Immunohistochemistry & Special Stains Flashcards

Congo red staining of amyloid, when viewed under polarized light, produces which characteristic appearance?

Answer: Apple-green birefringence

Amyloid stained with Congo red exhibits apple-green birefringence under polarized light due to its beta-pleated sheet configuration.

Which enzyme is used in the enzymatic antigen retrieval method to unmask antigens in formalin-fixed tissue?

Answer: Protease K or pepsin

Proteinase K or pepsin digest protein cross-links formed during formalin fixation to unmask antigenic sites.

The Warthin-Starry stain is used to demonstrate which organisms in tissue?

Answer: Helicobacter pylori and spirochetes

Warthin-Starry silver impregnation stains spirochetes (including Treponema pallidum) and Helicobacter pylori black against a yellow-brown background.

In IHC, DAB (3,3'-diaminobenzidine) chromogen produces which color at the site of peroxidase activity?

Answer: Brown

DAB is oxidized by horseradish peroxidase to produce an insoluble brown precipitate at the antigen site.

Which IHC panel best differentiates mesothelioma (CK5/6+, calretinin+) from lung adenocarcinoma (TTF-1+, napsin A+)?

Answer: CK5/6, calretinin, TTF-1, napsin A

CK5/6 and calretinin support mesothelioma, while TTF-1 and napsin A support lung adenocarcinoma, making this the standard differentiating panel.

Alcian blue at pH 2.5 stains which type of mucin?

Answer: Sulfated and carboxylated acid mucins

Alcian blue at pH 2.5 stains both sulfated and carboxylated (sialylated) acid mucins blue, while neutral mucins require PAS.

Which fixative artifact can cause strong false-positive nuclear staining with proliferation markers like Ki-67?

Answer: Cold ischemia time over 6 hours

Prolonged cold ischemia time before fixation can cause autolysis and non-specific antibody binding, leading to false-positive nuclear staining.