COMSAE PHASE 1 IMMUNOLOGY PRACTICE
EXAM WITH ACTUAL QUESTIONS AND
VERIFIED ANSWERS, PLUS EXPLAINED
RATIONALES/EXPERT VERIFIED FOR
GUARANTEED 100% PASS 2026/LATEST
UPDATE/INSTANT DOWNLOAD PDF
Question 1
A 24-year-old man develops recurrent episodes of Neisseria
meningitidis bacteremia. He has normal numbers of B cells, T cells, and
neutrophils. Serum immunoglobulin concentrations are normal. Genetic
testing identifies a deficiency involving a terminal component of the
complement cascade. Which immunologic abnormality best explains his
susceptibility?
A. Impaired opsonization of encapsulated bacteria
B. Failure of classical complement activation by antigen-antibody
complexes
C. Defective formation of the membrane attack complex
D. Impaired neutrophil respiratory burst
E. Reduced generation of thymic T cells
Answer: C. Defective formation of the membrane attack complex
Rationale: Terminal complement components C5b-C9 form the
membrane attack complex (MAC), which is particularly important for
killing Neisseria species. Deficiencies of C5-C9 classically predispose
to recurrent Neisseria infections. In contrast, C3 deficiency produces
severe recurrent infections with encapsulated organisms because C3b-
mediated opsonization is impaired.
Question 2
1
,A 7-year-old child has recurrent sinopulmonary infections caused by
encapsulated bacteria. Laboratory testing shows markedly decreased
serum IgG, IgA, and IgM. Flow cytometry demonstrates normal
numbers of mature B cells but very few plasma cells. Which process is
most likely defective?
A. V(D)J recombination in developing B cells
B. Differentiation of activated B cells into antibody-secreting plasma
cells
C. Positive selection of thymocytes
D. Complement-mediated lysis
E. Neutrophil chemotaxis
Answer: B. Differentiation of activated B cells into antibody-
secreting plasma cells
Rationale: Normal mature B-cell numbers with severe
hypogammaglobulinemia suggests a defect in B-cell differentiation
into plasma cells or antibody production rather than failure of B-cell
development. Plasma cells are terminally differentiated B cells
responsible for high-volume immunoglobulin secretion.
Question 3
A patient receives a booster vaccination against tetanus. Several days
later, serum antibody concentration rises dramatically, with most
antibodies having high affinity for the antigen. Which immunologic
mechanism is primarily responsible?
A. Activation of naïve T cells
B. Somatic hypermutation and clonal selection of memory B cells
C. Increased activity of natural killer cells
D. Generation of new thymic epithelial cells
E. Complement-independent phagocytosis
2
,Answer: B. Somatic hypermutation and clonal selection of memory
B cells
Rationale: A secondary immune response is faster and stronger
because antigen-specific memory B cells rapidly proliferate and
differentiate. Somatic hypermutation followed by affinity selection
produces antibodies with increased antigen affinity. Class switching
also allows production of appropriate antibody isotypes.
Question 4
A 3-year-old child develops recurrent viral, fungal, and opportunistic
bacterial infections. Laboratory studies reveal profound lymphopenia
involving both CD4+ and CD8+ T cells. B-cell numbers are also
markedly decreased. Which developmental process is most likely
impaired?
A. Immunoglobulin class switching
B. Neutrophil oxidative burst
C. Thymic positive selection only
D. Common lymphoid progenitor development
E. Terminal complement activation
Answer: D. Common lymphoid progenitor development
Rationale: Severe combined immunodeficiency involving both T- and
B-cell compartments can result from defects affecting early lymphoid
development. A defect in common lymphoid progenitor formation can
markedly reduce both lymphocyte populations. Such patients are
susceptible to viral, bacterial, fungal, and opportunistic infections.
Question 5
3
, A macrophage encounters intracellular Mycobacterium tuberculosis.
Which cytokine produced by activated T-helper cells is most important
for activating the macrophage's microbicidal mechanisms?
A. IL-4
B. IL-5
C. IL-10
D. IL-17
E. IFN-γ
Answer: E. IFN-γ
Rationale: Th1 cells produce IFN-γ, which strongly activates
macrophages and enhances intracellular killing. IL-4 promotes Th2
differentiation and IgE responses, IL-5 promotes eosinophil activity,
IL-10 suppresses macrophage activation, and IL-17 promotes
neutrophil recruitment.
Question 6
A researcher studies antigen presentation to CD8+ cytotoxic T
lymphocytes. A viral protein synthesized inside an infected cell is
degraded into peptides and transported into the endoplasmic reticulum.
Which molecule transports these peptides?
