Innate Immunity

1. What is the primary purpose of the immune system?

Answer: To destroy infectious agents while minimizing damage to the host.
Explanation: The immune response must eliminate pathogens without harming host tissues

2. Compare innate immunity and adaptive immunity in terms of specificity.

Answer:

• Innate immunity: nonspecific

• Adaptive immunity: specific

Explanation: Innate defenses respond the same way to many pathogens, while adaptive immunity targets specific antigens

3. How many lines of defense do humans have, and which are innate?

Answer: Three lines total; the first and second lines are innate.
Explanation: The third line is adaptive immunity

4. How does the skin act as a physical barrier to microbes?

Answer: Thick, multilayered epidermis with keratin that resists microbial penetration.
Explanation: Skin is tough, dry, and constantly shed, removing attached microbes

5. What are cell junctions and why are they important?

Answer: Protein complexes that prevent pathogens from passing between cells.
Explanation: Tight junctions block microbial entry into deeper tissues

6. What is mucus and how does it protect against infection?

Answer: A sticky secretion that traps microbes and debris.
Explanation: Mucus prevents pathogens from reaching epithelial cells

7. What is the mucociliary escalator?

Answer: Coordinated movement of cilia that pushes mucus away from the lungs.
Explanation: Removes trapped microbes from the respiratory tract

8. Define peristalsis and explain why diarrhea and vomiting can be protective.

Answer: Muscular contractions that move contents through the GI tract.
Explanation: They expel pathogens before infection can establish

9. Give two examples of mechanical defenses.

Answer: Urination and tears.
Explanation: Both physically flush microbes from the body

10. What role does the microbiome play in innate immunity?

Answer: Competes with pathogens for space and nutrients.
Explanation: Normal microbiota prevent pathogen colonization

11. What is sebum and how does it inhibit microbes?

Answer: Oil from sebaceous glands that creates an acidic environment.
Explanation: Low pH inhibits many pathogens

12. What antimicrobial substances are found in sweat?

Answer: Salt, lysozyme, and antimicrobial peptides.
Explanation: These inhibit and destroy microbes on skin

13. Where is lysozyme found and what does it do?

Answer: Tears, saliva, mucus, sweat, urine; breaks peptidoglycan.
Explanation: Lysozyme cleaves bonds in bacterial cell walls

14. Why is gastric juice an effective defense?

Answer: Extremely acidic (pH 1.2–3).
Explanation: Acid destroys many microbes and toxins

15. What are antimicrobial peptides (AMPs)?

Answer: Small proteins that damage microbial membranes or cell walls.
Explanation: Produced by skin, epithelial cells, and immune cells

16. What are acute-phase proteins and where are they produced?

Answer: Proteins produced by the liver during inflammation.
Explanation: They help inhibit microbial growth and enhance immunity

17. How do iron-binding proteins inhibit microbial growth?

Answer: They sequester iron needed for microbial metabolism.
Explanation: Starves microbes of essential nutrients

18. Where are complement proteins found?

Answer: Blood plasma, lymph, and tissue fluid.
Explanation: They circulate in inactive forms until activated

19. List the three outcomes of complement activation.

Answer:

1. Opsonization

2. Inflammation

3. Membrane attack complex (MAC)

Explanation: These enhance phagocytosis, recruit immune cells, and lyse microbes

20. What are leukocytes?

Answer: White blood cells involved in immunity.
Explanation: Derived from stem cells via hematopoiesis

21. What are the two major leukocyte categories?

Answer: Granulocytes and agranulocytes.
Explanation: Based on presence or absence of granules

22. Match the granulocyte with its function:

• Neutrophil: destroys extracellular bacteria

• Eosinophil: attacks parasitic worms

• Basophil: involved in allergic responses

Explanation: Each has specialized immune roles

23. What are neutrophil extracellular traps (NETs)?

Answer: DNA-protein webs that trap large pathogens.
Explanation: Used when pathogens are too large to phagocytose

24. What happens when monocytes leave the bloodstream?

Answer: They differentiate into macrophages or dendritic cells.
Explanation: Occurs when they enter tissues

25. What receptors do macrophages use to recognize pathogens?

Answer: Pattern recognition receptors (PRRs).
Explanation: PRRs bind pathogen-associated molecular patterns (PAMPs)

26. What role do dendritic cells play?

Answer: Activate the adaptive immune system.
Explanation: They link innate and adaptive immunity

27. How do NK cells recognize abnormal cells?

Answer: By absence or alteration of MHC-I.
Explanation: Healthy cells express MHC-I; infected cells may not

28. How do NK cells kill target cells?

Answer: Perforin forms pores; granzymes induce apoptosis.
Explanation: Leads to target cell death

29. What triggers an inflammatory response?

Answer: Breach of first-line defenses.
Explanation: Injury or infection initiates inflammation

30. What causes redness and heat during inflammation?

Answer: Vasodilation.
Explanation: Increased blood flow to injured area

31. What is diapedesis?

Answer: Movement of leukocytes out of blood vessels into tissues.
Explanation: Enabled by increased vascular permeability

32. List the five signs of inflammation.

Answer: Redness, heat, swelling, pain, loss of function.
Explanation: Classic indicators of inflammatory response

33. Why is fever considered a defense mechanism?

Answer: Inhibits pathogens and enhances immune activity.
Explanation: Fever increases immune cell function and limits microbial growth