PrP immunohistochemistry: different protocols, including a procedure for long formalin fixation, and a proposed schematic classification for deposits in sporadic Creutzfeldt-Jakob disease

Accuracy of diagnosis criteria in patients with suspected diagnosis of sporadic Creutzfeldt-Jakob disease and detection of 14-3-3 protein, France, 1992 to 2009

Diagnostic criteria of Creutzfeldt–Jakob disease (CJD), a rare and fatal transmissible nervous system disease with public health implications, are determined by clinical data, electroencephalogram (EEG), detection of 14-3-3 protein in cerebrospinal fluid (CSF), brain magnetic resonance imaging and prion protein gene examination. The specificity of protein 14-3-3 has been questioned. We reviewed data from 1,572 autopsied patients collected over an 18-year period (1992–2009) and assessed whether and how 14-3-3 detection impacted the diagnosis of sporadic CJD in France, and whether this led to the misdiagnosis of treatable disorders. 14-3-3 detection was introduced into diagnostic criteria for CJD in 1998. Diagnostic accuracy decreased from 92% for the 1992–1997 period to 85% for the 1998–2009 period. This was associated with positive detections of 14-3-3 in cases with negative EEG and alternative diagnosis at autopsy. Potentially treatable diseases were found in 163 patients (10.5%). This study confirms the usefulness of the recent modification of diagnosis criteria by the addition of the results of CSF real-time quaking-induced conversion, a method based on prion seed-induced misfolding and aggregation of recombinant prion protein substrate that has proven to be a highly specific test for diagnosis of sporadic CJD.

Antigen retrieval using sodium hydroxide for prion immunohistochemistry in bovine spongiform encephalopathy and scrapie

Formalin-fixed and paraffin wax-embedded (FFPE) tissue sections are usually used for histopathological and immunohistochemical analyses in prion diseases in animals and man. However, formalin fixation cross-links proteins, reducing disease-associated prion protein (PrP(Sc)) immunolabelling. To detect PrP(Sc) in animals naturally affected with bovine spongiform encephalopathy (BSE) and scrapie, we applied minimal pretreatment with sodium hydroxide (NaOH). This simple pretreatment, combined with enzymatic digestion using proteinase K (PK), was equally effective in the detection of PrP(Sc) in FFPE tissue, and superior in terms of speed, compared with the usual autoclaving method. The most effective results, without any section loss, were obtained with 10 μg/ml PK in phosphate buffered saline containing 0.1% Triton-X at room temperature for 10 min and 150 mM NaOH at 60 °C for 10 min. By this simple procedure, PrP(Sc) was visualized in the brain of animals with BSE and scrapie using a range of anti-PrP primary antibodies.

Detection of classical and atypical/Nor98 scrapie by the paraffin-embedded tissue blot method

The paraffin-embedded tissue (PET) blot method was used to investigate sections of the central nervous system and lymphatic tissues from 24 cases of classical scrapie and 25 cases of atypical/Nor98 scrapie in sheep and four healthy control sheep. The PET blot detected deposits of PrP(Sc) in the brain tissue of all 49 sheep with scrapie but no PrP(Sc) labelling could be detected in the control sheep. By contrast, not all the atypical/Nor98 scrapie cases were detectable by immunohistochemistry. The high sensitivity of the PET blot method made it possible to observe that in some atypical/Nor98 cases, deposits of PrP(Sc) may be restricted to supratentorial brain structures and that the diagnosis may be missed when only testing the obex area, where deposits are common in classical scrapie, and the cerebellar structures, where deposits are considered to be common in atypical/Nor98 cases.

State of the art in antigen retrieval for immunohistochemistry

The masking effects of antigens by chemical fixation, processing, embedding media interactions, represent a serious problem for immunohistochemical purposes. Fortunately, different approaches in antigen retrieval exist. These techniques are relatively recent and continuously expanding. This review focuses on the present state of the art in antigen retrieval methods for immunohistochemistry in light and electron microscopy. Moreover, a brief discussion on the chemical aspects of fixation, mechanism of retrieval, as well as its efficacy, is given.

