QIHC 2026 STUDY GUIDE Qualification
Immunohistochemistry Practice Questions with Answer
Explanations Immunostaining • Antibodies • Tissue
Processing • Quality Control • Diagnostic Pathology •
Laboratory Preparation
SECTION 1: GENERAL IMMUNOLOGY (Questions 1–15)
Question 1. Which of the following BEST describes the difference between a
monoclonal and a polyclonal antibody?
A) Monoclonal antibodies are produced by multiple B-cell clones, while
polyclonal antibodies are produced by a single B-cell clone
B) Monoclonal antibodies are produced by a single B-cell clone and recognize
a single epitope, while polyclonal antibodies are produced by multiple B-cell
clones and recognize multiple epitopes
C) Monoclonal antibodies are less specific than polyclonal antibodies
D) Polyclonal antibodies are produced in vitro, while monoclonal antibodies are
produced in vivo
E) Monoclonal antibodies are always IgG, while polyclonal antibodies are always
IgM
Rationale: Monoclonal antibodies are produced by a single B-cell clone and
recognize a single epitope, providing high specificity and consistency. Polyclonal
antibodies are produced by multiple B-cell clones and recognize multiple epitopes
on the same antigen, offering higher sensitivity but greater batch-to-batch
variability. Monoclonal antibodies are produced by hybridoma technology in vitro,
while polyclonal antibodies are typically produced in vivo (e.g., in rabbits, goats).
Question 2. Which immunoglobulin class is MOST commonly used in
immunohistochemistry?
A) IgA
B) IgM
,C) IgG
D) IgE
E) IgD
Rationale: IgG is the most commonly used immunoglobulin class in
immunohistochemistry due to its high affinity, stability, and ability to penetrate
tissues well. IgM antibodies are larger and less tissue-penetrant. IgA, IgE, and IgD
are rarely used in IHC applications.
Question 3. What is the function of the Fc region of an antibody?
A) Binding to Fc receptors on cells and complement activation
B) Antigen binding
C) Epitope recognition
D) Light chain synthesis
Rationale: The Fc (fragment crystallizable) region of an antibody mediates
binding to Fc receptors on cells (e.g., macrophages, B cells) and activates the
complement system. The Fab (fragment antigen-binding) region contains the
variable domains responsible for antigen binding and epitope recognition. The Fc
region is involved in effector functions but not antigen recognition.
Question 4. What is the purpose of antibody titration in immunohistochemistry?
A) To increase the number of cells stained
B) To determine the optimal antibody concentration that maximizes specific
staining while minimizing background
C) To reduce the cost of antibodies
D) To eliminate the need for antigen retrieval
E) To increase the incubation time
Rationale: Antibody titration determines the optimal concentration of primary
antibody that produces the strongest specific signal with the least background. Too
high a concentration causes nonspecific binding; too low a concentration results in
weak or absent staining. Titration is a critical step in assay optimization.
,Question 5. Which of the following is TRUE about the use of isotype controls in
immunohistochemistry?
A) Isotype controls should always be used in place of positive controls
B) Isotype controls are used to assess nonspecific binding of the primary
antibody to tissue components
C) Isotype controls are required for all IHC assays
D) Isotype controls should be used at a different concentration than the primary
antibody
E) Isotype controls eliminate the need for negative controls
Rationale: Isotype controls use an irrelevant antibody of the same isotype and at
the same concentration as the primary antibody to assess nonspecific binding. They
are not a substitute for positive controls. Isotype controls are recommended but not
always required; their use depends on the assay and regulatory requirements.
Question 6. What is the recommended storage temperature for most unconjugated
primary antibodies?
A) Room temperature
B) 2–8°C (refrigerated)
C) -80°C
D) 37°C
E) Liquid nitrogen
Rationale: Most unconjugated primary antibodies should be stored at 2–8°C
(refrigerated) to maintain stability. Some antibodies may require different storage
conditions, but refrigeration is the standard for most IHC antibodies. Freezing can
damage antibody structure, and room temperature can lead to degradation over
time.
Question 7. Which of the following is a characteristic of a well-validated IHC
antibody?
A) It produces strong staining in all tissues
B) It produces the expected staining pattern in positive tissues and no staining
in negative tissues
C) It produces no background staining regardless of concentration
, D) It is always monoclonal
E) It requires no titration
Rationale: A well-validated IHC antibody produces the expected staining pattern
(correct cellular localization) in tissues known to express the antigen and no
staining in tissues known not to express the antigen. Validation includes testing
positive and negative tissues, confirming specificity, and demonstrating
reproducibility. Antibodies should be titrated for optimal performance.
Question 8. What is the purpose of a positive control in immunohistochemistry?
A) To assess nonspecific binding
B) To verify that the staining procedure and reagents are working correctly
C) To measure background staining
D) To replace negative controls
E) To determine antibody concentration
Rationale: A positive control is a tissue specimen known to express the target
antigen. It verifies that the entire staining procedure (including antigen retrieval,
primary antibody, detection system, and chromogen) is working correctly. If the
positive control fails to stain, the assay run should be repeated.
Question 9. Which of the following is TRUE regarding antibody dilution?
A) Antibodies should always be used undiluted
B) Antibodies should be diluted according to the manufacturer's
recommendations and validated in-house
C) Antibodies can be diluted arbitrarily based on cost
D) Dilution has no effect on staining intensity
E) Dilution is only necessary for polyclonal antibodies
Rationale: Antibodies should be diluted according to the manufacturer's
recommendations and validated in-house to determine the optimal working
dilution. Using an incorrect dilution can result in weak staining (too dilute) or high
background (too concentrated). Cost should not drive dilution decisions without
validation.
