Immunoglobulin derived depositions in the nervous system: novel mass spectrometry application for protein characterization in formalin-fixed tissues

Abstract

Proteinaceous deposits are occasionally encountered in surgically obtained biopsies of the nervous system. Some of these are amyloidomas, although the precise nature of other cases remains uncertain. We studied 13 cases of proteinaceous aggregates in clinical specimens of the nervous system. Proteins contained within laser microdissected areas of interest were identified from tryptic peptide sequences by liquid chromatography-electrospray tandem mass spectrometry (LC-MS/MS). Immunohistochemical studies for immunoglobulin heavy and light chains and amyloidogenic proteins were performed in all cases. Histologically, the cases were classified into three groups: 'proteinaceous deposit not otherwise specified' (PDNOS) (n ¼ 6), amyloidoma (n ¼ 5), or 'intracellular crystals' (n ¼ 2). LC-MS/MS demonstrated the presence of l, but not k, light chain as well as serum amyloid P in all amyloidomas. l-Light-chain immunostaining was noted in amyloid (n ¼ 5), although demonstrable monotypic lymphoplasmacytic cells were seen in only one case. Conversely, in PDNOS k, but not l, was evident in five cases, both light chains being present in a single case. In three cases of PDNOS, a low-grade B-cell lymphoma consistent with marginal zone lymphoma was present in the brain specimen (n ¼ 2) or spleen (n ¼ 1). Lastly, in the 'intracellular crystals' group, the crystals were present within CD68 þ macrophages in one case wherein k-light chain was found by LC-MS/MS only; the pathology was consistent with crystalstoring histiocytosis. In the second case, the crystals contained immunoglobulin G within CD138 þ plasma cells. Our results show that proteinaceous deposits in the nervous system contain immunoglobulin components and LC-MS/MS accurately identifies the content of these deposits in clinical biopsy specimens. LC-MS/MS represents a novel application for characterization of these deposits and is of diagnostic utility in addition to standard immunohistochemical analyses.

Amyloidosis of the breast: predominantly AL type and over half have concurrent breast hematologic disorders

“…More recently, the technique of laser microdissection mass spectrometry-based proteomics was introduced as a powerful tool for the diagnosis and typing of amyloidosis with high sensitivity and specificity. [14][15][16] It is particularly helpful in diagnosing some of the rare forms of amyloidosis, such as fibrinogen A a-chain, apolipoprotein AI, apolipoprotein AII, ALECT2, AH and AH/AL, which may not be diagnosed by immunohistochemistry. One of the most practical aspects of the technique of mass spectrometry-based proteomics for amyloid typing is that it is done on formalin-fixed paraffin-embedded tissue instead of requiring fresh, frozen or other specially stored tissue samples.…”

“…The methods for mass spectrometry-based proteomics in our center have previously been published. [14][15][16] Briefly, for each case, 10 mm-thick sections of formalin-fixed paraffinembedded tissues were stained with Congo red. The Congo red deposits were identified under fluorescence light and laser microdissected.…”

Classification of amyloidosis by laser microdissection and mass spectrometry–based proteomic analysis in clinical biopsy specimens

“…The methods have been published previously, 18 and the details are provided in the supplemental Methods. In brief, for each case, a 10-m paraffin section was stained with CR, and then amyloid deposits were identified under fluorescent light and microdissected with LMD (supplemental Video 1).…”

Guidelines on the diagnosis and investigation of AL amyloidosis

“…Hereditary fibrinogen A a-chain amyloidosis should be considered in any patient with an exclusively renal presentation and has a distinctive appearance on renal biopsy with extensive glomerular involvement in the absence of significant extra-glomerular amyloid. DNA analysis is available (Rodriguez et al 2008, Vrana et al 2009) and laser microdissection with mass spectrometry together enable precise identification of amyloid type in most cases (Vrana et al, 2009). Multidimensional Protein Identification Technology (2-dimensional chromatography coupled to tandem mass spectrometry) may also enable amyloid fibril typing from fat aspirate samples (Brambilla et al, 2012).…”