Histochemical classification of systemic amyloid fibril proteins. Alkaline guanidine method.

The alkaline guanidine method facilitates differentiation between different types of amyloid fibril proteins in formaldehyde-fixed, paraffin-embedded tissue sections. Systemic AA-type amyloids lost Congophilia (affinity of Congo red) after incubation with alkaline guanidine for one minute. Systemic AL-type amyloids lost or markedly decreased Congophilia after two hours of treatment with alkaline guanidine. Systemic prealbumin-type amyloids were resistant to incubation for two hours. On the other hand, some cerebral amyloid plaques from patients with Creutzfeldt-Jakob disease and Gerstmann-Sträussler syndrome markedly decreased Congophilia, while in other amyloid plaques, Congophilia was not decreased even with two hours of treatment. The senile plaques from those patients with Alzheimer's disease did not diminish Congophilia after alkaline guanidine treatment. Thus, while this method does not differentiate types of cerebral amyloid protein, it does clearly differentiate types of systemic amyloid fibril proteins.