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Intraperitoneal amyloid formation by amyloid enhancing factor--rich macrophages in ascitic fluid
1Department of Pathology, Hamamatsu University School of Medicine, Japan.
Abstract:
Although resident peritoneal cells from amyloidotic mice (amyloidotic peritoneal cells) are capable of processing the precursor protein of secondary amyloidosis, serum amyloid A (SAA) to amyloid fibrils, the peritoneum is a rare site for amyloid deposition. This is considered to be due to a deficiency of SAA in the peritoneum. To increase the supply of SAA to the peritoneum, ascitic fluid containing about the same protein constituents as in the serum was induced in mice. Amyloidotic peritoneal cells were packed in a microchamber which was shielded with filter membranes, and cultured in ascitic fluid supplemented with additional inflammatory factors. On the 7th day, Congo red-positive structures which showed green birefringence under polarized light were found inside and occasionally outside the chamber. By anti-AA or -SAA immunostaining, amyloid deposits and the cell surfaces of macrophages were positive. Immunologic depletion of T- and B-lymphocytes from the amyloidotic peritoneal cells did not adversely effect the amyloid formation in microchambers. These results suggest that either ascitic fluid containing sufficient amounts of SAA, or peritoneal macrophages with a high amyloid enhancing factor (AEF) activity are indispensable for AA amyloid fibrillogenesis in the peritoneum.
Insights
Peritoneal macrophages can form amyloid fibrils when supplied with sufficient serum amyloid A (SAA) via ascitic fluid. This suggests SAA availability is key for peritoneal amyloid deposition, even without lymphocytes.
Area of Science:
- Immunology
- Pathology
- Biochemistry
Background:
- Secondary amyloidosis involves serum amyloid A (SAA) protein misfolding into amyloid fibrils.
- The peritoneum rarely develops amyloid deposits despite resident cells' amyloidogenic potential.
- Peritoneal SAA deficiency is hypothesized to limit amyloid formation in this site.
Purpose of the Study:
- To investigate the conditions necessary for AA amyloid fibril formation in the peritoneum.
- To determine the role of SAA availability and peritoneal macrophages in AA amyloidogenesis.
Main Methods:
- Amyloidotic peritoneal cells were cultured in a microchamber system using induced ascitic fluid.
- Ascitic fluid was supplemented with inflammatory factors to increase SAA supply.
- Amyloid formation was assessed using Congo red staining and polarized light microscopy.
- Immunostaining for AA and SAA, and lymphocyte depletion were performed.
Main Results:
- Congo red-positive amyloid structures formed within 7 days in microchambers.
- Amyloid deposits and macrophage surfaces showed positive staining for AA and SAA.
- Lymphocyte depletion did not inhibit amyloid formation, implicating macrophages.
Conclusions:
- Sufficient SAA levels in the peritoneum, facilitated by ascitic fluid, are crucial for AA amyloid fibrillogenesis.
- Peritoneal macrophages with high amyloid enhancing factor (AEF) activity are essential for this process.
- Lymphocytes are not required for peritoneal AA amyloid formation under these conditions.