PCB 3233 | PCB3233 Final Exam: Immunology -
University of Central Florida Updated and Latest
Questions and Correct Answers with Rationale
1. A 24-year-old patient presents with a severe reaction to a bee sting, characterized by
respiratory distress and hives. Which immunological component is primarily responsible for
this immediate hypersensitivity reaction?
A. IgE-mediated mast cell degranulation
B. IgG-mediated complement activation
C. T-cell mediated delayed cytotoxicity
D. Immune complex deposition in tissues
Correct Answer: A
Expert Explanation: This clinical presentation describes a Type I hypersensitivity reaction
which is characterized by an immediate response to an allergen. IgE antibodies bind to
high-affinity Fc receptors on the surface of mast cells and basophils. Upon re-exposure to
the bee venom antigen, the IgE molecules are cross-linked, triggering the release of
histamine and leukotrienes. These mediators cause vasodilation, increased vascular
permeability, and smooth muscle contraction in the airways. This pathway is a central
focus of study in the PCB 3233 curriculum regarding allergic disorders.
2. During MHC Class I antigen presentation, which protein is responsible for transporting
processed peptides from the cytosol into the lumen of the endoplasmic reticulum (ER)?
A. TAP (Transporter associated with Antigen Processing)
B. Invariant chain (Ii)
C. HLA-DM
D. Calnexin
Correct Answer: A
Expert Explanation: MHC Class I molecules present endogenous antigens that have been
degraded by the proteasome in the cytosol. The resulting peptides must enter the
endoplasmic reticulum to be loaded onto the MHC Class I molecule. The TAP protein
complex serves as the gatekeeper for this transport process across the ER membrane.
Without functional TAP, MHC Class I molecules remain empty and are eventually degraded.
This mechanism ensures that the immune system can monitor the internal health of every
nucleated cell in the body.
,3. A deficiency in the RAG-1 and RAG-2 enzymes would most likely lead to which of the
following clinical conditions?
A. Chronic Granulomatous Disease
B. Severe Combined Immunodeficiency (SCID)
C. DiGeorge Syndrome
D. Systemic Lupus Erythematosus
Correct Answer: B
Expert Explanation: RAG-1 and RAG-2 are essential enzymes for the V(D)J recombination
process during lymphocyte development. These enzymes are responsible for creating the
double-strand breaks necessary to rearrange gene segments into functional B-cell and T-
cell receptors. A total lack of these enzymes prevents the maturation of any functional B or
T lymphocytes. This condition results in Omenn syndrome or a form of Severe Combined
Immunodeficiency (SCID). Patients with this defect are highly susceptible to life-
threatening infections from birth and require a bone marrow transplant.
4. Which cytokine is primarily responsible for stimulating the proliferation of activated T cells
in an autocrine fashion?
A. IL-2
B. IL-1
C. IL-10
D. TNF-alpha
Correct Answer: A
Expert Explanation: Interleukin-2 (IL-2) is known as the primary T-cell growth factor in
the adaptive immune response. When a T cell is activated by an antigen-presenting cell, it
begins to secrete IL-2 and expresses the high-affinity IL-2 receptor alpha chain (CD25). The
binding of IL-2 to its receptor triggers rapid clonal expansion of that specific T cell
population. This autocrine loop is essential for generating a sufficient number of effector
cells to combat an infection. Many immunosuppressive drugs specifically target this IL-2
pathway to prevent transplant rejection.
5. In the context of the complement system, which of the following components acts as the
main opsonin to enhance phagocytosis?
A. C3b
B. C3a
C. C5a
D. C9
, Correct Answer: A
Expert Explanation: Opsonization is the process by which pathogens are coated with
substances that make them more recognizable to phagocytes. C3b is a major cleavage
product of the complement cascade that binds covalently to the surface of microbes.
Macrophages and neutrophils possess specific receptors (CR1) that recognize and bind to
the C3b molecules. This binding significantly increases the efficiency of engulfment and
subsequent destruction of the pathogen. C3b also plays a role in the formation of the C5
convertase in the later stages of the complement pathway.
6. Natural Killer (NK) cells use which mechanism to identify and kill virally infected or
cancerous cells that have downregulated MHC Class I expression?
A. The ‘Missing Self’ hypothesis
B. Antibody-dependent cellular cytotoxicity (ADCC)
C. Clonal selection
D. T-cell receptor recognition
Correct Answer: A
Expert Explanation: NK cells are innate immune cells that monitor the expression of MHC
Class I molecules on the surface of body cells. Under normal conditions, inhibitory
receptors on NK cells bind to MHC Class I, preventing the NK cell from attacking. Many
viruses and tumors downregulate MHC Class I to evade detection by Cytotoxic T
Lymphocytes (CTLs). The absence of this inhibitory signal allows the NK cell’s activating
receptors to trigger the release of perforin and granzymes. This strategy, known as the
‘Missing Self’ hypothesis, ensures that cells trying to hide from the adaptive immune
system are still targeted.
7. A patient with systemic lupus erythematosus (SLE) has high levels of immune complexes
circulating in the blood, leading to glomerulonephritis. This is an example of which type of
hypersensitivity?
A. Type I
B. Type II
C. Type IV
D. Type III
Correct Answer: D
Expert Explanation: Type III hypersensitivity involves the formation of antigen-antibody
complexes that are not efficiently cleared by the reticuloendothelial system. These
complexes deposit in various tissues, such as the basement membrane of the kidneys or
blood vessel walls. Once deposited, they activate the complement system, leading to the
recruitment of neutrophils and local tissue damage. SLE is a classic example of this
University of Central Florida Updated and Latest
Questions and Correct Answers with Rationale
1. A 24-year-old patient presents with a severe reaction to a bee sting, characterized by
respiratory distress and hives. Which immunological component is primarily responsible for
this immediate hypersensitivity reaction?
