Parallel intraylysosomal amyloid fibrils, a possible result of phagocytosis.

Vacuoles of mesenchymal cells in the papillae of bovine kidneys with amyloidosis were studied by histochemical electron microscopy for acid phosphatase as a marker for lysosomes. The vacuoles contained parallel amyloid fibrils. The vacuoles of reticular interstitial cells were found to be lysosomes. Vacuoles of macrophage-like cells of the same papillae were positive, partially positive, or negative for the enzyme activity. A suspension of papillary material was injected subcutaneously in rats in a 21-day light and electron microscopy and enzyme histochemistry study. Amyloid was demonstrated in vacuoles of macrophages throughout this period and initially also in neutrophils. In most vacuoles amyloid fibrils were randomly arranged but in others parallel arrangement was demonstrated. Amyloid was only at the inoculation sites. Intralysosomal bovine amyloid may occur in parallel fibrillar arrangement without a definite indication for amyloid production.