MLPAO MLPAO Immunology and Serology 1 — Questions and Answers
Question 1: Which immunoglobulin class is the first to be produced during a primary immune response?
- IgG
- IgM (Correct answer)
- IgA
- IgE
Correct answer: IgM
IgM is the first antibody class produced during a primary immune response due to its pentameric structure that allows effective complement activation before affinity maturation occurs.
Question 2: In the complement system, which pathway is activated by antigen-antibody complexes?
- Lectin pathway
- Alternative pathway
- Classical pathway (Correct answer)
- Mannose-binding pathway
Correct answer: Classical pathway
The classical pathway is activated by antigen-antibody (immune) complexes when IgG or IgM antibodies bind to C1q, initiating the complement cascade.
Question 3: A patient's serum is tested by ELISA for HIV antibodies. Which component is coated onto the microplate wells?
- Patient antibodies
- Enzyme-conjugated secondary antibody
- HIV antigens (Correct answer)
- Complement proteins
Correct answer: HIV antigens
In an indirect ELISA for antibody detection, the target antigen (HIV proteins) is coated onto the plate to capture any specific antibodies present in the patient's serum.
Question 4: Which type of hypersensitivity reaction is responsible for anaphylaxis?
- Type II (cytotoxic)
- Type III (immune complex)
- Type IV (delayed)
- Type I (immediate) (Correct answer)
Correct answer: Type I (immediate)
Type I (immediate) hypersensitivity is IgE-mediated and causes mast cell degranulation, releasing histamine and other mediators that produce anaphylaxis within minutes.
Question 5: The prozone phenomenon in serology occurs when:
- Antigen concentration is too low to form any complexes
- Antibody is in great excess, preventing lattice formation (Correct answer)
- The temperature is too high for binding
- Complement is depleted from the sample
Correct answer: Antibody is in great excess, preventing lattice formation
Prozone occurs when antibody is in great excess relative to antigen, causing all antigen sites to be occupied by individual antibodies rather than forming the cross-linked lattice needed for visible agglutination.
Question 6: Which cell type is responsible for producing antibodies?
- Cytotoxic T lymphocytes
- Natural killer cells
- Plasma cells (Correct answer)
- Macrophages
Correct answer: Plasma cells
Plasma cells are terminally differentiated B lymphocytes specifically designed to produce and secrete large quantities of antibodies.
Question 7: A direct Coombs test (direct antiglobulin test) detects:
- Free antibodies in patient serum
- Antibodies bound to patient's red blood cells in vivo (Correct answer)
- Complement proteins in the patient's plasma
- Antigens on donor red blood cells
Correct answer: Antibodies bound to patient's red blood cells in vivo
The direct antiglobulin test detects IgG or complement already bound to the patient's red blood cells in vivo, as occurs in autoimmune hemolytic anemia or hemolytic transfusion reactions.
MLPAO MLPAO Immunology and Serology 1
Which immunoglobulin class is the first to be produced during a primary immune response?