Medical Laboratory Technician Exam Immunology and Serology 2 — Questions and Answers
Question 1: Which complement pathway is activated by mannose-binding lectin (MBL) binding to microbial carbohydrates?
- Classical pathway
- Lectin pathway (Correct answer)
- Alternative pathway
- Terminal pathway
Correct answer: Lectin pathway
MBL activates the lectin (MBL) pathway by binding mannose residues on microbial surfaces, triggering MASP-1 and MASP-2.
Question 2: A patient's serum shows a prozone phenomenon in an RPR test. What should the laboratory do?
- Report the result as negative
- Dilute the serum and repeat the test (Correct answer)
- Confirm with a treponemal test immediately
- Repeat using undiluted serum twice
Correct answer: Dilute the serum and repeat the test
Prozone occurs with antibody excess; diluting the serum allows lattice formation and produces a visible agglutination reaction.
Question 3: Which cell type is the primary producer of IgE antibodies in allergic responses?
- Plasma cells derived from B lymphocytes (Correct answer)
- Mast cells
- Eosinophils
- NK cells
Correct answer: Plasma cells derived from B lymphocytes
IgE is secreted by plasma cells (terminally differentiated B cells) after class-switching driven by IL-4 and IL-13.
Question 4: In a direct antiglobulin test (DAT), a positive result with anti-IgG but negative with anti-C3d most likely indicates:
- Cold autoimmune hemolytic anemia
- Warm autoimmune hemolytic anemia (Correct answer)
- Paroxysmal cold hemoglobinuria
- Drug-induced hemolysis via immune complex mechanism
Correct answer: Warm autoimmune hemolytic anemia
Warm AIHA is predominantly IgG-mediated without complement deposition, yielding a positive anti-IgG DAT only.
Question 5: Which cytokine is the primary inducer of acute-phase protein synthesis in the liver?
- IL-2
- TNF-alpha
- IL-6 (Correct answer)
- IFN-gamma
Correct answer: IL-6
IL-6 is the principal cytokine that stimulates hepatocytes to produce acute-phase proteins such as CRP and fibrinogen.
Question 6: A VDRL test performed on CSF is used to diagnose which condition?
- Congenital syphilis in neonates
- Neurosyphilis (Correct answer)
- Primary syphilis
- Latent syphilis
Correct answer: Neurosyphilis
VDRL on CSF is the standard serologic test for diagnosing neurosyphilis, as it has high specificity in that specimen type.
Question 7: HLA typing is most critical before which clinical procedure?
- Autologous blood transfusion
- Solid organ transplantation (Correct answer)
- Platelet apheresis donation
- Bone marrow biopsy
Correct answer: Solid organ transplantation
HLA matching between donor and recipient is essential in solid organ transplantation to minimize rejection risk.
