Amyloid A (AA) fibril formation in renal tubules occurs intracytoplasmically, possibly at the site of membrane assembling structures

Abstract

Immunoelectron microscopy with anti-AA antibodies was used to study casein induced renal amyloidosis in mice. Amyloid deposits were distributed mainly in the peritubular or perivascular interstitium of the outer zone of the medulla and papillary tip, and to a lesser degree in the inner zone of the medulla, cortex and glomeruli.

Invaginated pits from the basal cytoplasmic membrane of collecting tubules, thin segments of Henle's loop and proximal tubules reacted with anti-AA antibodies. The part of the membrane of cytoplasmic vesicles that contained amyloid fibrils was patchily stained in the thin segment of Henle 's loop. Curious anti-AA positive membrane assembling structures (MAS), which were composed of twisted membranes, filaments or elongated vesicles, were detected in the cytoplasm of the proximal and collecting tubules. These MAS were associated with the pits of the plasma membrane and were undetectable by conventional electron microscopy. In the interstitial capillaries, endothelial pits facing the exterior contained bundles of amyloid fibrils.

The findings suggest that tubular epithelia and interstitial endothelia play a role in amyloidfibrillogenesis in the kidney. In the tubular cytoplasm, reabsorbed SAA appears to form MAS which fuse with the basal plasma membrane and presumably then release complete amyloid fibrils extracellularly. Thus, amyloid fibrillogenesis may take place on the intracytoplasmic membranes in renal tubules.

Key Words:

• AMYLOIDOSIS
• SERUMAMIXOIDA
• IMMUNOHISTOCHEMISTRY
• RENAL TUBULES
• ENDOCYTOSIS
• INFLAMMATION
• LYSOSOME