Immunohistochemistry & Special Stains Flashcards

Which special stain is used to demonstrate reticulin fibers in tissue, particularly in liver and bone marrow biopsies?

Answer: Gordon and Sweet's silver impregnation (reticulin stain)

Gordon and Sweet's silver impregnation stains reticulin (type III collagen) fibers black, essential for evaluating fibrosis in liver and marrow.

Tyramide signal amplification (TSA) in IHC is used primarily when:

Answer: The antigen is scarce or antibody affinity is low, requiring enhanced sensitivity

TSA deposits large amounts of tyramide-hapten at HRP sites, dramatically amplifying signal for low-abundance antigens.

Which IHC marker is positive in both Schwann cells and melanoma, making it useful but non-specific in differential diagnosis?

Answer: S100 protein

S100 is expressed in Schwann cells, melanocytes, Langerhans cells, and many other cell types, limiting its specificity despite high sensitivity for melanoma.

The Oil Red O stain must be performed on which type of tissue section, and why?

Answer: Frozen sections, because lipids are dissolved by paraffin processing solvents

Lipids are dissolved by the alcohols and xylene used in routine paraffin processing, so Oil Red O must be performed on frozen sections.

In multiplex IHC/IF, which approach allows simultaneous detection of multiple antigens on the same tissue section?

Answer: Applying all primary antibodies from different species with species-specific secondaries or using tyramide cycling

Multiplex IHC uses species-specific secondaries for different primaries, or cyclic tyramide-based platforms to sequentially deposit distinguishable reporters for multiple antigens.

Which stain is used to demonstrate mast cell granules, staining them metachromatically purple-red against a blue background?

Answer: Giemsa or toluidine blue

Mast cell granules contain sulfated proteoglycans that stain metachromatically with thiazine dyes like toluidine blue and Giemsa.

PD-L1 IHC scoring for immunotherapy eligibility uses Tumor Proportion Score (TPS) in some cancers and Combined Positive Score (CPS) in others. CPS counts which cells?

Answer: Tumor cells plus PD-L1-positive immune cells, divided by total viable tumor cells × 100

CPS = (number of PD-L1 positive tumor cells + lymphocytes + macrophages) / total viable tumor cells × 100, and is used for gastric/GEJ and cervical cancers.