Cryo-immunogold electron microscopy for prions: toward identification of a conversion site

Prion diseases are caused by accumulation of an abnormally folded isoform (PrP(Sc)) of the cellular prion protein (PrP(C)). The subcellular distribution of PrP(Sc) and the site of its formation in brain are still unclear. We performed quantitative cryo-immunogold electron microscopy on hippocampal sections from mice infected with the Rocky Mountain Laboratory strain of prions. Two antibodies were used: R2, which recognizes both PrP(C) and PrP(Sc); and F4-31, which only detects PrP(C) in undenatured sections. At a late subclinical stage of prion infection, both PrP(C) and PrP(Sc) were detected principally on neuronal plasma membranes and on vesicles resembling early endocytic or recycling vesicles in the neuropil. The R2 labeling was approximately six times higher in the infected than the uninfected hippocampus and gold clusters were only evident in infected tissue. The biggest increase in labeling density (24-fold) was found on the early/recycling endosome-like vesicles of small-diameter neurites, suggesting these as possible sites of conversion. Trypsin digestion of infected hippocampal sections resulted in a reduction in R2 labeling of >85%, which suggests that a high proportion of PrP(Sc) may be oligomeric, protease-sensitive PrP(Sc).

Enzyme-labeled antigen method: histochemical detection of antigen-specific antibody-producing cells in tissue sections of rats immunized with horseradish peroxidase, ovalbumin, or keyhole limpet hemocyanin

The enzyme-labeled antigen method is a histochemical technique that visualizes antigen-specific antibody-producing cells in tissue sections, originally documented in 1968. In this study, we attempted to reemerge this hidden but potentially useful method in rat models immunized with horseradish peroxidase (HRP), ovalbumin (OA), or keyhole limpet hemocyanin (KLH). After repeated immunization in footpads, popliteal, groin, and axillary lymph nodes and spleen were sampled. Paraformaldehyde-prefixed frozen sections were incubated with HRP, biotinylated OA, or biotinylated KLH. Proteinase K pretreatment and the secondary use of HPR-labeled streptavidin were applied in the latter two situations. Plasma cells producing antigen-specific antibodies were visualized. Proportions of antigen-specific antibody-producing cells in total plasma cells shown with the immunoperoxidase method for rat immunoglobulins were evaluated. The percentage of antigen-specific plasma cells reached approximately 50% of total plasma cells in the regional lymph nodes. The specificity was confirmed by (a) negativity in non-immune rat tissue, (b) negativity with indifferent antigen probes, and (c) abolishment of the reactivity with the corresponding rat serum. In buffered formalin-fixed, paraffin-embedded tissues, fewer plasma cells were labeled for HRP and KLH antibody reactivity after strong proteolysis and prolonged incubation. Expectedly, this method allows us to observe antigen-specific antibody-producing cells under varied pathological conditions.

Human prion diseases: from antibody screening to a standardized fast immunodiagnosis using automation

Demonstration of pathological prion protein accumulation in the central nervous system is required to establish the diagnosis of transmissible subacute encephalopathies. In humans, this is frequently achieved using prion protein immunohistochemistry in paraffin-embedded tissue, a technique that requires multiple epitope retrieval and denaturing pretreatments. In addition to being time-consuming, this procedure induces tissue alterations that preclude accurate morphological examination. The aim of this study was to simplify prion protein immunohistochemistry procedure in human tissue, together with increased sensitivity and specificity. We screened a panel of 50 monoclonal antibodies produced using various immunogens (human and ovine recombinant prion protein, prion protein peptides, denatured scrapie-associated fibrils from 263K-infected Syrian hamsters) and directed against different epitopes along the human prion protein sequence. A panel of different forms of genetic, infectious and sporadic transmissible subacute encephalopathies was assessed. The monoclonal 12F10 antibody provided a high specificity and fast immunodiagnosis with very limited denaturing pretreatments. A standardized and reliable fast immunostaining procedure was established using an automated diagnostic system (Nexes, Ventana Medical Systems) and allowed prion protein detection in the central nervous system and in tonsil biopsies. It was evaluated in a series of 300 patients with a suspected diagnosis of transmissible subacute encephalopathies and showed high sensitivity and specificity.

Species-specificity of a panel of prion protein antibodies for the immunohistochemical study of animal and human prion diseases

