, including the presence of particular genes. It is not a single substance and there is no single cause for it, but a common thread is that the protein in amyloid is a β-pleated sheet instead of the more usual α-helix. The subject may be investigated by internet searches on the subjects of amyloid, amyloidosis, and the individual amyloid types in the list below. The reader is encouraged to do so as it is a large and quite complicated subject. There is a modern overview at Medscape.
The names of the types of amyloid usually start with the letter "A". The following list of the most common types was made by blending the two lists in the Wikipedia articles referenced below and adding some links. The list is not exhaustive.
|Abbreviation||Amyloid type / gene||Description|
|AL||amyloid light chain||AL amyloidosis / multiple myeloma. Contains immunoglobulin light-chains (λ,κ) derived from plasma cells.|
|AA||SAA||AA amyloidosis, rheumatoid arthritis|
|Aβ||β amyloid / APP||Found in Alzheimer disease brain lesions.|
|Aβ2M||β2 microglobulin||Haemodialysis-associated amyloidosis.|
|ATTR||transthyretin / TTR||Familial amyloid polyneuropathies, senile systemic amyloidosis, leptomeningeal amyloidosis.|
|AIAPP||amylin / IAPP||Pancreatic amyloid in type 2 diabetes.|
|AGel||Gelsolin, GSN||Finnish type amyloidosis.|
|AApoA1||APOA1||Familial visceral amyloidosis, atherosclerosis.|
|AFib||FGA||Familial visceral amyloidosis.|
|ALys||LYZ||Familial visceral amyloidosis.|
|ABri||ITM2B||Cerebral amyloid angiopathy, British-type|
||ITM2B||Cerebral amyloid angiopathy, Danish-type.|
|ACys||CST3||Cerebral amyloid angiopathy, Icelandic-type.|
|AKer||Keratoepithelin||Lattice corneal dystrophy.|
|ACal||Calcitonin||Medullary carcinoma of the thyroid.|
|AANF||atrial natriuretic factor||Senile amyloid of atria of heart, cardiac arrhythmias.|
|AMed||Medin||Aortic medial amyloid.|
|—||OSMR||Primary cutaneous amyloidosis.|
|APrP||Prion protein||Deposits in prion diseases may resemble amyloid, i.e. in Creutzfeldt-Jakob disease, Kuru, BSE, and scrapie.|
From a histological perspective the classification is a lot simpler, since the commonly used methods can only show the presence of amyloid in general rather than selectively colour individual types. For the limited differentiations possible between the various types it is necessary to block their staining reaction and compare the staining to an unblocked stained section. The possibilities are given in the chart below.
|Autoclave at 120°C for 30 min.||AA no longer stains with congo red.|
|Autoclave at 120°C for 2 hours.||AL no longer stains with congo red.
Pre-albumin related amyloid shows no change.
|Potassium permanganate oxidation.||AA and β2-microglobulin amyloid no longer stain with congo red.|
|Alkaline guanidine for 1 minute.||AA no longer stains with congo red|
|Alkaline guanidine for 2 hours.||AL and systemic senile amyloid no longer stain with congo red.
Familial amyloid protein retains congo red staining
Immunohistochemistry is the most definitive method for classification of amyloid types by identification of their predominant protein. Amyloid fibrils may also be solubilised and identified in solution, although that is outside the scope of StainsFile.
The methods used for demonstrating amyloid are listed below. Of these, the DMAB nitrite test is a histochemical method for tryptophan using p-dimethylaminobenzaldehyde. The metallic impregnations are rarely used. By far, the most common method and something of a standard, if that word can be applied to amyloid staining, is to use the direct cotton dye, congo red, with the green birefringence it usually imparts.
The term direct cotton dye is used in the textile industry to refer to those dyes which can colour cotton without requiring a mordant, i.e. by direct dyeing. They are usually acid dyes. In the Colour Index their functional name is "direct + colour + number". Some direct cotton dyes are suitable for staining amyloid, notably congo red (direct red 28) and sirius red F3B (direct red 80). Other direct cotton dyes, such as benzo scarlet 4BNS, sold und