Heat-induced antigen retrieval for immunohistochemical reactions in routinely processed paraffin sections

A comprehensive protocol for simplified mouse DRG fixation, processing and F4/80 immunohistochemistry: Overcoming common challenges

BACKGROUND

Dorsal root ganglia (DRGs) contain the cell bodies of sensory neurons and non-neuronal cells that play a role in the pathophysiology of painful inflammatory conditions, such as neuropathic pain. Immunohistochemistry (IHC) is a valuable tool for visualising and quantifying immune cell markers in DRGs, providing important insights into these mechanisms. However, isolating DRGs while preserving cell morphology for IHC staining is technically challenging due to their small size and location within the spinal column.

OBJECTIVE

Using F4/80, a pan monocyte-macrophage marker, we present an optimised protocol for the fixation, harvesting, processing, and IHC staining of formalin-fixed-paraffin-embedded (FFPE) mouse DRGs. This method is designed to maintain tissue integrity and ensure compatibility with downstream histopathological analysis.

NEW METHOD

The entire spinal column of mouse was fixed in 10 % neutral-buffered formalin at room temperature for 24 h before DRG isolation. DRGs were processed for 9 h, and antigen retrieval was performed using proteinase K.

RESULTS

The optimised immersion-fixation approach preserved cellular morphology and antigenicity, ensuring high-quality histological outcomes.

COMPARISON WITH EXISTING METHODS

While transcardial perfusion remains the gold standard for tissue fixation, it is time-intensive, requires training and raises ethical concerns. Our optimised method of whole spinal column fixation with subsequent tissue isolation is non-invasive and reduces the time between death and fixation in comparison to post-isolation fixation. Additionally, it delivers histological quality likely comparable to that of perfusion-based techniques.

CONCLUSION

This protocol is supported by a grading system to help evaluate variables and select conditions best suited to their experimental goals.

Biotransformation and biological fate of magnetic iron oxide nanoparticles for biomedical research and clinical applications

Safe implementation of nanotechnology-based products in biomedical applications necessitates an extensive understanding of the (bio)transformations that nanoparticles undergo in living organisms. The long-term fate in the body is a crucial consideration because it governs potential risks for human health. To accurately predict the life cycle of nanoparticles, their fate after administration into the body-including their (bio)transformations, persistence, and biodegradation-needs to be thoroughly evaluated. Magnetic iron oxide nanoparticles (MIONPs) can enter the body through various routes, including inhalation, ingestion, dermal absorption, and injection. Microscale and nanoscale studies are performed to observe nanomaterial biotransformations and their effect on clinically relevant properties. Researchers are utilizing high-resolution TEM for nanoscale monitoring of the nanoparticles while microscale follow-up approaches comprise quantification tools at the whole organism level and the molecular level. Nanoparticle-cell interactions, including cellular uptake and intracellular trafficking, are key to understanding nanoparticle accumulation in cells and organs. Prolonged accumulation may induce cell stress and nanoparticle toxicity, often mediated through oxidative stress and inflammation. In this review article, the journey of nanoparticles in the body is depicted and their biotransformations and final fate are discussed. Immunohistochemical techniques are particularly valuable in tracking nanoparticle distribution within tissues and assessing their impact at the cellular level. A thorough description of a wide range of characterization techniques is provided to unveil the fate and biotransformations of clinically relevant nanoparticles and to assist in their design for successful biomedical applications.

Protocol to characterize longitudinal gut motility in mice using transit time, tissue harvest, and whole-mount immunostaining

Transit time is a key in vivo metric of gastrointestinal (GI) motility, which is a physiologic readout of cellular communication within the enteric system. Here, we present a protocol to characterize longitudinal gut motility in mice. We describe steps for transit testing, whole-mount immunostaining, and tissue harvest. We then detail procedures for image processing and manual cell counting. This protocol seeks to minimize inter-trial variability while assessing cellular and molecular features that may underpin motility differences between experimental conditions. For complete details on the use and execution of this protocol, please refer to Frith et al.1.

Mitigating Post-Subarachnoid Hemorrhage Complications: Anti-Inflammatory and Anti-Apoptotic Effects of Anakinra in an Experimental Study

Background: Subarachnoid hemorrhage (SAH) is a severe neurological condition with high mortality and morbidity rates, often exacerbated by secondary complications such as inflammation, cerebral vasospasm, and apoptosis. Proinflammatory cytokines, including interleukin-1 (IL-1), tumor necrosis factor-alpha (TNF-α), and interleukin-6 (IL-6), play critical roles in these pathological processes. Anakinra, an IL-1 receptor antagonist, has demonstrated significant anti-inflammatory effects in various disease models. This study aimed to evaluate the efficacy of anakinra in mitigating inflammation, vasospasm, and apoptosis in an experimental rat model of SAH. Methods: Thirty-two male Sprague Dawley rats were divided into four groups: Control (healthy), SAH (no treatment), Saline (0.2 mL saline subcutaneously), and Anakinra (50 mg/kg subcutaneously, twice daily). Proinflammatory markers (CRP, TNF-α, IL-1, IL-6, and fibrinogen) were measured in serum and cerebrospinal fluid (CSF) at 3, 7, and 10 days post-SAH. Basilar artery diameter was evaluated histopathologically, and Caspase-3 expression was assessed immunohistochemically to determine apoptotic activity. Results: SAH significantly increased levels of CRP, TNF-α, IL-1, IL-6, and fibrinogen in both serum and CSF, reduced basilar artery diameter, and elevated Caspase-3 expression compared to the Control group. Saline treatment provided limited improvements, with inflammatory markers and histopathological parameters remaining elevated. Anakinra treatment significantly reduced inflammatory markers, restored basilar artery diameter, and lowered Caspase-3 expression, highlighting its efficacy in mitigating inflammation, vasospasm, and apoptosis. Conclusions: Anakinra effectively suppresses inflammation, alleviates cerebral vasospasm, and inhibits apoptosis in an experimental model of SAH. These findings suggest its potential as a therapeutic agent for managing SAH and its complications. Further research is needed to explore its clinical applicability and long-term effects.

3D fluorescence staining and confocal imaging of low amount of intestinal organoids (enteroids): Protocol accessible to all

The emerging field of 3D organ modeling encounters several imaging issues in particular related to antigen retrieval and sample loss during staining processes. Due to their compact shape, several antibodies fail to penetrate intact organoids or spheroids. Histology of organoids can be approached by paraffin inclusion and sectioning at 5 μm as performed for biopsies. However, to fully understand organoid behavior, including cellular organization, extracellular matrix structure, and their response to treatments, 3D imaging is essential. Here we propose an easy workflow allowing (1) immunostaining with a HIER step, (2) preservation of the intact shape of the organoids, (3) sample immobilization in a focal plane reachable for high resolution/short working distance lenses, and (4) minimizing the risk of loss of precious material.

Systematic comparison of quantity and quality of RNA recovered with commercial FFPE tissue extraction kits

BACKGROUND

FFPE tissue samples are commonly used in biomedical research and are a valuable source for next-generation sequencing in oncology, however, extracting RNA from these samples can be difficult the quantity and quality achieved can impact the downstream analysis. This study compared the effectiveness of seven different commercially available RNA extraction kits specifically designed for use with FFPE samples in terms of the quantity and quality of RNA recovered.

METHODS

This study used 9 samples of FFPE tissue from three different types of tissue (Tonsil, Appendix and lymph node of B-cell lymphoma) to evaluate RNA extraction methods. Three sections of 20 µm of each sample were combined per sample. The slices were distributed in a systematic manner to prevent any biases. Each of the 7 commercially available RNA extraction kits were used according to manufacturer's instructions, with each sample being tested in triplicate resulting in a total of 189 extractions. The concentration, RNA quality score (RQS) and DV200 of each extraction was analysed using a nucleic acid analyser to determine the quantity and quality of the recovered RNA.