Monoclonal antibodies to the prion protein (PrP) have been of critical importance in the neuropathological characterization of PrP-related disease in men and animals. To determine the influence of species-specific amino-acid substitutions recognized by monoclonal antibodies, and to investigate the immunohistochemical reactivity of the latter, analyses were carried out on brain sections of cattle with bovine spongiform encephalopathy, sheep with scrapie, mice infected with scrapie, and human beings with Creutzfeldt-Jakob disease (CJD) or Gerstmann-Sträussler-Sheinker disease (GSS). Immunoreactivity varied between the antibodies, probably as the result of differences in the amino-acid sequence of the prion protein in the various species. Some monoclonal antibodies against mouse recombinant PrP gave strong signals with bovine, ovine and human PrP(Sc), in addition to murine PrP(Sc), even though the amino-acid sequences determined by the antibody epitope are not fully identical with the amino-acid sequences proper to the species. On the other hand, in certain regions of the PrP sequence, when the species-specificity of the antibodies is defined by one amino-acid substitution, the antibodies revealed no reactivity with other animal species. In the region corresponding to positions 134-159 of murine PrP, immunohistochemical reactivity or species-specificity recognized by the antibodies may be determined by one amino acid corresponding to position 144 of murine PrP. Not all epitopes recognized by a monoclonal antibody play an important role in antigen-antibody reactions in immunohistochemistry. The presence of the core epitope is therefore vital in understanding antibody binding ability.

Heat-induced antigen retrieval: mechanisms and application to histochemistry

Since the introduction of the fluorescence-labeled antibody method by Coons et al. [Immunological properties of antibody containing a fluorescent group. Proc Soc Exp Biol Med 47, 200-2002], many immunohistochemical methods have been refined to obtain high sensitivity with low background staining at both light and electron microscopic levels. Heat-induced antigen retrieval (HIAR) reported by Shi et al. in the early 1990s has greatly contributed to immunohistochemical analysis for formalin-fixed and paraffin-embedded (FFPE) materials, particularly in the field of pathology. Although antigen retrieval techniques including enzyme digestion, treatment with protein denaturants and heating have been considered tricky and mysterious techniques, the mechanisms of HIAR have been rapidly elucidated. Heating cleaves crosslinks (methylene bridges) and add methylol groups in formaldehyde-fixed proteins and nucleic acids and extends polypeptides to unmask epitopes hidden in the inner portion of antigens or covered by adjacent macromolecules. In buffers having an appropriate pH and ion concentration, epitopes are exposed without entangling the extended polypeptides during cooling process, since polypeptides may strike a balance between hydrophobic attraction force and electrostatic repulsion force. Recent studies have demonstrated that HIAR is applicable for immunohistochemistry with various kinds of specimens, i.e., FFPE materials, frozen sections, plastic-embedded specimens, and physically fixed tissues at both the light- and electron-microscopic levels, and have suggested that the mechanism of HIAR is common to aldehyde-fixed and aldehyde-unfixed materials. Furthermore, heating has been shown to be effective for flow cytometry, nucleic acid histochemistry (fluorescein in situ hybridization (FISH), in situ hybridization (ISH), and terminal deoxynucleotidyl transferase-mediated nick labeling (TUNEL)), and extraction and analysis of macromolecules in both FFPE archive materials and specimens processed by other procedures. In this article, we review mechanism of HIAR and application of heating in both immunohistochemistry and other histochemical reactions.

Immunohistochemistry for the prion protein: comparison of different monoclonal antibodies in human prion disease subtypes

Demonstration of the abnormal form of the prion protein (PrP) in the brain confirms the diagnosis of human prion disease (PrD). Using immunohistochemistry, we have compared ten monoclonal antibodies in PrD subtypes including sporadic and variant Creutzfeldt-Jakob disease (CJD), fatal familial insomnia, Alzheimer's disease (AD), and control brains. CJD subgroups were determined using Western blot analysis for the protease-resistant PrP type in combination with sequencing to determine the genotype at the methionine/valine polymorphism at codon 129 of the prion protein gene. None of the antibodies labeled given subgroups exclusively, but the intensity of immunoreactivity varied among morphologically distinct types of deposit. Fine granular or synaptic PrP deposits stained weakly or not at all with antibodies against the N-terminus of PrP, and were visible in one case only with 12F10 and SAF54. Coarser and plaque type deposits were immunolabeled with all antibodies. The immunostaining patterns appear characteristic for the disease subgroups. Labeling of certain neurons in all cases irrespective of disease, and staining at the periphery and/or throughout the senile plaques of AD patients were also noted. Antibodies such as 6H4 and 12F10 failed to give this type of labeling and are therefore less likely to recognise non-pathological PrP material in immunohistochemistry.

