Effects of Delayed or Prolonged Fixation on Immunohistochemical Detection of Bovine Viral Diarrhea Virus Type I in Skin of Two Persistently Infected Calves

Effect of formalin-fixation and paraffin-embedded tissue storage times on RNAscope in situ hybridization signal amplification

RNAscope in situ hybridization (ISH) detects target RNA in formalin-fixed, paraffin-embedded (FFPE) tissues. Protocols suggest that prolonged FFPE storage and formalin fixation may impact signal detection, potentially limiting the utility of RNAscope ISH in retrospective studies. To develop parameters for RNAscope use with archived specimens, we evaluated the effect of formalin-fixation time by measuring the signal of a reference gene (16srRNA) in selected tissues fixed in 10% neutral-buffered formalin for 1, 2, 3, 5, 7, 10, 14, 21, 28, 60, 90, 180, and 270 d. The signal intensity and percent area of signal decreased after 180 d. Tissues had detectable signal at 180 d but not at 270 d of formalin fixation. To assess target detection in paraffin blocks, we qualitatively compared the signal of canine distemper virus (CDV) antigen via immunohistochemistry and CDV RNA via RNAscope ISH in replicate sections from blocks stored at room temperature for 6 mo, 1, 3, 6, 8, 11, 13, and 15 y; RNA was detected in FFPE tissues stored for up to 15 y. Our results demonstrate that RNAscope ISH can detect targets in tissues with prolonged paraffin storage intervals and formalin-fixation times.

Virtual histological staining of unlabeled autopsy tissue

Traditional histochemical staining of post-mortem samples often confronts inferior staining quality due to autolysis caused by delayed fixation of cadaver tissue, and such chemical staining procedures covering large tissue areas demand substantial labor, cost and time. Here, we demonstrate virtual staining of autopsy tissue using a trained neural network to rapidly transform autofluorescence images of label-free autopsy tissue sections into brightfield equivalent images, matching hematoxylin and eosin (H&E) stained versions of the same samples. The trained model can effectively accentuate nuclear, cytoplasmic and extracellular features in new autopsy tissue samples that experienced severe autolysis, such as COVID-19 samples never seen before, where the traditional histochemical staining fails to provide consistent staining quality. This virtual autopsy staining technique provides a rapid and resource-efficient solution to generate artifact-free H&E stains despite severe autolysis and cell death, also reducing labor, cost and infrastructure requirements associated with the standard histochemical staining.

Methods Optimization for Routine Sciatic Nerve Processing in General Toxicity Studies

Recent "best practice" recommendations for peripheral nervous system sampling and processing provide guidance regarding nerve preparation for animal toxicity studies. This study explored the impact of delayed fixation, type of fixative, processing cycle times, starting ethanol concentration, and water bath temperature to improve nerve preservation in routinely prepared (paraffin-embedded, hematoxylin and eosin [H&E]-stained) sections. Sciatic nerves from adult Wistar rats (diameter, 1.04 ± 0.1 mm) and young domestic pigs (diameter 5.9 ± 1.2 mm) fixed at necropsy ("0" hours) or 3, 6, 12, or 24 hours after death were immersed in neutral-buffered 10% formalin containing 1.2% methanol (NBF) or methanol-free 4% formaldehyde (MFF) at room temperature. After fixation for 24 hours (rat) or 48 hours (pig), specimens were processed into paraffin, and ∼5-μm-thick sections were flattened on water baths set at 35°C, 40°C, or 45°C before H&E staining. Large-diameter nerves (pig) required longer processing cycles to ensure sufficient paraffin infiltration. For both small-diameter (rat) and large-diameter nerves, structural integrity was optimal if fixation by NBF or MFF occurred within 3 hours and the initial ethanol concentration for tissue processing was lowered to 50%. At all time points, structural preservation of nerve fibers was acceptable using NBF but was better with MFF. Use of a water bath at 35°C reduced processing-related nerve fiber separation within sections.