A. IgE-mediated mast cell degranulation
B. IgG-mediated complement activation
C. T-cell mediated delayed cytotoxicity
D. Immune complex deposition in tissues
Correct Answer: A
Expert Explanation: This clinical presentation describes a Type I hypersensitivity reaction
which is characterized by an immediate response to an allergen. IgE antibodies bind to
high-affinity Fc receptors on the surface of mast cells and basophils. Upon re-exposure to
the bee venom antigen, the IgE molecules are cross-linked, triggering the release of
histamine and leukotrienes. These mediators cause vasodilation, increased vascular
permeability, and smooth muscle contraction in the airways. This pathway is a central
focus of study in the PCB 3233 curriculum regarding allergic disorders.
2. During MHC Class I antigen presentation, which protein is responsible for transporting
processed peptides from the cytosol into the lumen of the endoplasmic reticulum (ER)?
A. TAP (Transporter associated with Antigen Processing)
B. Invariant chain (Ii)
C. HLA-DM
D. Calnexin
Correct Answer: A
Expert Explanation: MHC Class I molecules present endogenous antigens that have been
degraded by the proteasome in the cytosol. The resulting peptides must enter the
endoplasmic reticulum to be loaded onto the MHC Class I molecule. The TAP protein
complex serves as the gatekeeper for this transport process across the ER membrane.
Without functional TAP, MHC Class I molecules remain empty and are eventually degraded.
This mechanism ensures that the immune system can monitor the internal health of every
nucleated cell in the body.
,3. A deficiency in the RAG-1 and RAG-2 enzymes would most likely lead to which of the
following clinical conditions?
A. Chronic Granulomatous Disease
B. Severe Combined Immunodeficiency (SCID)
C. DiGeorge Syndrome
D. Systemic Lupus Erythematosus
Correct Answer: B
Expert Explanation: RAG-1 and RAG-2 are essential enzymes for the V(D)J recombination
process during lymphocyte development. These enzymes are responsible for creating the
double-strand breaks necessary to rearrange gene segments into functional B-cell and T-
cell receptors. A total lack of these enzymes prevents the maturation of any functional B or
T lymphocytes. This condition results in Omenn syndrome or a form of Severe Combined
Immunodeficiency (SCID). Patients with this defect are highly susceptible to life-
threatening infections from birth and require a bone marrow transplant.
4. Which cytokine is primarily responsible for stimulating the proliferation of activated T cells
in an autocrine fashion?
A. IL-2
B. IL-1
C. IL-10
D. TNF-alpha
Correct Answer: A
Expert Explanation: Interleukin-2 (IL-2) is known as the primary T-cell growth factor in
the adaptive immune response. When a T cell is activated by an antigen-presenting cell, it
begins to secrete IL-2 and expresses the high-affinity IL-2 receptor alpha chain (CD25). The
binding of IL-2 to its receptor triggers rapid clonal expansion of that specific T cell
population. This autocrine loop is essential for generating a sufficient number of effector
cells to combat an infection. Many immunosuppressive drugs specifically target this IL-2
pathway to prevent transplant rejection.
5. In the context of the complement system, which of the following components acts as the
main opsonin to enhance phagocytosis?
A. C3b
B. C3a
C. C5a
D. C9
, Correct Answer: A
Expert Explanation: Opsonization is the process by which pathogens are coated with
substances that make them more recognizable to phagocytes. C3b is a major cleavage
product of the complement cascade that binds covalently to the surface of microbes.
Macrophages and neutrophils possess specific receptors (CR1) that recognize and bind to
the C3b molecules. This binding significantly increases the efficiency of engulfment and
subsequent destruction of the pathogen. C3b also plays a role in the formation of the C5
convertase in the later stages of the complement pathway.
6. Natural Killer (NK) cells use which mechanism to identify and kill virally infected or
cancerous cells that have downregulated MHC Class I expression?
A. The ‘Missing Self’ hypothesis
B. Antibody-dependent cellular cytotoxicity (ADCC)
C. Clonal selection
D. T-cell receptor recognition
Correct Answer: A
Expert Explanation: NK cells are innate immune cells that monitor the expression of MHC
Class I molecules on the surface of body cells. Under normal conditions, inhibitory
receptors on NK cells bind to MHC Class I, preventing the NK cell from attacking. Many
viruses and tumors downregulate MHC Class I to evade detection by Cytotoxic T
Lymphocytes (CTLs). The absence of this inhibitory signal allows the NK cell’s activating
receptors to trigger the release of perforin and granzymes. This strategy, known as the
‘Missing Self’ hypothesis, ensures that cells trying to hide from the adaptive immune
system are still targeted.
7. A patient with systemic lupus erythematosus (SLE) has high levels of immune complexes
circulating in the blood, leading to glomerulonephritis. This is an example of which type of
hypersensitivity?
A. Type I
B. Type II
C. Type IV
D. Type III
Correct Answer: D
Expert Explanation: Type III hypersensitivity involves the formation of antigen-antibody
complexes that are not efficiently cleared by the reticuloendothelial system. These
complexes deposit in various tissues, such as the basement membrane of the kidneys or
blood vessel walls. Once deposited, they activate the complement system, leading to the
recruitment of neutrophils and local tissue damage. SLE is a classic example of this