Effective antigen-retrieval method for immunohistochemical detection of abnormal isoform of prion proteins in animals

For immunohistochemistry of the prion diseases, several pretreatment methods to enhance the immunoreactivity of human and animal abnormal proteinase-resistant prion protein (PrP(Sc)) on the tissue sections have been employed. The method of 121 degree C hydrated autoclaving pretreatment or the combination method of 121 degree C hydrated autoclaving with a certain chemical reagent (formic acid or proteinase K, etc) are now widely used. We found that an improved hydrated autoclaving method at 135 degrees C, more effectively enhanced PrP(Sc) immunoreactivity for the antibodies recognizing the linear epitope. In addition, this method was more effective for the long-term fixation samples as compared with other previous methods. However, this modified method could not retrieve PrP(Sc) antigenic epitopes composed of conformational structures or several discontinuous epitopes. We describe the comparative studies between our improved method and other antigen-retrieval procedures reported previously. Based on the differences of reaction among the antibodies, we also discuss the mechanisms of the hydrated autoclaving methods to retrieve PrP(Sc) immunoreactivity.

Antibodies that label paraffin-embedded mouse tissues: a collaborative endeavor

Histology and immunohistochemistry are important tools in the study of human diseases and their respective animal models. The study of mouse models has been hampered by the absence of a large set of mouse-specific antibodies adapted to paraffin-embedded tissues. A total of 196 antibodies were tested on paraffin-embedded mouse tissues preserved in five different fixatives (Fekete's acid-alcohol-formalin, 10% neutral buffered formalin, 4% paraformaldehyde, IHC Zinc Fixative, and Bouin's fixative). The antibodies were targeted to proteins of the cytoplasm (n = 100), plasma membrane (n = 48), nucleus (n = 36), extracellular compartment (n = 5), cytoplasm/cell membrane (n = 4), and viral proteins (n = 3). A total of 83 antibodies provided an adequate signal to noise ratio. Of these, adequate labeling required heat-mediated epitope retrieval or enzymatic digestion for 32 and 8 antibodies, respectively. Epitope recognition was best for tissues fixed with Fekete's acid-alcohol-formalin. However, some proteins could be detected only in IHC Zinc Fixative, confirming that there is no single fixative suitable for the preservation of all epitopes. Four of 13 antibodies that failed to label their cellular targets on tissue sections successfully labeled whole-mount tissues, indicating that tissue processing plays an important role in epitope degradation. Regularly updated information on immunohistochemistry of normal and neoplastic mouse tissues is accessible online at (http://tumor.informatics.jax.org); links to antibody suppliers' web sites are provided.

Quantitative Study of Spongiform Change in Putamen of 24 Cases of Creutzfeldt-Jakob Disease

Creutzfeldt-Jakob disease (CJD) is characterized by 4 main neuropathological lesions: spongiform change, neuronal loss, astrocytic gliosis, and accumulation of pathological prion protein (PrPsc), which is partially protease-resistant (PrPres). This study focused on spongiform change (SC) in the putamen. Because SC varies from case to case, we investigated whether its quantification could provide relevant criteria to discriminate types of PrPres in CJD. SC was quantified in 24 CJD cases, 12 with PrPres type 1 (CJD-PrP1) and 12 with PrPres type 2 (CJD-PrP2), compared to 25 control cases. The study was performed by direct microscopy examination (DME) and by semiautomatic quantification (SAQ) using shape and size criteria previously described. These criteria were suitable for SC quantification in putamen in the majority of cases, except for those with microspongiosis. The results obtained by DME and SAQ methods were correlated and SC scores were compared to the types of PrPres. Sporadic CJD cases with PrPres type 2 were more affected by SC than type 1, suggesting that putamen could be a preferential site to distinguish type 1 from type 2 histologically. The origin of the difference in SC intensity according to the type of PrPres is discussed in terms of host and strain factors.

Antiaggregating antibody raised against human PrP 106-126 recognizes pathological and normal isoforms of the whole prion protein

Antibodies to the prion protein (PrP) have been critical to the neuropathological and biochemical characterization of PrP-related degenerative diseases in humans and animals. Although PrP is highly conserved evolutionarily, there is some sequence divergence among species; as a consequence, anti-PrP antibodies have a wide spectrum of reactivity when challenged with PrP from diverse species. We have produced an antibody [monoclonal antibody (mAb) 2-40] raised against a synthetic peptide corresponding to residues (106-126 of human PrP and have characterized it by epitope mapping, Western immunoblot analysis, and immunohistochemistry. The antibody recognizes not only human PrP isoforms but also pathological PrP from all species tested (i.e., sheep, hamsters, and mice). Together with the fact that it recognizes the whole PrP in both cellular and scrapie isoforms, mAb 2-40 may be helpful in studying conformational changes of the PrP, as well as establishing a possible connection between human and animal diseases.