Laboratory Science Immunology and Serology 2 — Questions and Answers
Question 1: What does a positive monospot (heterophile antibody) test indicate?
- HIV infection
- Cytomegalovirus infection
- Infectious mononucleosis (Epstein-Barr virus) (Correct answer)
- Streptococcal pharyngitis
Correct answer: Infectious mononucleosis (Epstein-Barr virus)
The monospot test detects heterophile antibodies produced during EBV-caused infectious mononucleosis; these IgM antibodies agglutinate horse or sheep RBCs in the rapid latex test.
Question 2: Which CD marker is used to identify T helper lymphocytes, and its count monitors HIV/AIDS progression?
- CD8
- CD19
- CD4 (Correct answer)
- CD56
Correct answer: CD4
CD4+ T helper cells are the primary target of HIV; CD4 count monitors immune status, with counts <200 cells/µL defining AIDS and increasing risk of opportunistic infections.
Question 3: What is the ELISA test principle used in serology?
- Agglutination of red blood cells
- Enzyme-linked antibody detecting antigen-antibody reactions via color change (Correct answer)
- Electrical migration of proteins in gel
- Radioactive labeling of antigens
Correct answer: Enzyme-linked antibody detecting antigen-antibody reactions via color change
ELISA uses enzyme-conjugated antibodies; when the target antigen or antibody is present, substrate is cleaved by the enzyme producing a measurable color change proportional to the concentration.
Question 4: Which complement pathway is activated by antigen-antibody complexes (IgG or IgM)?
- Alternative pathway
- Lectin pathway
- Classical pathway (Correct answer)
- Regulatory pathway
Correct answer: Classical pathway
The classical complement pathway is initiated by C1q binding to Fc regions of antigen-bound IgG or IgM, triggering the C1-C2-C4 cascade and ultimately forming the membrane attack complex.
Question 5: A Western blot test in HIV diagnosis detects antibodies to which viral proteins?
- Only envelope proteins gp120 and gp41
- Structural proteins: gag (p24, p17), pol (p31, p51, p66), and env (gp41, gp120/160) (Correct answer)
- Core protein p24 only
- Reverse transcriptase only
Correct answer: Structural proteins: gag (p24, p17), pol (p31, p51, p66), and env (gp41, gp120/160)
HIV Western blot detects antibodies to multiple viral proteins; CDC criteria for positivity require bands for at least two of p24, gp41, and gp120/160 to confirm HIV infection.
Question 6: What does the C-reactive protein (CRP) test measure?
- Complement C1 levels
- An acute-phase protein produced by the liver in response to inflammation or infection (Correct answer)
- Antibodies to streptococcal antigens
- Red blood cell turnover rate
Correct answer: An acute-phase protein produced by the liver in response to inflammation or infection
CRP is a pentraxin produced by the liver in response to IL-6 during acute inflammation; elevated CRP is a sensitive but nonspecific marker of infection, inflammation, or tissue injury.
Laboratory Science Immunology and Serology 2
What does a positive monospot (heterophile antibody) test indicate?