RESULTS

This study found that despite processing the FFPE samples in the same standardized way, there were disparities in the quantity and quality of RNA recovered across the different tissue types. Additionally, the study found notable differences in the quantity of RNA recovered when using different extraction kits. In terms of quality, three of the kits performed better than the other four in terms of RQS and DV200 values.

CONCLUSION

Though many laboratories have developed their own protocols for specific tissue types, using commercially available kits is still a popular option. Although these kits use similar processes and extraction procedures, the amount and quality of RNA obtained can vary greatly between kits. In this study, among the kits tested, while the Roche kit, provided a nearly systematic better-quality recovery than other kits, the ReliaPrep FFPE Total RNA miniprep from Promega yielded the best ratio of both quantity and quality on the tested tissue samples.

Multiparameter quantitative analyses of diagnostic cells in brain tissues from tuberous sclerosis complex

The advent of high-dimensional imaging offers new opportunities to molecularly characterize diagnostic cells in disorders that have previously relied on histopathological definitions. One example case is found in tuberous sclerosis complex (TSC), a developmental disorder characterized by systemic growth of benign tumors. Within resected brain tissues from patients with TSC, detection of abnormally enlarged balloon cells (BCs) is pathognomonic for this disorder. Though BCs can be identified by an expert neuropathologist, little is known about the specificity and broad applicability of protein markers for these cells, complicating classification of proposed BCs identified in experimental models of this disorder. Here, we report the development of a customized machine learning pipeline (BAlloon IDENtifier; BAIDEN) that was trained to prospectively identify BCs in tissue sections using a histological stain compatible with high-dimensional cytometry. This approach was coupled to a custom 36-antibody panel and imaging mass cytometry (IMC) to explore the expression of multiple previously proposed BC marker proteins and develop a descriptor of BC features conserved across multiple tissue samples from patients with TSC. Here, we present a modular workflow encompassing BAIDEN, a custom antibody panel, a control sample microarray, and analysis pipelines-both open-source and in-house-and apply this workflow to understand the abundance, structure, and signaling activity of BCs as an example case of how high-dimensional imaging can be applied within human tissues.

Impact of immunohistochemistry staining conditions on the incidence of human epidermal growth factor receptor 2 (HER2)-low breast cancer

We investigated frequencies of HER2-low breast cancer (BC) (immunohistochemistry [IHC] 1+ or 2+ without gene amplification) before and after IHC conditions were modified in order to understand the impact of IHC staining conditions on frequencies of HER2-low BC. Primary BC cases diagnosed at the Yeungnam University Hospital (YUH, n = 728) or Keimyung University Dongsan Hospital (KUDH, n = 290) in 2022 were reviewed, and data on HER2 status and IHC conditions were collected (cohort 1). Both institutions used the 4B5 antibody for HER2 IHC but had different staining protocols. After modifications of the IHC conditions at both institutions, primary BC cases (YUH, n = 324 and KUDH, n = 135) diagnosed from April to July 2023 (cohort 2) were reviewed to assess any changes in the frequency of HER2 status. In cohort 1, of the 728 cases diagnosed at YUH, 556 (76.4%) were HER2-zero, 76 (10.4%) were HER2-low, and 96 (13.2%) were HER2-positive, and of the 290 cases diagnosed at KUDH, 135 (46.6%) were HER2-zero, 82 (28.3%) were HER2-low, and 73 (25.2%) were HER2-positive. Modifications in HER2 IHC staining conditions dramatically increased the frequencies of HER2-low BC in cohort 2 (YUH 38.9% and KUDH 49.6%), but they did not result in significant changes in the HER2-positive rates (YUH 15.4% and KUDH 25.2%) compared to cohort 1. In conclusion, minor modifications in HER2 IHC staining conditions significantly affected the frequency of HER2-low BC but had little impact on the HER2-positivity rate. Each pathology laboratory should verify IHC conditions using control slides (including 1+) to enable the accurate identification of HER2-low BC.

Assessment of equine intestinal epithelial junctional complexes and barrier permeability using a monolayer culture system

Gastrointestinal disease is a leading cause of death in mature horses. A lack of in vitro modeling has impeded the development of novel therapeutics. The objectives of this study were to develop and further characterize a small intestinal monolayer cell culture derived from equine jejunum including establishing normal measurements of intestinal permeability and restitution. Three-dimensional enteroids, derived from postmortem sampling of equine jejunum, were utilized to develop confluent epithelial monolayers. The presence of differentiated intestinal epithelial cell types and tight junctions were confirmed using histology, reverse transcription PCR (RT-PCR), RNAscope, protein immunofluorescence and transmission electron microscopy. Transepithelial resistance (TER) and macromolecule flux were assessed as measurements of paracellular and transcellular permeability. Scratch assays were utilized to model and assess intestinal restitution. Monolayer cell cultures reached 100% confluency by ~5-7 days. Equine jejunum monolayers were confirmed as epithelial in origin, with identification of differentiated intestinal epithelial cell types and evidence of tight junction proteins. Function of the intestinal barrier was supported by acquisition of physiologically normal TER values (179.9 ± 33.7 ohms*cm2) and limited macromolecule flux (22 ± 8.8% at 60 min). Additionally, following a scratch wound, epithelial cell monolayers migrated to close gap defects within 24 h. In conclusion, this study describes the development of a novel intestinal epithelial monolayer cell culture for equine jejunum, and provides evidence of intestinal epithelial cell differentiation, formation of physiologically relevant barrier function and use as a model of intestinal restitution to test potential therapeutics for equine colic.

A Nationwide Study on HER2-Low Breast Cancer in South Korea: Its Incidence of 2022 Real World Data and the Importance of Immunohistochemical Staining Protocols

PURPOSE

Notable effectiveness of trastuzumab deruxtecan in patients with human epidermal growth factor receptor 2 (HER2)-low advanced breast cancer (BC) has focused pathologists' attention. We studied the incidence and clinicopathologic characteristics of HER2-low BC, and the effects of immunohistochemistry (IHC) associated factors on HER2 IHC results.

MATERIALS AND METHODS

The Breast Pathology Study Group of the Korean Society of Pathologists conducted a nationwide study using real-world data on HER2 status generated between January 2022 and December 2022. Information on HER2 IHC protocols at each participating institution was also collected.

RESULTS

Total 11,416 patients from 25 institutions included in this study. Of these patients, 40.7% (range, 6.0% to 76.3%) were classified as HER2-zero, 41.7% (range, 10.5% to 69.1%) as HER2-low, and 17.5% (range, 6.7% to 34.0%) as HER2-positive. HER2-low tumors were associated with positive estrogen receptor and progesterone receptor statuses (p < 0.001 and p < 0.001, respectively). Antigen retrieval times (≥ 36 minutes vs. < 36 minutes) and antibody incubation times (≥ 12 minutes vs. < 12 minutes) affected on the frequency of HER2 IHC 1+ BC at institutions using the PATHWAY HER2 (4B5) IHC assay and BenchMark XT or Ultra staining instruments. Furthermore, discordant results between core needle biopsy and subsequent resection specimen HER2 statuses were observed in 24.1% (787/3,259) of the patients.

CONCLUSION

The overall incidence of HER2-low BC in South Korea concurs with those reported in previously published studies. Significant inter-institutional differences in HER2 IHC protocols were observed, and it may have impact on HER2-low status. Thus, we recommend standardizing HER2 IHC conditions to ensure precise patient selection for targeted therapy.

