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We set up a laser nephelometric assay for the quantitation of serum amyloid A (SAA) in human plasma. Therefore monospecific antibodies were raised in sheep and used in parallel to measure SAA concentrations by nephelometry and also by radial immunodiffusion, an assay usually applied for determination of SAA. The nephelometric method is precise, simple and unlike radial immunodiffusion results are obtained within an hour. The antigen concentrations determined both by laser nephelometry and radial immunodiffusion correlated highly (r = 0.98). As plasma SAA concentrations were reported to be a possible marker of kidney allograft rejection, the assay was applied to measure SAA concentrations in patients after kidney transplantation. Data were compared with clinical and other biochemical parameters. The period after kidney transplantation is reported for two cases, where SAA plasma concentrations were helpful in diagnosing allograft rejection. The rapid availability of the SAA plasma concentrations by nephelometry makes them a possible additional tool to decide quickly upon antirejection therapy.

On isoelectric focusing of human plasma and subsequent immunoblotting, using antii-human serum amyloid A (SAA) antibodies, a genetic variant of SAA was detected in a family of Turkish origin. All affected members of the family were apparent heterozygotes for the mutant protein, which underwent a charge shift of about one charge unit toward the anode. The variant is likely to be a mutant of the most prominent forms of SAA (SAA1 and SAA2, or SAA1 and SAA1 des Arg). The appearance of a genetic variant of two of the six reported SAA-isoforms in human plasma supports the concept of SAA proteins being products of different genes.

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