Questions: Innate Immune System Components

Question 1

Which of the following best distinguishes innate immunity from adaptive immunity?

• A. Innate immunity requires prior exposure to a pathogen to be effective
• B. Innate immunity responds within minutes to hours using pre-formed pattern recognition, while adaptive immunity takes days and is antigen-specific
• C. Innate immunity produces antibodies that recognize specific pathogens
• D. Innate immunity is exclusively provided by T and B lymphocytes

Answer: (B)

Innate immunity is fast because it relies on germline-encoded pattern recognition receptors (PRRs) that detect conserved molecular patterns shared by broad classes of pathogens — no prior exposure needed. Adaptive immunity is slower (days) but generates antigen-specific responses and immunological memory. Options A, C, and D describe adaptive, not innate, immunity.

Question 2

Because the innate immune system responds so quickly, it can distinguish between hundreds of different specific pathogens and mount a tailored response to each one.

• T. True
• F. False

Answer: False

Speed is possible precisely because innate immunity is NON-specific. Pattern recognition receptors (PRRs) detect broad molecular patterns shared across many pathogens — called PAMPs (pathogen-associated molecular patterns) — not unique antigens. Antigen-specific tailoring is the job of the slower adaptive immune system. The trade-off is speed for specificity.

Question 3

A macrophage encounters a lipopolysaccharide (LPS) fragment from a bacterial cell wall. Describe the general sequence of events that follows and how this connects innate to adaptive immunity.

Model answer: The macrophage's Toll-like receptors (PRRs) detect LPS (a PAMP), triggering phagocytosis and pro-inflammatory signaling. The macrophage releases cytokines (e.g., IL-1, TNF-α) that recruit neutrophils and amplify local inflammation. As an antigen-presenting cell, it processes bacterial peptides and displays them on MHC class II molecules, activating CD4+ T cells and bridging innate and adaptive immunity.

This question tests the integrative role of the innate response. The macrophage is both an immediate effector (phagocytosis, cytokine release) and a bridge to adaptive immunity (antigen presentation). Understanding this dual role is central to immunology — innate immunity does not just fight the infection independently but also instructs the adaptive response.