Pyroxylin-based liquid bandage forms a mechanically active protective film to facilitate skin wound healing in mice

Wound healing requires interplay between cells and molecules. Recent evidence has demonstrated that liquid bandages promote wound healing by forming a protective barrier against contamination, attenuating inflammation, and enhancing re-epithelialization and angiogenesis. In this study, we evaluated the wound healing activity of pyroxylin-based liquid bandage (LiQuiPlast®) in eight-week-old C57BL/6 male mice by generating a single 4 mm diameter full-thickness excisional skin wound on the dorsum. In the LiQuiPlast® group, the liquid bandage was applied on day 0 and was replaced every four days. Wound size was monitored every day for two weeks. The results showed that LiQuiPlast® was mechanically active (induced wound contraction), which promoted a significant wound size reduction (27 %-39 %, compared to the control group) on days 1-4 postinjury. In addition, a significant reduction in wound size was observed again in the LiQuiPlast® group (25 %-29 %, compared to the controls) on days 8-9 postinjury. LiQuiPlast®-treated wounds showed no scab. Immunohistochemistry analyses displayed a reduction in neutrophils and tumor necrosis factor-α levels in LiQuiPlast®-treated wounds, compared to the control group on day 4 postinjury (the inflammatory phase). In addition, LiQuiPlast®-treated mice had enhanced keratinocyte proliferation than control mice during this time. On day 13 postinjury, LiQuiPlast® significantly reduced hypertrophic scarring and enhanced expression and reorganization of collagen fiber compared to control mice. In conclusion, we show that LiQuiPlast® acts as a mechanically active protective film, which promotes moist wound healing by promoting wound contraction, no scab formation, attenuated inflammation, enhanced keratinocyte proliferation, and decreased scarring.

Revealing intact neuronal circuitry in centimeter-sized formalin-fixed paraffin-embedded brain

Tissue-clearing and labeling techniques have revolutionized brain-wide imaging and analysis, yet their application to clinical formalin-fixed paraffin-embedded (FFPE) blocks remains challenging. We introduce HIF-Clear, a novel method for efficiently clearing and labeling centimeter-thick FFPE specimens using elevated temperature and concentrated detergents. HIF-Clear with multi-round immunolabeling reveals neuron circuitry regulating multiple neurotransmitter systems in a whole FFPE mouse brain and is able to be used as the evaluation of disease treatment efficiency. HIF-Clear also supports expansion microscopy and can be performed on a non-sectioned 15-year-old FFPE specimen, as well as a 3-month formalin-fixed mouse brain. Thus, HIF-Clear represents a feasible approach for researching archived FFPE specimens for future neuroscientific and 3D neuropathological analyses.

Walking a thin line between fixation and epitope binding - characterization of antigen retrieval methods suitable for eosinophil and HSV-2 staining in formalin-fixed female reproductive tissue

Antibody-based fluorescence analysis of female reproductive tissues in research of sexually transmitted diseases allows for an in-depth understanding of protein localization, interactions, and pathogenesis. However, in many cases, cryosectioning is not compatible with biosafety regulations; at all times, exposure of lab personnel and the public to potentially harmful pathogens from biological infectious material must be avoided; thus, formaldehyde fixation is essential. Due to formaldehyde's cross-linking properties, protein detection with antibodies can be impeded. To allow effective epitope binding during immunofluorescence of formalin-fixed paraffin-embedded vaginal tissue, we investigated two antigen retrieval methods. We tested these methods regarding their suitability for automated image analysis, facilitating reproducible quantitative microscopic data acquisition in sexually transmitted disease research. Heat-based retrieval at 80°C in citrate buffer proved to increase antibody binding to eosinophil protein and HSV-2 visibly and tissue morphology best, and was the most efficient for sample processing and quantitative analysis.

Using digital pathology to analyze the murine cerebrovasculature

Research on the cerebrovasculature may provide insights into brain health and disease. Immunohistochemical staining is one way to visualize blood vessels, and digital pathology has the potential to revolutionize the measurement of blood vessel parameters. These tools provide opportunities for translational mouse model research. However, mouse brain tissue presents a formidable set of technical challenges, including potentially high background staining and cross-reactivity of endogenous IgG. Formalin-fixed paraffin-embedded (FFPE) and fixed frozen sections, both of which are widely used, may require different methods. In this study, we optimized blood vessel staining in mouse brain tissue, testing both FFPE and frozen fixed sections. A panel of immunohistochemical blood vessel markers were tested (including CD31, CD34, collagen IV, DP71, and VWF), to evaluate their suitability for digital pathological analysis. Collagen IV provided the best immunostaining results in both FFPE and frozen fixed murine brain sections, with highly-specific staining of large and small blood vessels and low background staining. Subsequent analysis of collagen IV-stained sections showed region and sex-specific differences in vessel density and vessel wall thickness. We conclude that digital pathology provides a useful tool for relatively unbiased analysis of the murine cerebrovasculature, provided proper protein markers are used.

In Situ Characterization of Human Follicular Helper CD4 T Cells

The development of an effective humoral response to pathogens and immunogens is a multiphase biological process, which is mediated by the coordinated function of specialized immune cell types in secondary lymphoid organs and particularly in T cell and follicular areas. More specifically, within the follicular/germinal center area, the orchestrated interplay between B cells, follicular helper CD4 T cells (Tfh), and stromal cells triggers a cascade of immune reactions leading to the development of memory B cells and plasma cells able to generate effective, antigen-specific antibodies. The role of Tfh cells in this process is critical. Given the need for vaccines capable to induce antibodies of high affinity, neutralizing activity, and durability, understanding the cellular and molecular mechanisms regulating Tfh cell development is of great importance. Here, we describe novel approaches for the comprehensive understanding of these cells and possible implications for future studies in vaccine development and the understanding of the pathogenesis of relevant diseases.

Can CD133 Be Regarded as a Prognostic Biomarker in Oncology: Pros and Cons

The CD133 cell membrane glycoprotein, also termed prominin-1, is expressed on some of the tumor cells of both solid and blood malignancies. The CD133-positive tumor cells were shown to exhibit higher proliferative activity, greater chemo- and radioresistance, and enhanced tumorigenicity compared to their CD133-negative counterparts. For this reason, CD133 is regarded as a potential prognostic biomarker in oncology. The CD133-positive cells are related to the cancer stem cell subpopulation in many types of cancer. Recent studies demonstrated the involvement of CD133 in the regulation of proliferation, autophagy, and apoptosis in cancer cells. There is also evidence of its participation in the epithelial-mesenchymal transition associated with tumor progression. For a number of malignant tumor types, high CD133 expression is associated with poor prognosis, and the prognostic significance of CD133 has been confirmed in a number of meta-analyses. However, some published papers suggest that CD133 has no prognostic significance or even demonstrate a certain correlation between high CD133 levels and a positive prognosis. This review summarizes and discusses the existing evidence for and against the prognostic significance of CD133 in cancer. We also consider possible reasons for conflicting findings from the studies of the clinical significance of CD133.

