Paper I
Question
Properties of amyloid.
Answer
Physical/structural properties
- Amorphous, eosinophilic, extracellular proteinaceous material on light microscopy (H&E stain)
- Composed of non-branching fibrils, arranged in an antiparallel beta-pleated sheet configuration on X-ray crystallography/electron microscopy — this fibrillar beta-sheet structure underlies all forms of amyloid regardless of the precursor protein
- Insoluble and resistant to proteolytic degradation
Staining properties
- Congo red stain shows characteristic apple-green birefringence under polarized light — the classic diagnostic staining property
- Metachromatic staining with crystal violet/methyl violet (pink-violet colour)
- Fluoresces with Thioflavin T/S under ultraviolet light
Biochemical composition
- Composed of a variable fibrillar protein component specific to the type of amyloidosis (e.g., AL — immunoglobulin light chains; AA — serum amyloid A protein; transthyretin in familial/senile amyloidosis) plus a non-fibrillar component (serum amyloid P component, present in all types)