Medical Laboratory TechnicianĀ Exam Immunology and Serology 3 ā Questions and Answers
Question 1: Which test is considered the gold standard confirmatory test for HIV infection?
- ELISA antibody screen
- Western blot / immunoblot (Correct answer)
- p24 antigen assay
- CD4+ T cell count
Correct answer: Western blot / immunoblot
Western blot (or newer HIV-1/HIV-2 differentiation immunoassay) is used to confirm a repeatedly reactive HIV screen result.
Question 2: A latex agglutination test for Cryptococcus neoformans detects which antigen?
- Beta-glucan cell wall component
- Polysaccharide capsular antigen (Correct answer)
- Ergosterol membrane lipid
- Chitin synthase enzyme
Correct answer: Polysaccharide capsular antigen
The cryptococcal antigen test detects polysaccharide capsular antigen of C. neoformans in serum or CSF.
Question 3: Secretory IgA differs from serum IgA primarily in that secretory IgA:
- Is a monomer
- Contains a J chain and secretory component (Correct answer)
- Is produced by plasma cells in bone marrow
- Activates complement via the classical pathway
Correct answer: Contains a J chain and secretory component
Secretory IgA is a dimer joined by a J chain and protected by a secretory component added during transcytosis across epithelial cells.
Question 4: In immunofluorescence testing for ANA, a homogeneous (diffuse) pattern is most commonly associated with antibodies against:
- Sm antigen
- dsDNA and histones (Correct answer)
- SS-A (Ro)
- Centromere proteins
Correct answer: dsDNA and histones
A homogeneous ANA pattern reflects antibodies to dsDNA and histones that bind uniformly throughout the nucleus.
Question 5: Which immunoglobulin class is the first to be produced during a primary immune response?
- IgG
- IgA
- IgM (Correct answer)
- IgE
Correct answer: IgM
IgM is synthesized first during a primary immune response because it requires no class-switch recombination.
Question 6: A patient with recurrent Neisseria infections and low CH50 but normal C3 levels most likely has a deficiency of:
- C1q
- C3
- Terminal complement components (C5āC9) (Correct answer)
- Factor B
Correct answer: Terminal complement components (C5āC9)
Terminal complement deficiency (C5āC9) impairs membrane attack complex formation, predisposing to Neisseria bacteremia, with low CH50 but normal C3.
Question 7: The Weil-Felix test uses Proteus OX strains to detect antibodies in which infection?
- Typhoid fever
- Rocky Mountain spotted fever (Rickettsia) (Correct answer)
- Brucellosis
- Lyme disease
Correct answer: Rocky Mountain spotted fever (Rickettsia)
The Weil-Felix test exploits cross-reactive antigens between Proteus OX strains and Rickettsia species to detect rickettsial antibodies.
Medical Laboratory TechnicianĀ Exam Immunology and Serology 3
Which test is considered the gold standard confirmatory test for HIV infection?