Expression of NKX2.2 in Non-Ewing Tumors With Round Cell Morphology

Background Round cell sarcomas pose diagnostic challenges due to overlapping histopathological features, necessitating precise immunohistochemical markers for accurate categorization. NKX2.2 has emerged as a sensitive diagnostic tool, particularly in Ewing sarcoma. This study extends this understanding to various round-cell sarcomas, shedding light on the potential diagnostic utility of NKX2.2 beyond its established role. The nuanced exploration of NKX2.2 expression aims to enhance diagnostic strategies, prognostic assessments, and therapeutic developments in the landscape of sarcoma research. Methodology Cases were retrieved from the surgical pathology and consultation files of Shaukat Khanum Memorial Cancer Hospital and Research Center, Lahore, Pakistan. Representative hematoxylin and eosin-stained slides of six different types of already confirmed tumors, including lymphoblastic lymphoma, neuroblastoma, rhabdomyosarcoma, synovial sarcoma, Wilms tumor, and Ewing sarcoma, were reviewed by a panel of pathologists. Immunohistochemistry, utilizing a rabbit anti-NKX2.2 monoclonal antibody, was performed on formalin-fixed paraffin-embedded tissue sections. The presence of NKX2.2 was defined as moderate or high nuclear immunoreactivity in at least 5% of cells. Results The histopathological examination revealed characteristic features in each sarcoma subtype, aligning with established diagnostic criteria. In Lymphoblastic lymphoma, T-cell lineage was confirmed through TdT expression, while the atypical finding of focal NKX 2.2 expression hinted at genetic diversity. Neuroblastoma exhibited the expected salt and pepper chromatin pattern, with NKX 2.2 expression raising questions about its prognostic significance. Rhabdomyosarcoma presented primitive cells expressing desmin, and NKX 2.2 focal expression echoed previous subtype-associated studies. Synovial sarcoma displayed both monophasic and biphasic growth patterns and TLE1 expression, with NKX 2.2 variation suggesting tumor heterogeneity. In Wilms tumor, the characteristic WT1 expression was observed, while NKX2.2's absence reaffirmed its irrelevance in this context. Ewing sarcoma displayed the anticipated homogenous cell population, strong NKX2.2 expression, and CD99 positivity across various sites. Furthermore, age and gender impact on this range of sarcomas found no significant relation with an expression of NKX2.2. Conclusion In conclusion, the diverse expression profiles of diagnostic markers discovered in this study, particularly the atypical expression of NKX2.2 beyond its established role in Ewing sarcoma, signify a significant advancement. This unique finding accentuates the potential diagnostic importance of NKX2.2 in various sarcomas, presenting a novel dimension to our understanding of these malignancies.

Impact of Decalcification, Cold Ischemia, and Deglycosylation on Performance of Programmed Cell Death Ligand-1 Antibodies With Different Binding Epitopes: Comparison of 7 Clones

Programmed cell death ligand-1 (PD-L1) expression levels in patients' tumors have demonstrated clinical utility across many cancer types and are used to determine treatment eligibility. Several independently developed PD-L1 immunohistochemical (IHC) predictive assays are commercially available and have demonstrated different levels of staining between assays, generating interest in understanding the similarities and differences between assays. Previously, we identified epitopes in the internal and external domains of PD-L1, bound by antibodies in routine clinical use (SP263, SP142, 22C3, and 28-8). Variance in performance of assays utilizing these antibodies, observed following exposure to preanalytical factors such as decalcification, cold ischemia, and duration of fixation, encouraged additional investigation of antibody-binding sites, to understand whether binding site structures/conformations contribute to differential PD-L1 IHC assay staining. We proceeded to further investigate the epitopes on PD-L1 bound by these antibodies, alongside the major clones utilized in laboratory-developed tests (E1L3N, QR1, and 73-10). Characterization of QR1 and 73-10 clones demonstrated that both bind the PD-L1 C-terminal internal domain, similar to SP263/SP142. Our results also demonstrate that under suboptimal decalcification or fixation conditions, the performance of internal domain antibodies is less detrimentally affected than that of external domain antibodies 22C3/28-8. Furthermore, we show that the binding sites of external domain antibodies are susceptible to deglycosylation and conformational structural changes, which directly result in IHC staining reduction or loss. The binding sites of internal domain antibodies were unaffected by deglycosylation or conformational structural change. This study demonstrates that the location and conformation of binding sites, recognized by antibodies employed in PD-L1 diagnostic assays, differ significantly and exhibit differing degrees of robustness. These findings should reinforce the need for vigilance when performing clinical testing with different PD-L1 IHC assays, particularly in the control of cold ischemia and the selection of fixation and decalcification conditions.

Histological assessment of intestinal injury by ionizing radiation

Given the potential risk of radiological terrorism and disasters, it is essential to develop plans to prepare for such events. In these hazardous scenarios, radiation-induced gastrointestinal (GI) syndrome is one of the many manifestations that may happen after the organism is exposed to a lethal dose of ionizing radiation. Therefore, it is critical to better understand how the intestinal tissues initiate and orchestrate regeneration following severe radiation injury. In this chapter, we aimed to provide several key considerations for researchers who utilize histological assessment to study radiation-induced intestinal injury. Rigor and reproducibility are critical in experimental design and can be achieved by maintaining proper radiation administration, maintaining consistency in sample collection, and selecting and using appropriate controls. We also provided technical details of histological preparation of the intestines with tips on dissecting, cleaning, fixing, and preserving. Step-by-step descriptions of both bundling and Swiss rolling are provided with discussion on how to choose between the two approaches. In the following section, we detailed several histological assessment methods and then provided suggestions on how to use histological assessment to study cellular dynamics in the small intestines. Finally, we touched on some non-histological assessments. We hope that the information provided in this chapter will contribute to the research society of radiation-induced intestinal injury with an ultimate goal of promoting the development of radiation countermeasures against the GI acute radiation syndrome.

Heat-induced antigen retrieval utilizing modified Tris-EDTA buffer for reprobing of Western blots on nitrocellulose paper

The development of heat-induced antigen retrieval technologies with Tris-EDTA buffer has dramatically improved immunostaining of specific antigens for routine immunohistochemical detection (Krenacs et al., 2010) [1]. However, little evidence exists on whether heat-Induced antigen retrieval utilizing Tris-EDTA buffer can strip western blot (WB) membranes and allow sequential reprobing. Here, we serendipitously discover that ∼95 °C Tris-EDTA buffer with 0.01% Tween 20 could repeatedly strip the Nitrocellulose membranes (NC). After electroblotting, NC blots were soaked into Tris-EDTA stripping buffer (∼95 °C, 10-25min) and we could perform at least five rounds (the following antibodies used: Vinculin, Atg7, Caspase-3, UBA5, JNK and ERK1/2) stripping in sequential chemiluminescent detections. The NC membranes also show clear western signals and background without losing transferred proteins during the reprobing process of WB. Hence, this study report additional new roles of the heat-Induced antigen retrieval Tris-EDTA buffer with 0.01% Tween 20. The method is simpler, more affordable and harmless for the nitrocellulose paper, which will be helpful for effective reprobing in western blotting applications.

Increasing temperature denatures canine IgG reducing its ability to inhibit heartworm antigen detection

BACKGROUND

Immune complexing of target antigen to high affinity host antibody is recognized to impact the sensitivity of commercial heartworm antigen tests. Published information describing the effect of heat on interfering canine host antibodies is lacking. Immune complex dissociation (ICD) by heat treatment of serum for samples initially testing negative for heartworm antigen increases sensitivity of commercial antigen tests, particularly for single sex or low adult infection intensities. In this study the stability and nature of the targeted epitope and mechanism of heat ICD were examined.