A. TAP
B. CD28
C. ICAM-1
D. Cathepsin D
E. Fc receptor
Answer: A. TAP
Rationale: Cytosolic proteins are degraded by the proteasome, and
resulting peptides are transported into the endoplasmic reticulum by
TAP (transporter associated with antigen processing). Peptides then
4
EXAM WITH ACTUAL QUESTIONS AND
VERIFIED ANSWERS, PLUS EXPLAINED
RATIONALES/EXPERT VERIFIED FOR
GUARANTEED 100% PASS 2026/LATEST
UPDATE/INSTANT DOWNLOAD PDF
Question 1
A 24-year-old man develops recurrent episodes of Neisseria
meningitidis bacteremia. He has normal numbers of B cells, T cells, and
neutrophils. Serum immunoglobulin concentrations are normal. Genetic
testing identifies a deficiency involving a terminal component of the
complement cascade. Which immunologic abnormality best explains his
susceptibility?
A. Impaired opsonization of encapsulated bacteria
B. Failure of classical complement activation by antigen-antibody
complexes
C. Defective formation of the membrane attack complex
D. Impaired neutrophil respiratory burst
E. Reduced generation of thymic T cells
Answer: C. Defective formation of the membrane attack complex
Rationale: Terminal complement components C5b-C9 form the
membrane attack complex (MAC), which is particularly important for
killing Neisseria species. Deficiencies of C5-C9 classically predispose
to recurrent Neisseria infections. In contrast, C3 deficiency produces
severe recurrent infections with encapsulated organisms because C3b-
mediated opsonization is impaired.
Question 2
1
,A 7-year-old child has recurrent sinopulmonary infections caused by
encapsulated bacteria. Laboratory testing shows markedly decreased
serum IgG, IgA, and IgM. Flow cytometry demonstrates normal
numbers of mature B cells but very few plasma cells. Which process is
most likely defective?
A. V(D)J recombination in developing B cells
B. Differentiation of activated B cells into antibody-secreting plasma
cells
C. Positive selection of thymocytes
D. Complement-mediated lysis
E. Neutrophil chemotaxis
Answer: B. Differentiation of activated B cells into antibody-
secreting plasma cells
Rationale: Normal mature B-cell numbers with severe
hypogammaglobulinemia suggests a defect in B-cell differentiation
into plasma cells or antibody production rather than failure of B-cell
development. Plasma cells are terminally differentiated B cells
responsible for high-volume immunoglobulin secretion.
Question 3
A patient receives a booster vaccination against tetanus. Several days
later, serum antibody concentration rises dramatically, with most
antibodies having high affinity for the antigen. Which immunologic
mechanism is primarily responsible?
A. Activation of naïve T cells
B. Somatic hypermutation and clonal selection of memory B cells
C. Increased activity of natural killer cells
D. Generation of new thymic epithelial cells
E. Complement-independent phagocytosis
2
,Answer: B. Somatic hypermutation and clonal selection of memory
B cells
Rationale: A secondary immune response is faster and stronger
because antigen-specific memory B cells rapidly proliferate and
differentiate. Somatic hypermutation followed by affinity selection
produces antibodies with increased antigen affinity. Class switching
also allows production of appropriate antibody isotypes.
Question 4
A 3-year-old child develops recurrent viral, fungal, and opportunistic
bacterial infections. Laboratory studies reveal profound lymphopenia
involving both CD4+ and CD8+ T cells. B-cell numbers are also
markedly decreased. Which developmental process is most likely
impaired?
A. Immunoglobulin class switching
B. Neutrophil oxidative burst
C. Thymic positive selection only
D. Common lymphoid progenitor development
E. Terminal complement activation
Answer: D. Common lymphoid progenitor development
Rationale: Severe combined immunodeficiency involving both T- and
B-cell compartments can result from defects affecting early lymphoid
development. A defect in common lymphoid progenitor formation can
markedly reduce both lymphocyte populations. Such patients are
susceptible to viral, bacterial, fungal, and opportunistic infections.
Question 5
3
, A macrophage encounters intracellular Mycobacterium tuberculosis.
Which cytokine produced by activated T-helper cells is most important
for activating the macrophage's microbicidal mechanisms?
A. IL-4
B. IL-5
C. IL-10
D. IL-17
E. IFN-γ
Answer: E. IFN-γ
Rationale: Th1 cells produce IFN-γ, which strongly activates
macrophages and enhances intracellular killing. IL-4 promotes Th2
differentiation and IgE responses, IL-5 promotes eosinophil activity,
IL-10 suppresses macrophage activation, and IL-17 promotes
neutrophil recruitment.
Question 6
A researcher studies antigen presentation to CD8+ cytotoxic T
lymphocytes. A viral protein synthesized inside an infected cell is
degraded into peptides and transported into the endoplasmic reticulum.
Which molecule transports these peptides?
A. TAP
B. CD28
C. ICAM-1
D. Cathepsin D
E. Fc receptor
Answer: A. TAP
Rationale: Cytosolic proteins are degraded by the proteasome, and
resulting peptides are transported into the endoplasmic reticulum by
TAP (transporter associated with antigen processing). Peptides then
4
