An analysis of the close relationship of lysosomes to early deposits of amyloid. Ultrastructural evidence in experimental mouse amyloidosis.

On the basis of recent morpholgic and biochemical studies which suggested the possible involvement of reticuloendothelial (RE) cells and proteolytic enzymes in amyloidogenesis, the present study was undertaken to examine the ultrastructural interrelationship between lysosomes and amyloid fibrils at the sites of very early amyloid deposition. In the spleen, liver and kidney of the experimental mouse model, foci of amyloid deposits were closely associated with the RE cells. The lysosomal enzyme activity, as marked by cytochemical demonstration of acid glycerophosphatase activity, was localized in the primary type lysosomes (as defined by their electron microscopic appearance), in the Golgi complexes, in the small cytoplasmic vesicles and occasionally widespread in the cytoplasm. They showed an intimate relationship to the amyloid fibrils. The findings were interpreted as favoring the hypothesis that the hydrolases play a role in amyloid fibril formation. The enzyme activity was also demonstrated in the secondary type lysosomes which occasionally contained amyloid fibrils that appeared to be phagocytized.