METHODS

Canine IgG was isolated using protein-A columns from serum originating from four dogs evaluated after necropsy: one dog with evidence of previously cleared infection and three dogs with confirmed heartworm infections. These dogs were expected to have an excess of antibodies based on negative antigen test and to have no or low antigen optical density, respectively, following heat treatment. Interference of antigen detection on (non-heated) positive serum was evaluated, following 1:1 mixing of antibody/PBS solutions previously heated at 25 °C, 65 °C, 75 °C, 85 °C, 95 °C and 104 °C, compared to positive serum/PBS control measured by optical density using a commercial heartworm antigen ELISA and protein quantification. Live heartworms incubated in media for 72 h provided excretory/secretory antigen for antigen stability studies following heat, endopeptidase digestion and disulfide bond reduction.

RESULTS

Mixing antigen-positive heartworm serum with antibody solutions demonstrated a significant inhibition of antigen detection for antibody solutions previously heated at 25 °C and 65 °C relative to positive serum/PBS control. Antigen detection optical density was restored at or above the control when positive serum was mixed with solutions previously heated at 75 °C, 85 °C, 95 °C and 104 °C. Significant changes occurred in protein levels for antibody solutions heated at 75 °C, 85 °C, 95 °C and 104 °C. Relative stability of antigen from live heartworms in culture was demonstrated following heat, chemical and enzymatic treatment.

CONCLUSIONS

Significant changes in protein levels and antigen binding ability occurred in IgG solutions heated above 65 °C. The findings confirm heat denaturation of antibodies as the suspected mechanism of heat ICD at 104 °C for antigen diagnosis of heartworm. No significant change occurred in antigen detection following heat, chemical or enzymatic digestions supporting a heat-stable linear nature of the epitope.

Immunohistochemistry for acetylcholinesterase and butyrylcholinesterase in the dorsal motor nucleus of the vagus (DMNV) of formalin-fixed, paraffin-embedded tissue: comparison with reported literature

The majority of research regarding the expression of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in the brain has been conducted using histochemistry to identify enzymatic activity in frozen fixed tissue. However, retrospective human neurochemistry studies are generally restricted to formalin-fixed, paraffin-embedded (FFPE) tissues that are not suitable for histochemical procedures. The availability of commercially available antibody formulations provides the means to study such tissues by immunohistochemistry (IHC). In this study, we optimised IHC conditions for evaluating the expression of AChE and BuChE in the brainstem, focusing on the dorsal motor nucleus of the vagus, in human and piglet FFPE tissues, using commercially available antibodies. Our results were compared to published reports of histochemically determined AChE and BuChE expression. We varied antibody concentrations and antigen retrieval methods, and evaluated different detection systems, with the overall aim to optimise immunohistochemical staining. The primary findings, consistent across both species, are: (1) AChE and BuChE expression dominated in the neuronal somata, specifically in the neuronal cytoplasm; and (2) no change in the protocol resulted in axonal/neuropil expression of AChE. These results indicate that IHC is a suitable tool to detect AChE and BuChE in FFPE tissue using commercial antibodies, albeit the staining patterns obtained differed from those using histochemistry in frozen tissue. The underlying cause(s) for these differences are discussed in detail and may be associated with the principal components of the staining method, the antibody protein target and/or limitations to the detection of epitopes by tissue fixation.

Optimized protocol for MALDI MSI of N-glycans using an on-tissue digestion in fresh frozen tissue sections

Glycans play an important role in biology with multiple cellular functions ranging from cell signaling, mobility and growth to protein folding and localization. The N-glycosylation state within a tissue has been found to vary greatly between healthy and diseased patients and has proven to have an important clinical diagnostic value. Matrix assisted laser-desorption ionization (MALDI) mass spectrometry imaging (MSI) allows for untargeted analysis of biomolecules, including N-glycans, on a tissue section and provides a spatial context of the analyte. Until now, N-glycans have been predominantly analyzed using MALDI MSI on formalin-fixed paraffin embedded (FFPE) tissue sections, however this greatly reduces the clinical applicability, as the FFPE embedding process alters the biological environment of the tissue. Here we developed a protocol that allows for MALDI MSI of N-glycans from fresh frozen tissue that matches the current standard of FFPE analysis. By optimizing several steps in the sample preparation, we see orders of magnitude increase in signal intensity. Furthermore, this method limits delocalization of released N-glycans, thus improving the effective spatial resolution of the label-free molecular images. This protocol provides a novel perspective towards clinical application of MALDI MSI and capitalizes on the diagnostic value of N-glycan analysis.

Visualization of Small Intact Proteins in Breast Cancer FFPE Tissue

Molecular visualization of metabolites, lipids, and proteins by matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) is becoming an in-demand analytical approach to aid the histopathological analysis of breast cancer. Particularly, proteins seem to play a role in cancer progression, and specific proteins are currently used in the clinic for staging. Formalin-fixed paraffin-embedded (FFPE) tissues are ideal for correlating the molecular markers with clinical outcomes due to their long-term storage. So far, to obtain proteomic information by MSI from this kind of tissue, antigen retrieval and tryptic digestion steps are required. In this chapter, we present a protocol to spatially detect small proteins in tumor and necrotic regions of patient-derived breast cancer xenograft FFPE tissues without employing any on-tissue digestion. This protocol can be used for other kinds of FFPE tissue following specific optimization of the sample preparation phases.

Sympathetic innervation of human and porcine spleens: implications for between species variation in function

BACKGROUND

The vagus nerve affects innate immune responses by activating spleen-projecting sympathetic neurons, which modulate leukocyte function. Recent basic and clinical research investigating vagus nerve stimulation to engage the cholinergic anti-inflammatory pathway (CAP) has shown promising therapeutic results for a variety of inflammatory diseases. Abundant sympathetic innervation occurs in rodent spleens, and use of these species has dominated mechanistic research investigating the CAP. However, previous neuroanatomical studies of human spleen found a more restricted pattern of innervation compared to rodents. Therefore, our primary goal was to establish the full extent of sympathetic innervation of human spleens using donor tissue with the shortest procurement to fixation time. Parallel studies of porcine spleen, a large animal model, were performed as a positive control and for comparison.

METHODS

Human and porcine spleen tissue were fixed immediately after harvest and prepared for immunohistochemistry. Human heart and porcine spleen were stained in conjunction as positive controls. Several immunohistochemical protocols were compared for best results. Tissue was stained for tyrosine hydroxylase (TH), a noradrenergic marker, using VIP purple chromogen. Consecutive tissue slices were stained for neuropeptide Y (NPY), which often co-localizes with TH, or double-labelled for TH and CD3, a T cell marker. High-magnification images and full scans of the tissue were obtained and analyzed for qualitative differences between species.

RESULTS

TH had dominant perivascular localization in human spleen, with negligible innervation of parenchyma, but such nerves were abundant throughout ventricular myocardium. In marked contrast, noradrenergic innervation was abundant in all regions of porcine spleen, with red pulp having more nerves than white pulp. NPY stain results were consistent with this pattern. In human spleen, noradrenergic nerves only ran close to T cells at the boundary of the periarterial lymphatic sheath and arteries. In porcine spleen, noradrenergic nerves were closely associated with T cells in both white and red pulp as well as other leukocytes in red pulp.

CONCLUSION

Sympathetic innervation of the spleen varies between species in both distribution and abundance, with humans and pigs being at opposite extremes. This has important implications for sympathetic regulation of neuroimmune interactions in the spleen of different species and focused targeting of the CAP in humans.

