Immunohistochemistry & Special Stains Flashcards

What is the primary purpose of immunohistochemistry (IHC) in histotechnology?

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.

What is the primary advantage of using special stains in histology?

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.

What is the most commonly used marker in immunohistochemistry?

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.

How does the biotin-avidin system function in immunohistochemistry?

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.

What type of tissue components are best highlighted using periodic acid-Schiff (PAS) stain?

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.

How does the use of DAB (diaminobenzidine) contribute to immunohistochemistry?

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.

Why is it important to use a positive control in immunohistochemistry?

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.

What is the purpose of using immunofluorescence in histology?

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.

How does immunohistochemistry contribute to cancer diagnosis?

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.