Question

Which of the following proteins or peptides blocks epithelial infection by bacteria, fungi and viruses ?

• A. Lysozyme
• B. Secretory leukocyte protease inhibitor
• C. Surfactant proteins SP - A
• D. Defensins (\(\alpha\) and \(\beta\))

Hint:

Remember that Defensins form 'pores' to 'deflate' pathogens.
\(\alpha\)-defensins are typically produced by neutrophils and Paneth cells (in the gut), while \(\beta\)-defensins are broadly secreted by diverse epithelial cells.

Answer 1

The Correct Option is D

Step 1: Concept:
The question asks us to identify the specific class of antimicrobial peptides that provide broad-spectrum barrier immunity on epithelial surfaces against a wide array of pathogens including bacteria, fungi, and viruses.

Step 2: Step-by-step Explanation:

• Epithelial surfaces (like the skin, respiratory tract, and gastrointestinal tract) serve as the body's first line of defense. They secrete various biochemical agents to neutralize invading pathogens.

• Lysozyme (Option A): Lysozyme is an enzyme found in tears, saliva, and mucus. Its primary function is to target and cleave the peptidoglycan linkages present specifically in bacterial cell walls, primarily acting against Gram-positive bacteria. It is not highly effective against fungi or viruses.

• Secretory leukocyte protease inhibitor (Option B): SLPI primarily protects local tissues from the detrimental effects of excessive proteolytic enzymes released during inflammation. While it has some antibacterial and antiviral properties, it is not the classic broad-spectrum blocker described.

• Surfactant proteins SP-A (Option C): SP-A is an opsonin found primarily in the alveoli of the lungs. It binds to pathogens to enhance their phagocytosis by alveolar macrophages. Its role is more about clearance than direct broad-spectrum killing.

• Defensins (\(\alpha\) and \(\beta\)) (Option D): Defensins are a major family of small, cysteine-rich, cationic antimicrobial peptides.

• Because they are cationic and amphipathic, they possess a strong affinity for the negatively charged lipid membranes characteristic of most bacteria, fungi, and enveloped viruses.

• Once attached, defensins embed themselves into the pathogen's lipid bilayer and form massive pores. This disrupts membrane integrity, leading to rapid leakage of essential cellular contents and subsequent pathogen death.

• Their broad-spectrum efficacy precisely fits the criteria of blocking infection by all three classes of pathogens mentioned.

Step 3: Final Answer:
Defensins are the correct multifaceted antimicrobial peptides.