In surgical pathology, correct immunohistochemical identification of
AL amyloidosis poses a particular problem. Immunostaining for lambda- or kappa-light chains is commonly encountered even in non-
immunoglobulin-derived
amyloidoses, which leads to a false-positive classification as
AL amyloidosis. In this respect, microextraction of
amyloid proteins from surgical pathology specimens and their subsequent biochemical characterization may prove useful in reaching the correct diagnosis. In this study, we investigated systematically the influence of fixation on the extraction of
amyloid proteins from
amyloid-containing tissue samples. Tissue samples were obtained from a patient with generalized
AA amyloidosis and from a second patient with generalized
AL amyloidosis. The samples were stored either unfixed or fixed in
phosphate buffered 4% p-
formaldehyde,
methacarn, or Bouin for 3 days, 1 week, or 1 month. Thereafter,
proteins were extracted according to the procedure of Layfield et al, separated by SDS-PAGE and subjected to Western blotting, using
antibodies directed against AA
amyloid and
immunoglobulin-derived lambda-light chain. Following this procedure, a variety of differently sized AA
amyloid or lambda-light chain immunoreactive
protein bands were found in both patients, which is typical for
amyloid proteins. Fixation time did not per se prohibit the extraction of these
amyloid proteins from tissue samples, which remained detectable irrespective of fixation time. Although all three
fixatives impaired the resolution of some, but not all, individual
amyloid proteins, this procedure may help to confirm or reject a diagnosis of
AL amyloidosis, because detection of several lambda- or kappa-light chain immunoreactive
protein bands in the low-molecular-weight range (<20 kDa) is a common characteristic of their
amyloid nature.