PCB 3233 Exam 4 V2 | PCB 3233
Immunology | Actual Q&A with Rationale
(PCB3233 Exam 4) | University of Central
Florida
1. Which immunoglobulin isotype is the primary mediator of Type I hypersensitivity
reactions?
A. IgG
B. IgE
C. IgM
D. IgA
Answer: B
Rationale: IgE is the specific antibody responsible for immediate hypersensitivity
reactions by binding to FceRI receptors on mast cells and basophils. Upon cross-linking by
an allergen, these cells degranulate and release vasoactive amines like histamine. This
isotype is typically found at very low levels in the serum compared to IgG but is potent in
triggering allergic responses.
2. In the context of Type II hypersensitivity, which mechanism leads to the destruction of
target cells?
A. Complement-mediated lysis or Antibody-Dependent Cell-mediated Cytotoxicity (ADCC)
,B. Immune complex deposition in small vessels
C. Delayed-type hypersensitivity mediated by Th1 cells
D. Degranulation of eosinophils via IgE binding
Answer: A
Rationale: Type II hypersensitivity involves IgG or IgM antibodies binding to antigens on
the surface of specific cells or tissues. This binding can activate the classical complement
pathway, leading to the formation of the membrane attack complex. Additionally, it can
recruit NK cells or macrophages to destroy the target cell through ADCC mechanisms.
3. Systemic Lupus Erythematosus (SLE) is characterized by the deposition of immune
complexes, making it which type of hypersensitivity?
A. Type I
B. Type III
C. Type II
D. Type IV
Answer: B
Rationale: Type III hypersensitivity is defined by the formation of small, soluble antigen-
antibody complexes that are not effectively cleared from the circulation. These complexes
deposit in basement membranes of various organs, such as the kidneys and joints, where
they trigger inflammation and tissue damage. In SLE, the presence of anti-dsDNA
, antibodies leads to chronic immune complex formation and widespread systemic
symptoms.
4. What is the primary cellular mediator responsible for the delayed-type hypersensitivity
(DTH) response observed in the Tuberculin skin test?
A. Mast cells
B. Th1 cells and Macrophages
C. B lymphocytes
D. Basophils
Answer: B
Rationale: DTH reactions are classified as Type IV hypersensitivity, which does not involve
antibodies but rather T cells. Upon secondary exposure to Mycobacterium tuberculosis
antigens, memory Th1 cells secrete IFN-gamma to activate macrophages. These activated
macrophages then cause the localized induration and inflammation seen 48 to 72 hours
after the test.
5. Which gene is essential for the expression of tissue-specific antigens in the thymus to
facilitate central tolerance?
A. STAT6
B. FoxP3
C. RAG1
Immunology | Actual Q&A with Rationale
(PCB3233 Exam 4) | University of Central
Florida
1. Which immunoglobulin isotype is the primary mediator of Type I hypersensitivity
reactions?
A. IgG
B. IgE
C. IgM
D. IgA
Answer: B
Rationale: IgE is the specific antibody responsible for immediate hypersensitivity
reactions by binding to FceRI receptors on mast cells and basophils. Upon cross-linking by
an allergen, these cells degranulate and release vasoactive amines like histamine. This
isotype is typically found at very low levels in the serum compared to IgG but is potent in
triggering allergic responses.
2. In the context of Type II hypersensitivity, which mechanism leads to the destruction of
target cells?
A. Complement-mediated lysis or Antibody-Dependent Cell-mediated Cytotoxicity (ADCC)
,B. Immune complex deposition in small vessels
C. Delayed-type hypersensitivity mediated by Th1 cells
D. Degranulation of eosinophils via IgE binding
Answer: A
Rationale: Type II hypersensitivity involves IgG or IgM antibodies binding to antigens on
the surface of specific cells or tissues. This binding can activate the classical complement
pathway, leading to the formation of the membrane attack complex. Additionally, it can
recruit NK cells or macrophages to destroy the target cell through ADCC mechanisms.
3. Systemic Lupus Erythematosus (SLE) is characterized by the deposition of immune
complexes, making it which type of hypersensitivity?
A. Type I
B. Type III
C. Type II
D. Type IV
Answer: B
Rationale: Type III hypersensitivity is defined by the formation of small, soluble antigen-
antibody complexes that are not effectively cleared from the circulation. These complexes
deposit in basement membranes of various organs, such as the kidneys and joints, where
they trigger inflammation and tissue damage. In SLE, the presence of anti-dsDNA
, antibodies leads to chronic immune complex formation and widespread systemic
symptoms.
4. What is the primary cellular mediator responsible for the delayed-type hypersensitivity
(DTH) response observed in the Tuberculin skin test?
A. Mast cells
B. Th1 cells and Macrophages
C. B lymphocytes
D. Basophils
Answer: B
Rationale: DTH reactions are classified as Type IV hypersensitivity, which does not involve
antibodies but rather T cells. Upon secondary exposure to Mycobacterium tuberculosis
antigens, memory Th1 cells secrete IFN-gamma to activate macrophages. These activated
macrophages then cause the localized induration and inflammation seen 48 to 72 hours
after the test.
5. Which gene is essential for the expression of tissue-specific antigens in the thymus to
facilitate central tolerance?
A. STAT6
B. FoxP3
C. RAG1