Optimization of commercially available Zika virus antibodies for use in a laboratory-developed immunohistochemical assay

Zika virus (ZIKV) infection during pregnancy can cause adverse fetal outcomes and severe irreversible congenital birth defects including microcephaly. Immunohistochemistry (IHC) is a valuable diagnostic tool for detecting ZIKV antigens in tissues from cases of fetal loss in women infected with ZIKV, and for providing insights into disease pathogenesis. As a result, there is increasing demand for commercially available ZIKV antibodies for use in IHC assays. ZIKV antibodies were selected and obtained from commercial sources to include both mouse and rabbit hosts, and a variety of antigenic targets. Pretreatment conditions and antibody concentrations resulting in optimal immunohistochemical staining were determined using ZIKV cell control and polymerase chain reaction (PCR)‐confirmed ZIKV case control material (fetal brain tissue). Cross‐reactivity of the antibodies against other flaviviruses (dengue virus serogroups 1–4, yellow fever virus, Japanese encephalitis virus, West Nile virus) and chikungunya virus was also evaluated. Immunostaining using the commercially available antibodies was compared to a previously validated ZIKV IHC assay used for primary diagnosis. Four antibodies demonstrated optimal staining similar to the previously validated ZIKV IHC assay. Two of the four antibodies cross‐reacted with dengue virus, while the other two antibodies showed no cross‐reactivity with dengue, other flaviviruses, or chikungunya virus. Differences in the cross‐reactivity profiles could not be entirely explained by the antigenic target. Commercially available ZIKV antibodies can be optimized for use in IHC testing to aid in ZIKV diagnostic testing and an evaluation of tissue tropism.

MAP2 IHC detection: a marker of antigenicity in CNS tissues

Immunohistochemistry (IHC) is used to detect antibody-specific antigens in tissues; the results depend on the ability of the primary antibodies to bind to their antigens. Therefore, results depend on the quality of preservation of the specimen. Many investigators have overcome the deleterious effects of over-fixation on the binding of primary antibodies to specimen antigens using IHC, but if the specimen is under-fixed or fixation is delayed, false negative results could be obtained despite certified laboratory practices. Microtubule-associated protein 2 (MAP2) is an abundant microtubule-associate protein that participates in the outgrowth of neuronal processes and synaptic plasticity; it is localized primarily in cell bodies and dendrites of neurons. MAP2 immunolabeling has been reported to be absent in areas of the entorhinal cortex and hippocampus of Alzheimer's disease brains that were co-localized with the dense-core type of amyloid plaques. It was hypothesized that the lack of MAP2 immunolabeling in these structures was due to the degradation of the MAP2 antigen by the neuronal proteases that were released as the neurons lysed leading to the formation of these plaques. Because MAP2 is sensitive to proteolysis, we hypothesized that changes in MAP2 immunolabeling may be correlated with the degree of fixation of central nervous system (CNS) tissues. We detected normal MAP2 immunolabeling in fixed rat brain tissues, but MAP2 immunolabeling was decreased or lost in unfixed and delayed-fixed rat brain tissues. By contrast, two ubiquitous CNS-specific markers, myelin basic protein and glial fibrillary acidic protein, were unaffected by the degree of fixation in the same tissues. Our observations suggest that preservation of various CNS-specific antigens differs with the degree of fixation and that the lack of MAP2 immunolabeling in the rat brain may indicate inadequate tissue fixation. We recommend applying MAP2 IHC for all CNS tissues as a pre-screen to assess the quality of the tissue preservation and to avoid potentially false negative IHC results.

Molecular and Immunohistochemical Characterization of Historical Long-Term Preserved Fixed Tissues from Different Human Organs

University and museum collections are very important sources of biological samples that can be used to asses the past and present genetic diversity of many species. Modern genetic and immunohistochemical techniques can be used on long-term preserved fixed tissues from museum specimens to answer epidemiological questions. A proof of principle was established to apply modern molecular genetics and immunohistochemical methods to these old specimens and to verify the original diagnosis. We analysed 19 specimens from our university collection including human organs that had been in fixative for more than 80 years. The tissues originated from lung, colon, brain, heart, adrenal gland, uterus and skin. We isolated amplifiable DNA from these wet preparations and performed mutational analysis of BRAF, KRAS and EGFR. The tissues were also embedded in paraffin and used for modern histology and immunohistochemistry. Our data show that amplifiable DNA is extractable and ranged from 0.25 to 22.77 μg of total DNA. In three specimens BRAFV600E or KRASG12D mutations were found. Additionally, expression of different proteins like vimentin and GFAP was detected immunohistochemical in six investigated specimens. On the basis of our results the original diagnosis was altered in three specimens. Our work showed that it is possible to extract amplifiable DNA suitable for sequence analysis from long-term fixed tissue. Furthermore, histology and immunohistochemistry is feasible in specimens fixed long time ago. We conclude that these old preparations are suitable for further epidemiological research and that our methods open up new opportunities for future studies.

