Primary local orbital amyloidosis: biochemical identification of the immunoglobulin light chain kappaIII subtype in a small formalin fixed, paraffin wax embedded tissue sample

Abstract

Background: Amyloidosis refers to a heterogeneous group of disorders associated with the deposition of chemically distinct amyloid fibril proteins. Precise determination of chemical amyloid type has diagnostic, therapeutic, and prognostic relevance. Although immunohistochemical techniques are used routinely to determine the amyloid type, the results can be negative or inconclusive, so that biochemical characterisation is often required. The development and application of new biochemical microtechniques suitable for examination of extremely small tissue samples is essential for precise identification of the deposited amyloid proteins.

Aims: To investigate biochemically the amyloid proteins present in a formalin fixed paraffin wax embedded orbital tissue from a patient with localised orbital amyloidosis in whom immunohistochemistry was not helpful in the determination of amyloid type.

Methods: Extraction of amyloid proteins from fixed tissue and their identification was carried out by a recently developed microtechnique. An extremely small tissue sample was dewaxed and extracted with formic acid. The extracted material was analysed using electrophoresis, western blotting, and amino acid sequencing.

Results: Biochemical examination of the extracted proteins showed the presence of immunoglobulin (Ig) derived amyloid proteins, which were composed of the N-terminal fragments of the Ig light chain kappaIII subtype (AL-kappaIII) (16, 8, and 3 kDa).

Conclusions: This is the first chemically proved AL case reported in association with primary localised orbital amyloidosis. The biochemical microtechnique used was useful in achieving a precise diagnosis of amyloid disease, in a case where the results of routine immunohistochemical examination of amyloid were inconclusive.

Figure 1

Haematoxylin and eosin stained section (original magnification, ×200) of the orbital tumour tissue specimen showing deposits of amorphous pink material of amyloid with lymphocytes and foreign body multinucleated giant cells.

Figure 2

Electrophoretic and amino acid sequence analyses of amyloid proteins recovered from the formalin fixed, paraffin wax embedded orbital tissue. Proteins were transferred to a PVDF membrane and stained with Coomassie blue. The excised bands were subjected to N-terminal amino acid sequence analysis. Amino acids are indicated by the single letter code. Lane 1, molecular weight markers; lanes 2 and 3, tissue extracts.

Figure 3

Western blot analysis of amyloid proteins extracted from the formalin fixed, paraffin wax embedded orbital tissue. Proteins were immunostained using antibodies to (A) κ and (B) λ immunoglobulin light chains.