ABD Basic Science and Immunology 3 — Questions and Answers
Question 1: Melanin is synthesized from which amino acid precursor via the enzyme tyrosinase?
- Tyrosine (Correct answer)
- Tryptophan
- Phenylalanine
- Histidine
Correct answer: Tyrosine
Tyrosinase converts tyrosine to DOPA and then dopaquinone in melanogenesis.
Question 2: Which cell adhesion structure connects adjacent keratinocytes and is targeted by autoantibodies in pemphigus vulgaris?
- Desmosome (Correct answer)
- Hemidesmosome
- Tight junction
- Gap junction
Correct answer: Desmosome
Desmosomes (via desmoglein 3) are disrupted in pemphigus vulgaris causing acantholysis.
Question 3: Type VII collagen, defective in dystrophic epidermolysis bullosa, forms which structure?
- Anchoring fibrils (Correct answer)
- Anchoring filaments
- Keratin intermediate filaments
- Elastic fibers
Correct answer: Anchoring fibrils
Type VII collagen forms anchoring fibrils that attach the lamina densa to dermis.
Question 4: The complement pathway activated directly by antigen-antibody complexes begins with which component?
- C1 (Correct answer)
- C3
- Factor B
- Mannose-binding lectin
Correct answer: C1
The classical pathway is initiated by C1 binding to antibody-antigen complexes.
Question 5: Which vitamin is synthesized in the skin from 7-dehydrocholesterol upon UVB exposure?
- Vitamin D (Correct answer)
- Vitamin A
- Vitamin K
- Vitamin C
Correct answer: Vitamin D
UVB converts 7-dehydrocholesterol to previtamin D3 in the epidermis.
Question 6: Mast cell degranulation in urticaria releases which principal preformed mediator responsible for the wheal?
- Histamine (Correct answer)
- Prostaglandin E2
- Leukotriene B4
- Bradykinin
Correct answer: Histamine
Histamine is the key preformed mediator stored in mast cell granules driving urticaria.
Question 7: The stratum corneum barrier lipids are delivered to the extracellular space by which keratinocyte organelle?
- Lamellar (Odland) body (Correct answer)
- Birbeck granule
- Melanosome
- Keratohyalin granule
Correct answer: Lamellar (Odland) body
Lamellar bodies secrete lipids forming the intercellular barrier of the stratum corneum.
ABD Basic Science and Immunology 3
Melanin is synthesized from which amino acid precursor via the enzyme tyrosinase?