Histological study of experimental murine AA amyloidosis

The localization of amyloid fibril components and the cells related to the formation and resorption of the fibrils are still controversial. We conducted a time-kinetic study to analyse the process of amyloid fibril deposition in the spleen of an AA amyloidosis animal model immunohistochemically. Murine AA amyloidosis was induced by an emulsion injection composed of Freund's complete adjuvant and Mycobacterium butyricum. The serum amyloid A level was the highest at 3 days after the induction and gradually decreased. The amyloid deposition was first detected in extracellular spaces in the marginal zone of the spleen at 7 days after induction. F4/80 positive red pulp macrophages increased in number after the induction and accumulated near the amyloid deposition areas. Amyloid P component (APC) and chondroitin sulphate proteoglycan (CSPG), which are composed of amyloid fibril, were detected in the cytoplasm of F4/80 positive red pulp macrophages and ER-TR9 positive marginal zone macrophages, respectively, then localized in the amyloid deposition areas. APC was also localized in CSPG positive and F4/80 negative cells, which might be fibroblasts at 3 days. These results suggest a close association of APC positive/ER-TR9 positive macrophages and APC positive/CSPG positive fibroblasts in the formation of amyloid fibrils and F4/80 positive macrophages with the resorption of fibrils.