Medical Laboratory Technician Exam Immunology and Serology 5 — Questions and Answers
Question 1: Which type of hypersensitivity reaction is responsible for contact dermatitis caused by poison ivy?
- Type I – IgE-mediated
- Type II – cytotoxic
- Type III – immune complex
- Type IV – delayed-type (cell-mediated) (Correct answer)
Correct answer: Type IV – delayed-type (cell-mediated)
Contact dermatitis is a Type IV (delayed-type) hypersensitivity reaction mediated by sensitized T lymphocytes, not antibodies.
Question 2: A positive tuberculin (PPD) skin test reaction is read at 48–72 hours and is an example of which immune mechanism?
- Complement-mediated lysis
- IgE-mediated degranulation
- T cell–mediated delayed hypersensitivity (Correct answer)
- Immune complex deposition
Correct answer: T cell–mediated delayed hypersensitivity
PPD testing relies on Type IV delayed hypersensitivity; sensitized CD4+ T cells release cytokines causing induration at the injection site.
Question 3: Which of the following is a characteristic of the alternative pathway of complement activation?
- Requires C1q, C1r, and C1s
- Is initiated by antigen-antibody complexes
- Is spontaneously activated on microbial surfaces lacking regulatory proteins (Correct answer)
- Requires mannose-binding lectin
Correct answer: Is spontaneously activated on microbial surfaces lacking regulatory proteins
The alternative pathway activates spontaneously via continuous low-level C3 hydrolysis and amplifies on surfaces lacking complement regulatory proteins.
Question 4: Anti-centromere antibodies detected by ANA testing are most specifically associated with which disease?
- Systemic lupus erythematosus
- Limited cutaneous systemic sclerosis (CREST syndrome) (Correct answer)
- Sjögren's syndrome
- Polymyositis
Correct answer: Limited cutaneous systemic sclerosis (CREST syndrome)
Anti-centromere antibodies are highly specific for limited cutaneous systemic sclerosis (CREST syndrome).
Question 5: In flow cytometry, fluorochromes are excited by which energy source?
- Ultraviolet lamp
- Laser beam (Correct answer)
- Radioactive isotope
- Chemiluminescent substrate
Correct answer: Laser beam
Flow cytometers use one or more lasers to excite fluorochromes conjugated to antibodies, and detectors measure emitted fluorescence.
Question 6: A patient with recurrent sinopulmonary infections, normal B and T cell counts, but absent germinal centers and low IgG/IgA/IgM most likely has:
- X-linked agammaglobulinemia
- Common variable immunodeficiency (CVID) (Correct answer)
- Hyper-IgM syndrome
- Transient hypogammaglobulinemia of infancy
Correct answer: Common variable immunodeficiency (CVID)
CVID is characterized by low immunoglobulins with normal B and T cell numbers but defective antibody production, typically presenting in young adults.
Question 7: In an indirect fluorescent antibody (IFA) test, the patient's antibody is detected using:
- A labeled antigen specific for the antibody
- A fluorescently labeled anti-human immunoglobulin (Correct answer)
- A radiolabeled complement component
- An enzyme-conjugated antigen
Correct answer: A fluorescently labeled anti-human immunoglobulin
IFA uses a fluorescently labeled secondary antibody (anti-human Ig) to detect patient antibody bound to substrate antigen.
Medical Laboratory Technician Exam Immunology and Serology 5
Which type of hypersensitivity reaction is responsible for contact dermatitis caused by poison ivy?