CMLA Immunology & Serology 2 — Questions and Answers
Question 1: What principle does the ELISA (Enzyme-Linked Immunosorbent Assay) use to detect antibodies or antigens?
- Precipitation of immune complexes in agar
- Enzyme-labeled antibodies producing a colorimetric signal (Correct answer)
- Fluorescent dyes visualized under UV light
- Agglutination of sensitized red blood cells
Correct answer: Enzyme-labeled antibodies producing a colorimetric signal
ELISA uses enzyme-conjugated antibodies that catalyze a substrate reaction, producing a measurable color change proportional to antigen or antibody concentration.
Question 2: In serological testing, agglutination indicates:
- Lysis of cells by complement activation
- Cross-linking of particulate antigens by antibodies causing visible clumping (Correct answer)
- Precipitation of soluble antigen-antibody complexes
- Viral neutralization by specific antibodies
Correct answer: Cross-linking of particulate antigens by antibodies causing visible clumping
Agglutination occurs when antibodies form bridges between multiple particulate antigens (bacteria, red blood cells), causing visible clumping.
Question 3: What is the purpose of including a positive control in a serological assay?
- To ensure reagents are free from contamination
- To verify the test system produces a positive result with known positive material (Correct answer)
- To calibrate spectrophotometer readings
- To identify non-specific background binding
Correct answer: To verify the test system produces a positive result with known positive material
A positive control confirms the assay is functioning correctly by demonstrating it can produce the expected positive result with a known positive specimen.
Question 4: In indirect fluorescent antibody (IFA) testing, the fluorescent-labeled secondary antibody binds to:
- The target antigen on the substrate directly
- The patient's primary antibody already bound to antigen (Correct answer)
- The substrate membrane
- The cell surface receptors
Correct answer: The patient's primary antibody already bound to antigen
In IFA, the fluorescent secondary antibody binds to the patient's (primary) antibody, which is already complexed with the antigen on the substrate.
Question 5: What does a serum antibody titer measure?
- The total protein concentration in serum
- The highest dilution of serum still showing a positive reaction (Correct answer)
- The rate of antibody synthesis per hour
- The molecular weight of the detected antibody
Correct answer: The highest dilution of serum still showing a positive reaction
A titer is the reciprocal of the highest serum dilution that still yields a detectable (positive) reaction, reflecting relative antibody concentration.
Question 6: Which non-treponemal test is used as a screening test for syphilis?
- Weil-Felix test
- RPR (Rapid Plasma Reagin) (Correct answer)
- Westergren ESR test
- Direct Coombs test
Correct answer: RPR (Rapid Plasma Reagin)
The RPR is a non-treponemal flocculation test that detects reagin antibodies against cardiolipin-lecithin-cholesterol antigen, used for syphilis screening.
Question 7: In a precipitation reaction, the zone of equivalence refers to:
- The pH optimum for antigen-antibody binding
- The point where antigen and antibody concentrations allow maximum lattice formation and precipitation (Correct answer)
- The temperature at which precipitation occurs
- The complement concentration needed for lysis
Correct answer: The point where antigen and antibody concentrations allow maximum lattice formation and precipitation
The zone of equivalence is where antigen and antibody are in optimal proportions, forming large cross-linked lattices that precipitate out of solution.
CMLA Immunology & Serology 2
What principle does the ELISA (Enzyme-Linked Immunosorbent Assay) use to detect antibodies or antigens?