A method for measurements of the efficiency of immunogold labelling of epoxy-embedded proteins subjected to different retrieval techniques

Evidence of Human Parvovirus B19 Infection in the Post-Mortem Brain Tissue of the Elderly

After primary exposure, the human parvovirus B19 (B19V) genome may remain in the central nervous system (CNS), establishing a lifelong latency. The structural characteristics and functions of the infected cells are essential for the virus to complete its life cycle. Although B19V has been detected in the brain tissue by sequencing PCR products, little is known about its in vivo cell tropism and pathogenic potential in the CNS. To detect B19V and investigate the distribution of its target cells in the CNS, we studied brain autopsies of elderly subjects using molecular virology, and optical and electron microscopy methods. Our study detected B19V in brain tissue samples from both encephalopathy and control groups, suggesting virus persistence within the CNS throughout the host’s lifetime. It appears that within the CNS, the main target of B19V is oligodendrocytes. The greatest number of B19V-positive oligodendrocytes was found in the white matter of the frontal lobe. The number was significantly lower in the gray matter of the frontal lobe (p = 0.008) and the gray and white matter of the temporal lobes (p < 0.0001). The morphological changes observed in the encephalopathy group, propose a possible B19V involvement in the demyelination process.

Heat-induced Antigen Retrieval in Conventionally Processed Epon-embedded Specimens: Procedures and Mechanisms

We studied the effectiveness of heat-induced antigen retrieval (HIAR) in conventionally processed, epon-embedded specimens and the mechanisms of HIAR in the specimens. Frozen sections were first immunostained to examine the possibility of using HIAR for 18 antigens to avoid the effects of epoxy resin embedment. The antigenicity of 7 out of 18 antigens was retrieved with glutaraldehyde fixation followed by osmium tetroxide treatment whereas none were retrieved with glutaraldehyde fixation without post-osmication. Six antigens also exhibited positive immunostaining in semi-thin epon sections when the sections were deplasticized with sodium ethoxide followed by autoclaving. In the immunoelectron microscopy with the post-embedding method, positive reactions with fine ultrastructures were obtained using HIAR without deplasticization. These results suggested that osmium tetroxide binds to ethylene double bonds (which are introduced into protein crosslinks by glutaraldehyde) and forms an extremely stable resonance interaction with the Schiff bases, thus destabilizing the protein crosslinks. Heating also further degrades these crosslinks. The present study demonstrated that archival epon blocks can be useful resources for immunohistochemical studies for both light and electron microscopy.

Development of an immunochromatographic strip for the detection of antibodies against Porcine circovirus-2

A rapid (<5 min) immunochromatographic strip using a colloidal gold–labeled antigen probe was successfully developed and applied for the detection of Porcine circovirus-2 (PCV-2) antibodies in swine. Recombinant Cap protein truncated nuclear localization signal of PCV-2, was expressed and labeled with colloidal gold. This conjugate was dispensed on a conjugate pad as the detector. Staphylococcal protein A and purified porcine anti–PCV-2 antibodies were blotted on a nitrocellulose membrane for the test and control lines, respectively. Sensitivity and specificity of this strip test was evaluated using PCV-2 antisera as well as other sera from pigs infected with a variety of swine viruses. For the validation of this strip test, 500 clinical swine serum samples were assessed both by the strip and a commercial enzyme-linked immunosorbent assay (ELISA) kit. The agreement between the immunochromatographic strip and ELISA kit was 94.00%. This strip possesses high sensitivity and specificity and may be useful as a candidate for rapid diagnosis of PCV-2 antibodies in the field.

Quantum dot immunocytochemical localization of somatostatin in somatostatinoma by Widefield Epifluorescence, super-resolution light, and immunoelectron microscopy

Quantum dot nanocrystal probes (QDs) have been used for detection of somatostatin hormone in secretory granules of somatostatinoma tumor cells by immunofluorescence light microscopy, super-resolution light microscopy, and immunoelectron microscopy. Immunostaining for all modalities was done using sections taken from an epoxy resin-embedded tissue specimen and a similar labeling protocol. This approach allowed assessment of labeling at light microscopy level before examination at super-resolution and electron microscopy level and was a significant aid in interpretation. Etching of ultrathin sections with saturated sodium metaperiodate was a critical step presumably able to retrieve some tissue antigenicity masked by processing in epoxy resin. Immunofluorescence microscopy of QD-immunolabeled sections showed somatostatin hormone localization in cytoplasmic granules. Some variable staining of tumor gland-like structures appeared related to granule maturity and dispersal of granule contents within the tumor cell cytoplasm. Super-resolution light microscopy demonstrated localization of somatostatin within individual secretory granules to be heterogeneous, and this staining pattern was confirmed by immunoelectron microscopy.

