Selective differentiation between amyloid and connective tissue structures based on the collagen specific topo-optical staining reaction with congo red.

Abstract

There are some difficulties inherent in the identification of amyloid by Congo red anisotropy in the polarisation microscope, mainly because of the possibility of a nonspecific reaction of collageneous structures. The newly recognized collagen-specific Congo red topooptical staining reaction provides a theoretically well-founded possibility for differentiating between amyloid and collagen. In Canada balsam, or other apolar mounting media the Congo red anisotropy of amyloid as well as that of collagen are of the same (additive) optical sign. In gum arabic however they are of opposite signs, additive for amyloid and inversive for collagen. That difference enables a definite differentiation between amyloid and collagen, since in gum arabic Congo red stained amyloid is positively birefringent, and collagen is isotropic or weakly negatively birefringent. Pretreatment of the tissue sections with proteolytic enzymes resulted in a decrease in the general background staining of the tissues as well as in an increase of the inversive Congo red staining reaction of collagen and of the additive reaction of amyloid, providing thereby the possibility of differentiating sensitively and selectively between amyloid and collagen by Congo red anisotropy. Enzymatic removal of the elastic fibers prior to Congo red staining facilitated the exact localisation of senile amyloid deposits in the aortic wall. The initial amyloid deposits were visualized in the smooth muscle cells of the aortic wall. This finding may lead to a new approach to the pathogenesis of senile aortic amyloid.