Amyloid A (
AA) amyloidosis is characterized by the extracellular deposition of AA
amyloid and results in the irreversible dysfunction of parenchymal organs. In experimental models, AA
amyloid deposits are cleared following a decrease in circulating
serum amyloid A (SAA) concentrations. Additional inflammatory stimuli during this recovery process may induce more severe
amyloid redeposition. In the present study, we confirmed the deposition, clearance, and reinduction of AA
amyloid deposits in
interleukin 1 receptor antagonist knockout mice (IL-1raKO) and studied the SAA levels and
amyloid-enhancing factor activity based on the time-dependent changes of
amyloid deposition. Histopathologically, following initial (day 0) injection of
amyloid-enhancing factor in combination with an inflammatory stimulus (
silver nitrate [AgNO3]),
amyloid deposition peaked by day 20, and its deposition gradually decreased after day 35. SAA concentrations in serum were precipitously elevated on day 1 but returned to normal levels by day 10, whereas the SAA dimer was detected in serum after day 45. An additional AgNO3 injection was administered to mice with
amyloidosis on day 5, 10, 35, or 50, and all mice developed large
amyloid deposits.
Amyloid deposition was most severe in mice treated with AgNO3 on day 35. The inoculation of sera from mice with
AA amyloidosis, combined with AgNO3, induced
AA amyloidosis. Serum samples collected on days 35 and 50, which contained high concentrations of the SAA dimer, induced
amyloidosis in a high proportion (83%) of mice. Therefore, increased SAA and/or its dimer in serum during the recovery process may markedly exacerbate the development of
AA amyloidosis.