Generation and use of site-specific antibodies to serum amyloid A for probing amyloid A development

Serum amyloid A (SAA) is an acute phase reactant and the putative precursor of an amyloid fibril protein (AA). During amyloidogenesis in mice, the C-terminal portion of SAA that consists of 28 amino acids is cleaved off to produce the 75 amino acid AA. Of three known isotypes of SAA, SAA2 has been identified as amyloidogenic. For differential immunologic recognition of SAA and AA, antisera were generated in rabbits against AA protein and a synthetic peptide corresponding to the C-terminal (amino acids 84 to 103) of murine SAA2. The anti-AA antiserum reacted with AA and SAA, but the anti-peptide antiserum reacted with SAA only. Immunohistochemically anti-peptide antiserum predominantly stained the rims of murine amyloid deposits. In contrast, anti-AA antiserum generated an overall homogeneous staining of amyloid deposits. The data lend support to a view that SAA are concentrated in the vicinity of the surrounding cells (mostly macrophages) where they are processed to AA, or that SAA are deposited initially as components of the amyloid fibrils onto the outside margin of amyloid deposits and the C-terminus is cleaved off as maturation of the amyloid fibril progresses.