Polymorphonuclear leukocytes (PMNs) Which statements accurately describe PMNs (e.g., neutrophils) in host defense?

Introduction / Context:Polymorphonuclear leukocytes (PMNs), primarily neutrophils in humans, are first responders in acute inflammation. Recognizing their origin, recruitment, and effector functions is fundamental to understanding innate immunity and clinical indicators like neutrophilia in infection.

Given Data / Assumptions:

• Complement activation generates chemoattractants (e.g., C5a).
• Hematopoiesis in bone marrow produces myeloid lineages, including neutrophils.
• Neutrophils perform phagocytosis and microbial killing.

Concept / Approach:

Complement fragments (C3a, C5a) and chemokines (e.g., IL-8/CXCL8) guide PMNs to infection sites. Neutrophils originate from hematopoietic stem cells via granulopoiesis and circulate briefly before migrating into tissues. Their antimicrobial arsenal includes reactive oxygen species (respiratory burst via NADPH oxidase), lysosomal enzymes, antimicrobial peptides, and formation of neutrophil extracellular traps (NETs). Defects (e.g., chronic granulomatous disease) illustrate their importance.

Step-by-Step Solution:

Verification / Alternative check:

Clinical labs show neutrophil recruitment to inflamed tissues; genetic or functional deficits in PMNs result in recurrent infections, validating their central role.

Why Other Options Are Wrong:

• “None of the above” contradicts well-established PMN biology.
• Choosing only one statement underestimates their multifaceted role.

Common Pitfalls:

• Confusing PMNs with mononuclear phagocytes (macrophages); both are phagocytic but differ in lifespan and roles.

Final Answer:

All of the above