Immunohistochemical detection of a unique protein within cells of snakes having inclusion body disease, a world-wide disease seen in members of the families Boidae and Pythonidae

Inclusion body disease (IBD) is a worldwide disease in captive boa constrictors (boa constrictor) and occasionally in other snakes of the families Boidae and Pythonidae. The exact causative agent(s) and pathogenesis are not yet fully understood. Currently, diagnosis of IBD is based on the light microscopic identification of eosinophilic intracytoplasmic inclusion bodies in hematoxylin and eosin stained tissues or blood smears. An antigenically unique 68 KDa protein was identified within the IBD inclusion bodies, called IBD protein. A validated immuno-based ante-mortem diagnostic test is needed for screening snakes that are at risk of having IBD. In this study, despite difficulties in solubilizing semi-purified inclusion bodies, utilizing hybridoma technology a mouse anti-IBD protein monoclonal antibody (MAB) was produced. The antigenic specificity of the antibody was confirmed and validated by western blots, enzyme-linked immunosorbent assay, immuno-transmission electron microscopy, and immunohistochemical staining. Paraffin embedded tissues of IBD positive and negative boa constrictors (n=94) collected from 1990 to 2011 were tested with immunohistochemical staining. In boa constrictors, the anti-IBDP MAB had a sensitivity of 83% and specificity of 100% in detecting IBD. The antibody also cross-reacted with IBD inclusion bodies in carpet pythons (Morelia spilota) and a ball python (python regius). This validated antibody can serve as a tool for the development of ante-mortem immunodiagnostic tests for IBD.

When tissue antigens and antibodies get along: revisiting the technical aspects of immunohistochemistry--the red, brown, and blue technique

Once focused mainly on the characterization of neoplasms, immunohistochemistry (IHC) today is used in the investigation of a broad range of disease processes with applications in diagnosis, prognostication, therapeutic decisions to tailor treatment to an individual patient, and investigations into the pathogenesis of disease. This review addresses the technical aspects of immunohistochemistry (and, to a lesser extent, immunocytochemistry) with attention to the antigen-antibody reaction, optimal fixation techniques, tissue processing considerations, antigen retrieval methods, detection systems, selection and use of an autostainer, standardization and validation of IHC tests, preparation of proper tissue and reagent controls, tissue microarrays and other high-throughput systems, quality assurance/quality control measures, interpretation of the IHC reaction, and reporting of results. It is now more important than ever, with these sophisticated applications, to standardize the entire IHC process from tissue collection through interpretation and reporting to minimize variability among laboratories and to facilitate quantification and interlaboratory comparison of IHC results.

Influence of prolonged formalin fixation of tissue samples on the sensitivity of chromogenic in situ hybridization

Chromogenic in situ hybridization (ISH) is a commonly used tool in diagnostic pathology to detect pathogens in formalin-fixed, paraffin-embedded (FFPE) tissue sections. Prolonged formalin fixation time was identified to be a limiting factor for the successful detection of nucleic acid from different pathogens, most probably due to the cross-linking activity of formalin between RNA, DNA, and proteins. Therefore, in the current study, the influence of formalin fixation time on ISH signal intensity of 2 viral (Porcine circovirus-2 [PCV-2] and Porcine respiratory and reproductive virus [PRRSV]) and 2 protozoal agents (Cryptosporidium serpentis and Tritrichomonas sp.) was evaluated. Tissue samples were fixed in 7% neutral buffered formaldehyde solution, and at defined intervals, pieces were embedded in paraffin wax and subjected to pathogen-specific ISH. For all 4 pathogens, the signal intensity remained comparable with the starting ISH signal for different periods of fixation (PCV-2: 6 weeks, PRRSV: 23 weeks, C. serpentis: 55 weeks, Tritrichomonas sp.: 53 weeks). Thereafter, the signal started to decline until loss of nucleic acid detection. The influence of increased proteinase K concentrations for inverting the formalin-induced cross-linking activity was examined compared with the standard protocol. With all 4 infectious agents, a 4-fold proteinase K concentration restored the ISH signals to a level comparable with 1 day of fixation. In conclusion, the influence of prolonged formalin fixation on the intensity of detected ISH signal highly depends on the analyzed infectious agent and the pretreatment protocol.

