HTL Immunohistochemistry & Special Stains 1 — Questions and Answers
Question 1: What is the primary purpose of immunohistochemistry (IHC) in histotechnology?
- To stain the entire tissue section
- To detect specific proteins and antigens in tissue (Correct answer)
- To remove pathogens from tissue
- To measure tissue thickness
Correct answer: To detect specific proteins and antigens in tissue
Immunohistochemistry (IHC) is a powerful technique that utilizes the specific binding of antibodies to antigens (proteins) within tissue sections. This allows histotechnologists and pathologists to precisely localize and identify specific cellular markers, pathogens, or disease-associated proteins. IHC is invaluable for diagnosis, prognosis, and therapeutic guidance, especially in oncology, by revealing the presence and distribution of target molecules.
Question 2: What is the primary advantage of using special stains in histology?
- To stain all tissue components equally
- To selectively stain specific tissue components for better visualization (Correct answer)
- To eliminate the need for tissue preservation
- To increase tissue sample size
Correct answer: To selectively stain specific tissue components for better visualization
The primary advantage of using special stains in histology is their ability to selectively target and highlight particular cellular or extracellular components that are not adequately visualized by routine H&E staining. By selectively staining specific structures like collagen, elastic fibers, mucin, lipids, or microorganisms, these stains provide crucial diagnostic information that helps pathologists identify and characterize various diseases more precisely.
Question 3: What is the most commonly used marker in immunohistochemistry?
- Dye-based stains
- Antibodies that bind to specific antigens (Correct answer)
- Fluorescent dyes
- Enzyme-based markers
Correct answer: Antibodies that bind to specific antigens
Immunohistochemistry (IHC) relies on the highly specific binding of antibodies to target antigens within tissue samples. These antibodies are typically labeled (e.g., with enzymes or fluorochromes) to visualize the location and expression of the specific antigen, making them the fundamental marker for detection. They provide the specificity needed to identify particular cellular components.
Question 4: How does the biotin-avidin system function in immunohistochemistry?
- It reduces antibody binding
- It enhances signal detection by binding biotin-labeled antibodies (Correct answer)
- It stains all cell components
- It is used to fix tissue samples
Correct answer: It enhances signal detection by binding biotin-labeled antibodies
The biotin-avidin (or streptavidin) system is a common amplification strategy in immunohistochemistry. Biotin is conjugated to a secondary antibody, and avidin (or streptavidin) is then used, which has a very high affinity for biotin. This avidin is typically conjugated to an enzyme, allowing for multiple enzyme molecules to bind to each biotinylated antibody, thereby significantly enhancing the signal and improving detection sensitivity.
Question 5: What type of tissue components are best highlighted using periodic acid-Schiff (PAS) stain?
- Proteins
- Carbohydrates and glycoproteins (Correct answer)
- Nucleic acids
- Lipids
Correct answer: Carbohydrates and glycoproteins
The Periodic Acid-Schiff (PAS) stain is a histochemical technique specifically designed to detect carbohydrates and carbohydrate-rich macromolecules. Periodic acid oxidizes vicinal diols in carbohydrates to aldehydes, which then react with Schiff's reagent to produce a distinctive magenta color. This makes it ideal for highlighting structures like glycogen, mucins, and basement membranes in tissue sections.
Question 6: How does the use of DAB (diaminobenzidine) contribute to immunohistochemistry?
- It enhances the color of the tissue
- It produces a brown color at the site of antibody binding (Correct answer)
- It stains the nucleus blue
- It highlights lipids
Correct answer: It produces a brown color at the site of antibody binding
Diaminobenzidine (DAB) is a chromogen commonly used in enzyme-linked immunohistochemistry, particularly with horseradish peroxidase (HRP). When HRP acts on DAB in the presence of hydrogen peroxide, it oxidizes DAB to form an insoluble, dark brown precipitate. This brown color precisely marks the location where the antibody has bound to its target antigen, allowing for microscopic visualization.
Question 7: Why is it important to use a positive control in immunohistochemistry?
- To increase the sensitivity of the assay
- To confirm the antibody binding is functional and reliable (Correct answer)
- To reduce tissue sample preparation time
- To enhance the color intensity of the tissue
Correct answer: To confirm the antibody binding is functional and reliable
A positive control in immunohistochemistry is a tissue sample known to express the target antigen, which should yield a positive staining result. Its inclusion confirms that the antibody is binding correctly, the detection system is working, and the overall staining procedure is effective. This ensures the reliability of both positive and negative results and validates the assay's performance.
Question 8: What is the purpose of using immunofluorescence in histology?
- To use antibodies as fluorescent markers
- To enhance the resolution of tissue samples
- To identify specific proteins or antigens in tissue (Correct answer)
- To stain the entire tissue sample
Correct answer: To identify specific proteins or antigens in tissue
Immunofluorescence (IF) is a powerful technique in histology that uses antibodies conjugated with fluorescent dyes to detect and visualize specific antigens (proteins) within tissue sections or cells. When excited by light of a specific wavelength, the fluorescent dye emits light, allowing researchers to precisely locate and identify the target molecules under a fluorescence microscope. This method is crucial for studying protein localization and expression patterns.
Question 9: How does immunohistochemistry contribute to cancer diagnosis?
- By providing information about tissue structure
- By detecting cancerous markers and identifying cancer types (Correct answer)
- By monitoring tumor size
- By increasing the accuracy of imaging techniques
Correct answer: By detecting cancerous markers and identifying cancer types
Immunohistochemistry (IHC) is invaluable in cancer diagnosis as it allows pathologists to identify specific protein markers (antigens) expressed by cancer cells. This helps in classifying tumor types, determining their origin, assessing prognosis, and guiding treatment decisions. IHC provides crucial molecular information that complements basic tissue morphology, leading to more precise diagnoses and personalized patient care.
HTL Immunohistochemistry & Special Stains 1
What is the primary purpose of immunohistochemistry (IHC) in histotechnology?