Validation of Six Commercial Antibodies for the Detection of Heterologous and Endogenous TRPM8 Ion Channel Expression

TRPM8 is a non-selective cation channel expressed in primary sensory neurons and other tissues, including the prostate and urothelium. Its participation in different physiological and pathological processes such as thermoregulation, pain, itch, inflammation and cancer has been widely described, making it a promising target for therapeutic approaches. The detection and quantification of TRPM8 seems crucial for advancing the knowledge of the mechanisms underlying its role in these pathophysiological conditions. Antibody-based techniques are commonly used for protein detection and quantification, although their performance with many ion channels, including TRPM8, is suboptimal. Thus, the search for reliable antibodies is of utmost importance. In this study, we characterized the performance of six TRPM8 commercial antibodies in three immunodetection techniques: Western blot, immunocytochemistry and immunohistochemistry. Different outcomes were obtained for the tested antibodies; two of them proved to be successful in detecting TRPM8 in the three approaches while, in the conditions tested, the other four were acceptable only for specific techniques. Considering our results, we offer some insight into the usefulness of these antibodies for the detection of TRPM8 depending on the methodology of choice.

Immunohistochemical Detection of Estrogen Receptor-Beta (ERβ) with PPZ0506 Antibody in Murine Tissue: From Pitfalls to Optimization

The estrogen receptor beta (ERβ) is physiologically essential for reproductive biology and is implicated in various diseases. However, despite more than 20 years of intensive research on ERβ, there are still uncertainties about its distribution in tissues and cellular expression. Several studies show contrasts between mRNA and protein levels, and the use of knockout strategies revealed that many commercially available antibodies gave false-positive expression results. Recently, a specific monoclonal antibody against human ERβ (PPZ0506) showed cross-reactivity with rodents and was optimized for the detection of rat ERβ. Herein, we established an immunohistochemical detection protocol for ERβ protein in mouse tissue. Staining was optimized on murine ovaries, as granulosa cells are known to strongly express ERβ. The staining results were confirmed by western blot analysis and RT-PCR. To obtain accurate and reliable staining results, different staining conditions were tested in paraffin-embedded tissues. Different pitfalls were encountered in immunohistochemical detection. Strong heat-induced epitope retrieval (HIER) and appropriate antibody dilution were required to visualize specific nuclear expression of ERβ. Finally, the specificity of the antibody was confirmed by using ovaries from Esr2-depleted mice. However, in some animals, strong (non-specific) background staining appeared. These signals could not be significantly alleviated with commercially available additional blocking solutions and are most likely due to estrus-dependent expression of endogenous immunoglobulins. In summary, our study showed that the antibody PPZ0506, originally directed against human ERβ, is also suitable for reliable detection of murine ERβ. An established staining protocol mitigated ambiguities regarding the expression and distribution of ERβ in different tissues and will contribute to an improved understanding of its role and functions in murine tissues in the future.

Standardization of Manual Method of Immunohistochemical Staining for Breast Cancer Biomarkers at Tertiary Cancer Care Center: An Audit

Immunohistochemistry (IHC) is a necessary ancillary technique in surgical pathology laboratories, particularly for oncology tissue specimens. Automation in the IHC technique has an advantage over manual methods in terms of quality, except for the cost of the equipment. Thus, the manual method of IHC staining is the preferred method of choice in countries with limited resources. However, standardization of all steps in the preanalytic phase is critical to obtain reliable immunohistochemistry test results. The current audit was conducted to describe the preanalytic factors affecting manual IHC methods. The most important preanalytic factors were fixative, the composition of dehydrate, pH, drying of sections, and heat-mediated antigen retrieval method (HMAR). The domestic pressure cooker method was found to be the best for HMAR.

Tissue sample preparations for preclinical research determined by molecular imaging mass spectrometry using MALDI

Matrix-assisted laser desorption/ionization - imaging mass spectrometry is an alternative tool, which can be implemented in order to obtain and visualize the "omic" signature of tissue samples. Its application to clinical study enables simultaneous imaging-based morphological observations and mass spectrometry analysis. Application of fully informative material like tissue, allows to obtain the complex and unique profile of analyzed samples. This knowledge leads to diagnose disease, study the mechanism of cancer development, select the potential biomarkers as well as correlating obtained image with prognosis. Nevertheless, it is worth to notice that this method is found to be objective but the result of analysis is mainly influenced by the sample preparation protocol, included collection of biological material, its preservation and processing. However, application of this approach requires a special sample preparation procedure. The main goal of the study is to present the current knowledge on the clinical application of matrix-assisted laser desorption/ionization - imaging mass spectrometry in cancer research, with particular emphasis on the sample preparation step. For this purpose, several protocols based on cryosections and formalin-fixed paraffin embedded tissue were compiled and compared, taking into account the measured metabolites of potential diagnostic importance for a given type of cancer. This article is protected by copyright. All rights reserved.

Antigen Retrieval and Signal Amplification

Immunohistochemistry (IHC) offers a valuable method for determining the spatial distribution of proteins in cells and tissues. Fixation of tissues prior IHC enables their long-term stability and preserves tissue morphology; however, downstream analysis of protein localization within fixed samples can be complicated by cross-links formed between proteins during formalin fixation which mask target epitopes. Antigen Retrieval (AR) is a process introduced to reverse such cross-links, improving the sensitivity of antibody-based protein detection, and can be performed using protease- or heat-based approaches. Even following AR, low abundance target proteins may require additional amplification for sensitive visualization. The development of amplification approaches such as the use of biotinylated secondary antibodies with avidin-biotin complex and tyramide signal amplification greatly improve the sensitivity of IHC, enabling a wider range of epitopes to be detected when coupled with AR.

Interrogating the Tumor Microenvironment by Deep Tissue Immunoprofiling

With the modern success of immunotherapy from chimeric antigen receptor T-cell therapy to checkpoint blockade, an understanding of the tumor microenvironment has been more essential than ever. Knowing the key immune players in the tumor can provide the basis for studying cancer host immunity and interactions governing tumor tolerance. This endeavor can be approached in a step like manner-from a broad overview with immunohistochemistry to genomic expression analysis, followed by detailed functional analysis of each cell with multiparameter flow cytometry.

Thickening of Ectatic Cornea through Regeneration Using Decellularized Corneal Matrix Injectable Hydrogel: A Strategic Advancement to Mitigate Corneal Ectasia

Ectatic corneal diseases are a group of eye disorders characterized by progressive thinning and outward bulging of the cornea, resulting in vision impairment. A few attempts have been made to use cornea-derived extracellular matrix hydrogels for corneal tissue engineering; however, no studies have investigated its application in corneal ectasia. In this study, we have first developed an animal surgical model that mimics a few specific phenotypes of ectatic cornea. Later, we investigated the potential of decellularized cornea matrix hydrogels (dCMH) from both human and bovine sources in increasing the thickness of the cornea in the developed surgical model. Our data advocate that surgical stromal depletion can be followed to establish ectatic models and can also provide information on the biocompatibility of materials, its integration with native stroma, degradation over time, and tissue remodeling. We observed that dCMH from both sources could integrate with ectatic thin corneal stroma and helps in regaining the thickness by regenerating a reasonably functional and transparent stroma; however, no significant difference was spotted between the dCMH made from human and bovine corneal tissue sources. Hence, this study is a promising step toward developing a non-invasive technique for the treatment of corneal ectasia by using dCMH.

Protocol for cryoinjury model in neonatal mice for heart regeneration and repair research

The variability of animal experimental groups and high maternal cannibalization are two major limitations in cardiac injury models. A cryoinjury model could be an ideal model in heart regeneration and repair research as it can provide reproducible results and the injury size can be scaled. Here, we describe a simple and successful cryoinjury model (rate of mouse survival >90% and rate of maternal cannibalization <5%) for evaluating heart injury in regenerating and non-regenerating mice. For complete details on the use and execution of this protocol, please refer to Zhao et al. (2021).

Retinal Spheroids and Axon Pathology Identified in Amyotrophic Lateral Sclerosis

Purpose

To determine whether patients with amyotrophic lateral sclerosis (ALS) show retinal axon pathology.