Effects of Prolonged Formalin Fixation on the Immunohistochemical Detection of Infectious Agents in Formalin-Fixed, Paraffin-Embedded Tissues

Immunohistochemistry is commonly used to detect and characterize infectious agents in diagnostic pathology. The principal advantage of immunohistochemistry over other antigen detection techniques is the ability to identify antigen within the context of histologic lesions. Although epitope masking attributed to formalin fixation, especially prolonged fixation, has been considered a limiting factor in diagnostic immunohistochemistry, only a few studies have evaluated the immunohistochemical detection of infectious agents following prolonged formalin fixation. Therefore, the goal of this study was to evaluate the effects of prolonged formalin fixation on the immunohistochemical detection of 21 infectious agents. Tissue slices about 5 mm thick were fixed in 10% neutral-buffered formalin, processed, and paraffin embedded at day 1 or 2 and then at approximately weekly intervals. Three pathologists graded immunoreactivity according to a four-tier grading system: negative, weak, moderate, strong. Canine parvoviral immunoreactivity was markedly decreased following 2, 7, and 10 weeks of fixation in myocardium, small intestine, and spleen, respectively. Bovine respiratory syncytial virus immunoreactivity was markedly decreased following 7 weeks of fixation. Bartonella henselae had an abrupt loss of immunoreactivity following 9 weeks of fixation. Despite variation among time points, immunoreactivity remained moderate to strong throughout the study period for the other 18 antigens. These results suggest that prolonged formalin fixation of up to 7 weeks generally does not limit immunohistochemical detection of infectious agents. However, the effects of prolonged fixation depend on the targeted antigen and the selected antibody. The results of this study further validate the utility and reliability of immunohistochemistry in diagnostic pathology.

Stability of Bovine viral diarrhea virus antigen in ear punch samples collected from bovine fetuses

Fourteen first-calf heifers were tested free of antibodies against Bovine viral diarrhea viruses (BVDV) by serum neutralization and free of BVDV by polymerase chain reaction. Twelve were exposed to BVDV-1b strain CA0401186a at 84-86 days of gestation, and 2 were exposed to mock inoculum and served as negative controls. Fetuses were harvested by cesarean section at 115-117 days of gestation. The 12 fetuses removed from the BVDV-exposed heifers were BVDV positive based on virus isolation from kidney, thymus, cerebellum, and spleen. It can be assumed that these fetuses would have developed into persistently infected calves had they been allowed to go to term. Virus was not isolated from the fetuses of control animals. Ear punch samples were collected from all fetuses at time of harvest. Antigen capture enzyme-linked immunosorbent assay (ACE), using a commercial kit, was performed on ear punch samples that were frozen within 5 hr of collection and stored at -20 degrees C until tested, tested after storage for 7 days at room temperature (18-25 degrees C), or tested after storage for 7 days at 37 degrees C. Samples stored for 7 days at room temperature or 37 degrees C lost an average of 34% of their starting weight. All samples from BVDV isolation-positive fetuses tested positive by ACE, whereas samples from nonexposed fetuses tested negative, regardless of storage conditions. These results suggest that ACE testing of skin samples collected from aborted fetuses and stillborn calves found in the field may represent a practical surveillance method for BVDV-induced reproductive disease.

