ASCP Immunohistochemistry

Question 1

What is the purpose of antigen retrieval in immunohistochemistry (IHC)?

Accepted Answer

To unmask epitopes altered by formalin fixation

Answer

To deparaffinize sections

Answer

To block endogenous peroxidase

Answer

To apply the secondary antibody

Question 2

Which of the following describes the avidin-biotin complex (ABC) method in IHC?

Accepted Answer

Indirect amplification system using avidin-biotin affinity

Answer

Direct antibody-chromogen system

Answer

Enzyme-only detection system

Answer

Fluorescent antibody method

Question 3

Why is endogenous peroxidase activity blocked in IHC protocols using HRP-based detection?

Accepted Answer

To eliminate background staining from naturally occurring peroxidases (e.g., in RBCs)

Answer

To prevent tissue damage

Answer

To improve antigen retrieval

Answer

To prevent antibody aggregation

Question 4

What chromogen is most commonly used with HRP-based IHC and produces a brown reaction product?

Accepted Answer

DAB (3,3'-diaminobenzidine)

Answer

BCIP/NBT (blue)

Answer

AEC (red)

Answer

Fast Red

Question 5

What is a positive control in IHC and why is it required?

Accepted Answer

A tissue known to contain the target antigen, run to confirm the staining protocol works

Answer

A tissue section without primary antibody to check background

Answer

A section stained only with the chromogen

Answer

A tissue treated with buffer instead of antibody

Question 6

Which heat-based antigen retrieval method is most commonly used in routine IHC?

Accepted Answer

Microwave in citrate buffer (pH 6.0) or EDTA buffer (pH 9.0)

Answer

Autoclave in distilled water

Answer

Water bath in ethanol

Answer

Pressure cooker in acetone