Development of an immunochromatographic strip for the detection of antibodies against foot-and-mouth disease virus serotype O

An immunochromatographic strip was developed for the serological detection of type O foot-and-mouth disease (FMD) in swine. In the strip, the expressed protein of VP1, the main protective antigen of FMDV, labeled with colloidal gold was used as the detector, the staphylococcal protein A (SPA) and swine anti-foot-and-mouth disease virus (FMDV) antibody were blotted on the nitrocellulose membrane for the test and control lines, respectively. 296 swine serum samples were collected to evaluate the characteristics of the strip in comparison with existing commercial liquid-phage blocking ELISA (LPB ELISA) kit and peptide ELISA kit. The strip was shown to be of high specificity and sensitivity. Furthermore, the dipstick assay based on the strip is rapid (5 min) and easy to perform with no requirement of professional skills, reagents nor equipment. This suggests that the immunochromatographic strip is an acceptable alternative for use in clinical laboratories lacking specialized equipment and for field diagnosis.

Establishment of a standardized post-embedding method for immunoelectron microscopy by applying heat-induced antigen retrieval

We have developed a new standardized method for the post-embedding immunoelectron microscopy using the same fixation, antigen retrieval and image contrasting procedures. Tissues were fixed with 4% formaldehyde containing 2.5 mM CaCl(2), 1.25 mM MgCl(2) in a 0.1 M 4-(2-hydroxyethyl)-piperazineethanesulfonic acid (HEPES) buffer (pH 7.4) for 2 h and then with the same fixative composition in 0.1 M HEPES buffer (pH 8.5) overnight at room temperature. Vehicle osmolarity of fixatives was adjusted to 300-330 mOsm by adding glucose. The specimens were dehydrated with dimethylformamide on ice and embedded in LR-White resin. Ultrathin sections were heated in a 20 mM Tris-HCl buffer (pH 9.0) for 1-2 h at 95 degrees C. After immuno-gold labeling, the sections were treated with 2% glutaraldehyde containing 0.05% tannic acid in a 0.1 M phosphate buffer (pH 5.5) for 5 min and with a 1% OsO(4)/0.1 M phosphate buffer (pH 7.4) for 5 min, and then they were double stained with uranyl acetate and lead citrate. The standardized method yielded strong and reproducible immunoreactions for soluble, membrane-bound and filamentous proteins showing an excellent image contrast without destruction of the fine structures.

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.

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.

Development of a One-Step Strip Test for the Diagnosis of Chicken Infectious Bursal Disease

A rapid diagnostic strip for chicken infectious bursal disease (IBD) was developed based on membrane chromatography using high-affinity monoclonal antibodies directed to chicken infectious bursal disease virus (IBDV). The diagnostic strip has high specificity for detection of chicken IBDV antigen and recognizes a variety of the virus isolates, including virulent and attenuated strains, with no cross-reactivity to other viruses, such as Newcastle disease virus, Marek's disease virus, infectious bronchitis virus, infectious laryngotracheitis virus, and egg-drop-syndrome virus. The results showed that its specificity was highly consistent with the agar-gel precipitation test (AGP). The diagnostic strip detected as low as 800 median egg lethal dose (ELD50) viruses in the IBDV BC6/85-infected sample, which was comparable with AC-ELISA (400 ELD50) and 32 times more sensitive than the AGP test (2.56 x 10(4) ELD50). In experimental infection, IBDV was detected in the bursa as early as 36 hr postinfection with the diagnostic strip before the clinical signs and gross lesions appeared. It takes only 1-2 min to do a strip test to detect chicken IBDV antigen after the specimen is grounded in a whirl pack with finger massage.