Methods

Postmortem eyes from 10 patients with ALS were sectioned and compared with 10 age-matched controls. Retinal sections were evaluated with periodic acid Schiff and phosphorylated (P-NF) and nonphosphorylated (NP-NF) forms of neurofilament with SMI 31 and 32 antibodies. Spheroids identified in the retinal nerve fiber layer were counted and their overall density was calculated in central, peripheral, and peripapillary regions. P-NF intensity was quantified. Morphometric features of ALS cases were compared with age-matched controls using the exact Wilcoxon matched-pairs signed-rank test.

Results

Distinct periodic acid Schiff–positive round profiles were identified in the retinal nerve fiber layer of patients with ALS and were most commonly observed in the peripapillary and peripheral retina. The density of periodic acid Schiff–positive spheroids was significantly greater in patients with ALS compared with controls (P = 0.027), with increased density in the peripapillary region (P = 0.047). Spheroids positive for P-NF and NP-NF were detected. P-NF–positive spheroid density was significantly increased in patients with ALS (P = 0.004), while the density of NP-NF spheroids did not differ significantly between ALS and control groups (P > 0.05). P-NF immunoreactivity in the retinal nerve fiber layer was significantly greater in patients with ALS than in controls (P = 0.002).

Conclusions

Retinal spheroids and axon pathology discovered in patients with ALS, similar to hallmark findings in spinal cord motor neurons, point to disrupted axon transport as a shared pathogenesis. Retinal manifestations detected in ALS suggest a novel biomarker detectable by noninvasive retinal imaging to help to diagnose and monitor ALS disease.

Urinary prostaglandin E2 as a biomarker for recurrent UTI in postmenopausal women

This work uses controlled human cohorts to investigate urinary prostaglandin E2, the product of cyclooxygenase-2, as both a diagnostic and prognostic biomarker of recurrent UTI postmenopausal women.

Urinary tract infection (UTI) is one of the most common adult bacterial infections and exhibits high recurrence rates, especially in postmenopausal women. Studies in mouse models suggest that cyclooxygenase-2 (COX-2)–mediated inflammation sensitizes the bladder to recurrent UTI (rUTI). However, COX-2–mediated inflammation has not been robustly studied in human rUTI. We used human cohorts to assess urothelial COX-2 production and evaluate its product, PGE₂, as a biomarker for rUTI in postmenopausal women. We found that the percentage of COX-2–positive cells was elevated in inflamed versus uninflamed bladder regions. We analyzed the performance of urinary PGE₂ as a biomarker for rUTI in a controlled cohort of 92 postmenopausal women and PGE₂ consistently outperformed all other tested clinical variables as a predictor of rUTI status. Furthermore, time-to-relapse analysis indicated that the risk of rUTI relapse was 3.6 times higher in women with above median urinary PGE₂ levels than with below median levels. Taken together, these data suggest that urinary PGE₂ may be a clinically useful diagnostic and prognostic biomarker for rUTI in postmenopausal women.

Mechanical Compression of Coverslipped Tissue Sections During Heat-induced Antigen Retrieval Prevents Section Detachment and Preserves Tissue Morphology

Heat-induced antigen retrieval (HIAR) is routinely employed on aldehyde-fixed tissue sections to enhance the reactivity of antibodies that exhibit weak or no specific interactions with tissue antigens when applied in conventional immunohistochemical protocols. A major drawback of HIAR protocols is, however, the heat-induced detachment of sections from the microscope slide with resultant impaired tissue morphology or loss of the section. We developed a method in which tissue sections mounted on glass slides are temporally coverslipped, and a clamp is used to compress the sections on the microscope slide during HIAR treatment. This "pressurized coverslipping" during HIAR was tested on various formalin-fixed tissues (murine kidneys and temporal bones, human tonsils and temporal bones) that were embedded in paraffin or celloidin. The method reliably kept the sections adherent to the slide, preserved the tissue morphology, and effectively retrieved tissue antigens for improved results in immunohistochemical labeling, even for exceptionally delicate, large, and poorly adhering sections, that is, decalcified human temporal bone sections. In summary, we present a simple method for improved slide adherence and morphological preservation of tissue sections during HIAR treatment that can be combined with all HIAR protocols and that requires only basic lab equipment.

Immunohistochemistry in Investigative and Toxicologic Pathology

Immunohistochemistry (IHC) is a valuable tool in pathology. This review provides a brief description of the technical aspects of IHC and a detailed discussion on the variables that affect the results, interpretation, and reproducibility of IHC results. Lists of antibodies that have and have not worked in IHC on various mouse and rat tissues in our laboratory are provided as a guidance for selection of antibodies. An approach to IHC method optimization is presented. Finally, the critical information that should be included as a part of peer-reviewed manuscript is also discussed.

E-cadherin and ZEB2 modulate trophoblast cell differentiation during placental development in pigs

It is one of the important events that trophoblast cells within the placental folds differentiate into two types that differ in cell shape during placental development in pigs. This study showed that all the trophoblast cells were of similar shape between Yorkshire and Chinese Meishan pigs on day 26 of gestation; thereafter, the trophoblast cells located at the top of the placental folds became high columnar, while those cells at the base of the placental folds were cuboidal on day 50 of gestation. Additionally, on day 95 of gestation, all the trophoblast cells in Meishan pigs became cuboidal, but the trophoblast cells located at the top of the placental folds in Yorkshire pigs still remained columnar. The membranous E-cadherin and β-catenin were strongly co-expressed by the high columnar trophoblast cells but very weakly expressed by those cuboidal cells. Consistently, the expression pattern of ZEB2, the E-cadherin repressor, was inversely correlated with that of E-cadherin in the two types of trophoblast cells in the two breeds. Furthermore, electrophoretic mobility shift assays demonstrated the binding of ZEB2 to the E-cadherin promoter in nuclear extracts from porcine placental tissue. These findings suggest a ZEB2-dependent mechanism of trophoblast cell differentiation during placental development in pigs.

Immune signatures of pathogenesis in the peritoneal compartment during early infection of sheep with Fasciola hepatica

Immune signatures of sheep acutely-infected with Fasciola hepatica, an important pathogen of livestock and humans were analysed within the peritoneal compartment to investigate early infection. Within the peritoneum, F. hepatica antibodies coincided with an intense innate and adaptive cellular immune response, with infiltrating leukocytes and a marked eosinophilia (49%). However, while cytokine qPCR analysis revealed IL-10, IL-12, IL-13, IL-23 and TGFβ were elevated, these were not statistically different at 18 days post-infection compared to uninfected animals indicating that the immune response is muted and not yet skewed to a Th2 type response that is associated with chronic disease. Proteomic analysis of the peritoneal fluid identified infection-related proteins, including several structural proteins derived from the liver extracellular matrix, connective tissue and epithelium, and proteins related to the immune system. Periostin and vascular cell adhesion protein 1 (VCAM-1), molecules that mediate leukocyte infiltration and are associated with inflammatory disorders involving marked eosinophilia (e.g. asthma), were particularly elevated in the peritoneum. Immuno-histochemical studies indicated that the source of periostin and VCAM-1 was the inflamed sheep liver tissue. This study has revealed previously unknown aspects of the immunology and pathogenesis associated with acute fascioliasis in the peritoneum and liver.

