resulting in sudden, severe circulating neutropenia.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Endotoxemia occurs when lipopolysaccharide (LPS), a component of the outer membrane of Gram-negative bacteria, enters the bloodstream.
LPS triggers a systemic inflammatory response, leading to rapid changes in circulating leukocyte profiles, particularly neutrophils.
Detailed Explanation:
Let us evaluate both statements:
- Assertion A: During the acute phase of endotoxemia (within minutes to hours of exposure), there is a rapid, dramatic decline in the number of circulating neutrophils, resulting in severe neutropenia. This is a classic finding in endotoxic shock. Thus, Assertion A is true.
- Reason R: When endotoxins enter the circulation, they stimulate endothelial cells and macrophages to release pro-inflammatory cytokines (such as TNF-\(\alpha\) and IL-1). These cytokines rapidly upregulate cell adhesion molecules (including selectins and integrins) on both endothelial cells and circulating neutrophils. Consequently, neutrophils marginate and adhere to the blood vessel walls, primarily within the pulmonary capillary bed. This sequestration, followed by active migration of leukocytes into surrounding tissues, depletes the circulating pool of neutrophils, resulting in circulating neutropenia. Thus, Reason R is true and directly explains the mechanism of Assertion A.

Step 2: Final Answer:
Both A and R are true, and R is the correct explanation of A.