Effects of prolonged formalin fixation on diagnostic immunohistochemistry in domestic animals

Immunohistochemistry (IHC) is routinely used in diagnostic pathology to detect infectious agents, to immunophenotype neoplastic cells, and to prognosticate neoplastic diseases. Formalin fixation is considered a limiting factor for IHC because formalin can cross-link antigens and mask epitopes. Prolonged formalin fixation is presumed to result in decreased antigen detection; however, this effect has only been evaluated with a few antibodies. The goal of this study was to evaluate the effect of prolonged formalin fixation on the immunohistochemical detection of 61 different antigens. Approximately 5-mm-thick tissue slices were fixed in 10% neutral-buffered formalin. Tissue slices were removed from formalin, processed, and paraffin-embedded at 1-day, 3-day, and then at approximately 1-week intervals. IHC was performed on all sections in tandem after all tissues were processed. Immunoreactions were evaluated by three pathologists according to a four-tier grading system. Immunoreactivity of cytokeratin 7, high-molecular-weight cytokeratin, and laminin was diminished by prolonged formalin fixation. However, immunohistochemical reactivity remained moderate to strong with up to 7 weeks of fixation for all other antibodies. These results suggest that prolonged formalin fixation has minimal effects on antigen detection for most commonly used antibodies. These results further validate the use of IHC in diagnostic pathology.

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.

A survey of bovine viral diarrhea virus testing in diagnostic laboratories in the United States from 2004 to 2005

Bovine viral diarrhea virus (BVDV) has a great economic impact on the United States cattle industry. The Academy of Veterinary Consultants, the American Association of Bovine Practitioners, and the National Cattlemen's Beef Association have called for the goal of BVDV control and eventual eradication in the U.S.A. One of the key factors in such efforts will be the detection of BVDV infections, particularly targeting persistently infected animals. To assess current BVDV detection methods in the U.S.A., 26 veterinary diagnostic laboratories in 23 states were surveyed. Survey questions related to the types of tests currently offered, the number of tests performed, the reasons for test requests, the type of samples used, whether sample pooling was performed, and whether follow-up testing or information regarding bovine viral diarrhea (BVD) management was provided after positive tests. There was no clear consensus on an individual BVDV testing method, the pooling of samples or the retesting of positive animals. Ear-notch antigen capture enzyme-linked immunosorbent assay (ACE) was the test most frequently performed based on the absolute number of tests. However, when the data were adjusted to reflect individual laboratory choices, the number of ACE and immunohistochemistry tests performed on ear notches was nearly equal. Only 55% of diagnostic laboratories provided BVD management information to producers or veterinarians who submitted positive samples. There was no significant difference in the number of positive tests in laboratories that received the majority of their samples for screening purposes versus laboratories that received the majority of their samples because BVDV was suspected based on clinical signs in a herd.

Assessing the effect of sample handling on the performance of a commercial bovine viral diarrhea virus antigen-capture enzyme-linked immunosorbent assay

Handling practices of specimens may affect the sensitivity or specificity of diagnostic tests. In this study, as part of the Voluntary Iowa Bovine Viral Diarrhea Virus Screening Project held in 2006, 2 sample-handling practices were evaluated to determine how they affect the sensitivity and specificity of the antigen-capture enzyme-linked immunosorbent assay (ACE) for bovine viral diarrhea virus (BVDV). The null hypotheses investigated were 1) that maintenance of samples at room temperature would not be associated with decreased sensitivity, and 2) that continued use of a single pair of ear notchers would not be associated with cross-contamination of virus from 1 notch to another and reduce specificity. These hypotheses were tested in 2 studies by collecting known positive and negative samples and giving groups of samples different treatments. The first study used ACE on 4 groups of skin samples, all from a known-positive animal. Each group was subjected to different lengths of time at room temperature, from 24 to 96 hours at 24-hour intervals. No difference in test results was found between specimens subjected to different lengths of time at room temperature. The second study tested the effects of giving 3 different treatments to an ear notcher in between sample collecting (water rinse, Nolvasan solution rinse, or no treatment) on ACE results. No effect on sensitivity or specificity of ACE was observed. No difference in test results was found between the 3 ear-notcher treatment groups. The sample handling practices evaluated appeared to have little impact on test sensitivity or specificity of ACE for BVDV.