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Amyloid Stains
BCIT Histo Notes
| Question | Answer |
|---|---|
| Define Amyloid | waxy starch-like substance = glycoprotein |
| Amyloidosis | variety of diseases in which a protein deposited throughout the body that gradually interferes w function |
| List the 3 properties of amyloid | -amorphous -extracellular -eosinophilic |
| What makes up an amyloid deposit? | largely protein and variable amount of carbohydrates |
| Historically, how was starch detectedf? | empirical test called Lugol's Iodine test - blue/black reaction was positive for the presence of starch - amyloid reacts the same way due in part to its carbohydrate content and complex conformation |
| Describe a beta pleated sheet | this conformation is critical for the pathogenesis of amyloid, anti-parallel beta-pleated sheet held together by H bonds |
| Describe primary amyloidosis | no known cause characterized by localized deposits of amyloid which are found in skeletal, heart and skin tissue |
| Describe secondary amyloidosis | associated w inflammatory diseases like TB, arthritis and depositis are found systemically in liver, spleen, kidney |
| How many unique proteins are associated w amyloid? | over 20 |
| What is the most common method used to demonstrate amyloid? | Alkaline Congo Red stain |
| Describe the Congo Red staining method | non-ionic staining method, staining likely via H bonds |
| What does the Congo Red method rely on in order to stain? | linear dye that fits into the beta pleated sheet conformation |
| What pH is the Congo Red method employed at? | Alkaline pH to encourage H bonding |
| Why is the Congo Red dye solution made up in a saline solution? | any strongly charged tissue component will stain with the dye causing false positives - saline prevents this by quenching opposite charges |
| What substances may cause non-specific binding with Congo Red? | collagen, elastin, cytoplasmic elements |
| How and why is staining w Congo Red easily reveresed? | Dehydration steps can easily reverse staining due to the weak H bonds attaching the dye to the amyloid |
| Describe the appearance of a normal positive result | very pale red/pink, not normally intense staining |
| Since Congo Red staining is somewhat nonspecific, what method is used to improve the specificity? | examination of sections under polarized microscope - Congo Red stained amyloid is birefringent and will appears as bright apple green against dark background due to beta pleated sheet |
| How else can amyloid be demonstrated besides Congo Red stain? | due to content of carbohydrates - PAS, Alcian Blue, Crystal Violet but these are not specific and other carbohydrates are likely to stain |
Created by:
kenziebarroso