Congo red staining for amyloid under polarized light shows: September 2007
Ans. D: Green birefringenceThe traditional way of identifying amyloid in tissue sections has been staining with Congo red and demonstration of green birefringence under crossed polarizers.The original method of Congo red staining was described by Bennhold in 1922.The most common modification in the above technique is the alkaline Congo red method described by Puchtler and coworkers in 1962.Specificity is improved by using freshly prepared stain and a staining solution fully saturated with sodium chloride. Amyloid proteins can be fuher distinguished by autoclaving or by treating the tissue with potassium permanganate or alkaline guanidine.Other methods of detection of amyloid include fluorescent stains, e.g., thioflavin T or S, and metachromatic stains such as crystal violet.Immunofluorescence and immunoperoxidase methods are used to identify and classify amyloid proteins in tissues. Antibodies against the P component, proteins AA and AL and FAP have been used with great precision.Due to cross-reactivity, these methods do not differentiate between some types of familial and senile systemic amyloidosis
Silver birefringence
Golden birefringence
Blue birefringence
Green birefringence