Which of the following is considered a first line of defense in innate immunity?

• A. Inflammation
• B. Natural killer cells
• C. Intact skin
• D. Fever

Answer: (C)

Verified step by step guidance

1. Understand the concept of innate immunity: Innate immunity is the body's first line of defense against pathogens. It is non-specific and includes physical, chemical, and cellular defenses that act immediately or within hours of an infection.
2. Identify the components of the first line of defense: The first line of defense includes physical barriers (e.g., intact skin and mucous membranes), chemical barriers (e.g., enzymes in saliva, stomach acid, and antimicrobial peptides), and mechanical processes (e.g., cilia movement and flushing actions like tears and urine).
3. Recognize the role of intact skin: Intact skin acts as a physical barrier preventing pathogens from entering the body. It is covered by keratinized cells and has antimicrobial properties due to secretions like sweat and sebum, which create an acidic environment hostile to microbes.
4. Differentiate between first and second lines of defense: Inflammation, fever, and natural killer cells are part of the second line of defense in innate immunity. These mechanisms are activated after pathogens bypass the first line of defense and enter the body.
5. Conclude that intact skin is the correct answer: Based on the definition and components of the first line of defense, intact skin is considered a primary physical barrier in innate immunity.