Phagocytosis of amyloid: In vitro interaction of mouse peritoneal macrophages with human amyloid fibrils and their accelerated uptake after dye binding

Macrophages and pancreatic islet amyloidosis

Islet amyloid formed from islet amyloid polypeptide (IAPP, amylin) is found in spontaneously diabetic monkeys and cats. Islet amyloidosis is progressive, apparently irreversible and is associated with destruction of insulin-secreting cells. The role of macrophages in the destruction and removal of islet amyloid is unknown. Therefore, the presence and morphology of macrophages were determined by electron and quantitative light microscopy in islets of diabetic and nondiabetic man and monkeys and in transgenic mice expressing the gene for human IAPP. Tissue macrophages were present in all pancreatic sections and tissue distribution was similar in exocrine and endocrine areas. There was no difference in macrophage density in amyloidotic and amyloid-free islets in monkeys and man. Macrophage density was similar in islets of transgenic mice expressing human IAPP which do not contain amyloid in vivo but in which fibrils are formed in vitro following islet isolation compared to islets from mice expressing rat IAPP which is not amyloidogenic. IAPP amyloid fibrils were visible by electron microscopy in lysosomes of pancreatic macrophages in man, monkeys and human IAPP transgenic mice. Thus, human IAPP is internalised but inefficiently degraded by tissue macrophages. Diabetes-associated amyloidosis is not associated with visible recruitment of macrophages for removal of amyloid or islet debris.

Ultrastructural evidence for intracellular formation of amyloid fibrils in macrophages

Early amyloid deposition in the spleen was studied by immunoelectron microscopy following the administration of rapid amyloid-inducing agents to mice. Two days after the injection of an amyloid-enhancing factor and casein solution, a small amount of amyloid material was observed at the border of the white pulp and the marginal zone (perifollicular area) and also within the white pulp. At this stage, amyloid fibrils were seen mainly in an extracellular distribution along the cytoplasmic processes of reticular cells and also in the cytoplasmic invaginations of macrophages. By immunoelectron microscopy, gold particles labelled fibrillar structures in lysosome-derived organelles in some macrophages as well as dense bodies consisted of a homogeneous, granular matrix not having any recognizable fibrillar structures. Similar immuno-labelled organelles were also observed in the amyloid resorption stage, although, at that stage, they commonly contained other phagocytized materials as well. From these findings, we suggest that at least some amyloid fibrils are polymerized in the cytoplasm of the macrophages by the proteolytic cleavage of previously pinocytized serum amyloid A protein (SAA).

Amyloidosis of specialized mesodermal tissues in non-myelomatous monoclonal gammopathy. A pathogenetic hypothesis

The follow-up and the pathological findings of a previously described case of non-myelomatous monoclonal gammopathy with relapsing localized amyloid masses of the shoulder joints are reported. The peculiar "mesodermal" distribution of amyloid deposits, strictly limited to tissues lined by mesothelial or endothelial cells emphasizes the role of local factors in the pathogenesis of amyloidosis thus supporting the hypothesis that amyloid deposition can be related also to some differentiated tissues with peculiar local susceptibility. The morphological findings of the present case enable the Authors to suggest a pathogenic mechanism for amyloid deposition.

[The influence of dyes with special affinity to amyloid on the resorption of casein-induced amyloidosis in mice (author's transl)]

1. The influence of dyes with special affinity to amyloid on the resorption of experimental amyloidosis was studied in mice (A/J/Bom). 2. The amyloidosis was produced by injections of 5% casein over a period of seven weeks. After an interval of six weeks the animals received 0.5 ml of a 0.01% dye solution intraperitoneally (congo red, diamine green, Evans blue) or 0.9% NaCl (controls) every seventh day over a period of 22 weeks. 10, 17, and 22 weeks after the dye treatment was started 3-4 animals of each group were sacrificed and studied histologically. 3. In contrast to the in vitro findings of Shirahama et al. (1971), in vivo there is no acceleration of amyloid resorption by congo red. In the same way diamine green does not accelerate the resorption of amyloid. Evans blue produces a decrease in the amount of amyloid, but at the same time it causes wasting in the animals. Moreover, congo red and diamine green produce amyloidosis by themselves. 4. From our findings neither congo red nor the other amyloidaffine dyes studied, diamine green and Evans blue, are suitable for a therapy of amyloidosis.