Immunohistochemistry Practice Questions with Answer
Explanations Immunostaining • Antibodies • Tissue
Processing • Quality Control • Diagnostic Pathology •
Laboratory Preparation
SECTION 1: GENERAL IMMUNOLOGY (Questions 1–15)
Question 1. Which of the following BEST describes the difference between a
monoclonal and a polyclonal antibody?
A) Monoclonal antibodies are produced by multiple B-cell clones, while
polyclonal antibodies are produced by a single B-cell clone
B) Monoclonal antibodies are produced by a single B-cell clone and recognize
a single epitope, while polyclonal antibodies are produced by multiple B-cell
clones and recognize multiple epitopes
C) Monoclonal antibodies are less specific than polyclonal antibodies
D) Polyclonal antibodies are produced in vitro, while monoclonal antibodies are
produced in vivo
E) Monoclonal antibodies are always IgG, while polyclonal antibodies are always
IgM
Rationale: Monoclonal antibodies are produced by a single B-cell clone and
recognize a single epitope, providing high specificity and consistency. Polyclonal
antibodies are produced by multiple B-cell clones and recognize multiple epitopes
on the same antigen, offering higher sensitivity but greater batch-to-batch
variability. Monoclonal antibodies are produced by hybridoma technology in vitro,
while polyclonal antibodies are typically produced in vivo (e.g., in rabbits, goats).
Question 2. Which immunoglobulin class is MOST commonly used in
immunohistochemistry?
A) IgA
B) IgM
,C) IgG
D) IgE
E) IgD
Rationale: IgG is the most commonly used immunoglobulin class in
immunohistochemistry due to its high affinity, stability, and ability to penetrate
tissues well. IgM antibodies are larger and less tissue-penetrant. IgA, IgE, and IgD
are rarely used in IHC applications.
Question 3. What is the function of the Fc region of an antibody?
A) Binding to Fc receptors on cells and complement activation
B) Antigen binding
C) Epitope recognition
D) Light chain synthesis
Rationale: The Fc (fragment crystallizable) region of an antibody mediates
binding to Fc receptors on cells (e.g., macrophages, B cells) and activates the
complement system. The Fab (fragment antigen-binding) region contains the
variable domains responsible for antigen binding and epitope recognition. The Fc
region is involved in effector functions but not antigen recognition.
Question 4. What is the purpose of antibody titration in immunohistochemistry?
A) To increase the number of cells stained
B) To determine the optimal antibody concentration that maximizes specific
staining while minimizing background
C) To reduce the cost of antibodies
D) To eliminate the need for antigen retrieval
E) To increase the incubation time
Rationale: Antibody titration determines the optimal concentration of primary
antibody that produces the strongest specific signal with the least background. Too
high a concentration causes nonspecific binding; too low a concentration results in
weak or absent staining. Titration is a critical step in assay optimization.
,Question 5. Which of the following is TRUE about the use of isotype controls in
immunohistochemistry?
A) Isotype controls should always be used in place of positive controls
B) Isotype controls are used to assess nonspecific binding of the primary
antibody to tissue components
C) Isotype controls are required for all IHC assays
D) Isotype controls should be used at a different concentration than the primary
antibody
E) Isotype controls eliminate the need for negative controls
Rationale: Isotype controls use an irrelevant antibody of the same isotype and at
the same concentration as the primary antibody to assess nonspecific binding. They
are not a substitute for positive controls. Isotype controls are recommended but not
always required; their use depends on the assay and regulatory requirements.
Question 6. What is the recommended storage temperature for most unconjugated
primary antibodies?
A) Room temperature
B) 2–8°C (refrigerated)
C) -80°C
D) 37°C
E) Liquid nitrogen
Rationale: Most unconjugated primary antibodies should be stored at 2–8°C
(refrigerated) to maintain stability. Some antibodies may require different storage
conditions, but refrigeration is the standard for most IHC antibodies. Freezing can
damage antibody structure, and room temperature can lead to degradation over
time.
Question 7. Which of the following is a characteristic of a well-validated IHC
antibody?
A) It produces strong staining in all tissues
B) It produces the expected staining pattern in positive tissues and no staining
in negative tissues
C) It produces no background staining regardless of concentration
, D) It is always monoclonal
E) It requires no titration
Rationale: A well-validated IHC antibody produces the expected staining pattern
(correct cellular localization) in tissues known to express the antigen and no
staining in tissues known not to express the antigen. Validation includes testing
positive and negative tissues, confirming specificity, and demonstrating
reproducibility. Antibodies should be titrated for optimal performance.
Question 8. What is the purpose of a positive control in immunohistochemistry?
A) To assess nonspecific binding
B) To verify that the staining procedure and reagents are working correctly
C) To measure background staining
D) To replace negative controls
E) To determine antibody concentration
Rationale: A positive control is a tissue specimen known to express the target
antigen. It verifies that the entire staining procedure (including antigen retrieval,
primary antibody, detection system, and chromogen) is working correctly. If the
positive control fails to stain, the assay run should be repeated.
Question 9. Which of the following is TRUE regarding antibody dilution?
A) Antibodies should always be used undiluted
B) Antibodies should be diluted according to the manufacturer's
recommendations and validated in-house
C) Antibodies can be diluted arbitrarily based on cost
D) Dilution has no effect on staining intensity
E) Dilution is only necessary for polyclonal antibodies
Rationale: Antibodies should be diluted according to the manufacturer's
recommendations and validated in-house to determine the optimal working
dilution. Using an incorrect dilution can result in weak staining (too dilute) or high
background (too concentrated). Cost should not drive dilution decisions without
validation.
