AP-Micro Immunology and Host Defense 1 — Questions and Answers
Question 1: Which complement pathway is activated by mannose-binding lectin (MBL) recognizing carbohydrate patterns on microbial surfaces?
- Classical pathway
- Alternative pathway
- Lectin pathway (Correct answer)
- Terminal pathway
Correct answer: Lectin pathway
The lectin pathway is activated when MBL binds mannose residues on microbial surfaces, triggering MASP proteases.
Question 2: Which leukocyte is the predominant phagocyte recruited first during an acute bacterial infection?
- Macrophage
- Neutrophil (Correct answer)
- Natural killer cell
- Dendritic cell
Correct answer: Neutrophil
Neutrophils are the most abundant granulocytes and the first phagocytes to arrive at sites of acute bacterial infection.
Question 3: Which toll-like receptor (TLR) recognizes lipopolysaccharide (LPS) from gram-negative bacteria?
- TLR-2
- TLR-4 (Correct answer)
- TLR-5
- TLR-9
Correct answer: TLR-4
TLR-4, in complex with MD-2, recognizes LPS (endotoxin) and triggers innate immune signaling via MyD88.
Question 4: Natural killer (NK) cells preferentially kill target cells that:
- Overexpress MHC class I
- Overexpress MHC class II
- Lack or downregulate MHC class I (Correct answer)
- Express surface IgG
Correct answer: Lack or downregulate MHC class I
NK cells use 'missing self' recognition — they kill cells with absent or reduced MHC class I, which signals viral infection or malignancy.
Question 5: Which cytokine is the primary endogenous pyrogen responsible for inducing fever via the hypothalamus?
- IL-4
- IL-10
- IL-1β (Correct answer)
- IL-13
Correct answer: IL-1β
IL-1β (along with IL-6 and TNF-α) acts on the hypothalamus to raise the thermal set point, producing fever.
Question 6: Opsonization enhances phagocytosis by coating bacteria with which molecules recognized by phagocyte surface receptors?
- Antibiotics and lysozyme
- IgG antibodies and C3b complement fragments (Correct answer)
- Interferons and defensins
- Collectins and surfactant proteins only
Correct answer: IgG antibodies and C3b complement fragments
IgG (via Fc receptors) and C3b (via complement receptors) are the major opsonins that coat bacteria and enhance phagocyte binding and ingestion.
AP-Micro Immunology and Host Defense 1
Which complement pathway is activated by mannose-binding lectin (MBL) recognizing carbohydrate patterns on microbial surfaces?