Immunohistochemistry for the detection of neural and inflammatory cells in equine brain tissue

Phenotypic characterization of cellular responses in equine infectious encephalitides has had limited description of both peripheral and resident cell populations in central nervous system (CNS) tissues due to limited species-specific reagents that react with formalin-fixed, paraffin embedded tissue (FFPE). This study identified a set of antibodies for investigating the immunopathology of infectious CNS diseases in horses. Multiple commercially available staining reagents and antibodies derived from antigens of various species for manual immunohistochemistry (IHC) were screened. Several techniques and reagents for heat-induced antigen retrieval, non-specific protein blocking, endogenous peroxidase blocking, and visualization-detection systems were tested during IHC protocol development. Boiling of slides in a low pH, citrate-based buffer solution in a double-boiler system was most consistent for epitope retrieval. Pressure-cooking, microwaving, high pH buffers, and proteinase K solutions often resulted in tissue disruption or no reactivity. Optimal blocking reagents and concentrations of each working antibody were determined. Ultimately, a set of monoclonal (mAb) and polyclonal antibodies (pAb) were identified for CD3⁺ (pAb A0452, Dako) T-lymphocytes, CD79αcy⁺ B-lymphocytes (mAb HM57, Dako), macrophages (mAb MAC387, Leica), NF-H⁺ neurons (mAb NAP4, EnCor Biotechnology), microglia/macrophage (pAb Iba-1, Wako), and GFAP⁺ astrocytes (mAb 5C10, EnCor Biotechnology). In paraffin embedded tissues, mAbs and pAbs derived from human and swine antigens were very successful at binding equine tissue targets. Individual, optimized protocols are provided for each positively reactive antibody for analyzing equine neuroinflammatory disease histopathology.

Characterization of discrete equine intestinal epithelial cell lineages

OBJECTIVE

To characterize epithelial cells of the small intestine and colon in horses without clinical gastrointestinal abnormalities with an emphasis on the stem cell niche constituents.

SAMPLE

Mucosal biopsy specimens from small and large intestines obtained from 12 horses euthanized for reasons unrelated to gastrointestinal disease or systemic disease.

PROCEDURES

Intestinal biopsy specimens were collected by sharp dissection immediately following euthanasia. Specimens were prepared for immunohistochemical, immunofluorescence, and transmission electron microscopic imaging to detect and characterize each epithelial cell type. Antibodies against protein biomarkers for cellular identification were selected on the basis of expression in other mammalian species.

RESULTS

Intestinal epithelial cell types were identified by means of immunostaining and morphological characterization with transmission electron microscopy. Some differences in biomarker expression and antibody cross-reactivity were identified in equine tissue, compared with other species. However, each known type of mucosal epithelial cell was identified in equine tissue.

CONCLUSIONS AND CLINICAL RELEVANCE

The methodology used can enhance detection of stem cells and progenitor cells as well as postmitotic cell lineages in equine intestinal tissues. Results may have relevance to regenerative potential of intestinal mucosa and survival in horses with colic.

Identification of 5-bromo-2'-deoxyuridine-labeled cells during mouse spermatogenesis by heat-induced antigen retrieval in lectin staining and immunohistochemistry

DNA replication occurs during S-phase in spermatogonia and preleptotene spermatocytes during spermatogenesis. 5-Bromo-2'-deoxyuridine (BrdU) is incorporated into synthesized DNA and is detectable in the nucleus by immunohistochemistry (IHC). To identify BrdU-labeled spermatogenic cells, the spermatogenic stages must be determined by visualizing acrosomes and detecting cell type-specific marker molecules in the seminiferous tubules. However, the antibody reaction with BrdU routinely requires denaturation of the DNA, which is achieved by pretreating tissue sections with hydrochloric acid; however, this commonly interferes with further histochemical approaches. Therefore, we examined optimal methods for pretreating paraffin sections of the mouse testis to detect incorporated BrdU by an antibody and, at the same time, visualize acrosomes with peanut agglutinin (PNA) or detect several marker molecules with antibodies. We found that the use of heat-induced antigen retrieval (HIAR), which consisted of heating at 95C in 20 mM Tris-HCl buffer (pH 9.0) for 15 min, was superior to the use of 2 N hydrochloric acid for 90 min at room temperature in terms of the quality of subsequent PNA-lectin histochemistry with double IHC for BrdU and an appropriate stage marker protein. With this method, we identified BrdU-labeled spermatogenic cells during mouse spermatogenesis as A1 spermatogonia through to preleptotene spermatocytes.

Immunofluorescence staining with frozen mouse or chick embryonic tissue sections

Immunofluorescence (IF), a form of immunohistochemistry (IHC) with specific applications, is commonly used for both basic research and clinical studies, including diagnostics, and involves visualizing the cellular distribution of target molecules (e.g., proteins, DNA, and small molecules) using a microscope capable of exciting and detecting fluorochrome compounds that emit light at specific, largely nonoverlapping wavelengths. The procedure for carrying out IF varies according to the tissue type and methods for processing and preparing tissue (e.g., fixative used to preserve tissue morphology and antigenicity). The protocol presented here provides a general guideline for multichannel IF staining using frozen embryonic mouse or chicken tissue sectioned on a cryostat. In general, the procedure involves the following: (1) fixing freshly dissected tissues in a 4 % paraformaldehyde solution buffered in the physiological pH range, (2) cryopreservation of tissue in a 30 % sucrose solution, (3) embedding and sectioning tissue in Optimal Cutting Temperature (OCT) matrix compound, (4) direct or indirect detection of the target antigen/s using fluorochrome-conjugated antibodies.

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.

Optimization of immunolocalization of cell cycle proteins in human corneal endothelial cells

PURPOSE

En face observation of corneal endothelial cells (ECs) using flat-mounted whole corneas is theoretically much more informative than observation of cross-sections that show only a few cells. Nevertheless, it is not widespread for immunolocalization (IL) of proteins, probably because the endothelium, a superficial monolayer, behaves neither like a tissue in immunohistochemistry (IHC) nor like a cell culture in immunocytochemistry (ICC). In our study we optimized IL for ECs of flat-mounted human corneas to study the expression of cell cycle-related proteins.

METHODS

We systematically screened 15 fixation and five antigen retrieval (AR) methods on 118 human fresh or stored corneas (organ culture at 31 °C), followed by conventional immunofluorescence labeling. First, in an attempt to define a universal protocol, we selected combinations able to correctly localize four proteins that are perfectly defined in ECs (zonula occludens-1 [ZO-1] and actin) or ubiquitous (heterogeneous nuclear ribonucleoprotein L [hnRNP L] and histone H3). Second, we screened protocols adapted to the revelation of 9 cell cycle proteins: Ki67, proliferating cell nuclear antigen (PCNA), minichromosome maintenance protein 2 (MCM2), cyclin D1, cyclin E, cyclin A, p16(Ink4a), p21(Cip1) and p27(Kip1). Primary antibody controls (positive controls) were performed on both epithelial cells of the same, simultaneously-stained whole corneas, and by ICC on human ECs in in vitro non-confluent cultures. Both controls are known to contain proliferating cells. IL efficiency was evaluated by two observers in a masked fashion. Correct localization at optical microscopy level in ECs was define as clear labeling with no background, homogeneous staining, agreement with previous works on ECs and/or protein functions, as well as a meaningful IL in proliferating cells of both controls.

RESULTS

The common fixation with 4% formaldehyde (gold standard for IHC) failed to reveal 12 of the 13 proteins. In contrast, they were all revealed using either 0.5% formaldehyde at room temperature (RT) during 30 min alone or followed by AR with sodium dodecyl sulfate or trypsin, or pure methanol for 30 min at RT. Individual optimization was nevertheless often required to optimize the labeling. Ki67 was absent in both fresh and stored corneas, whereas PCNA was found in the nucleus, and MCM2 in the cytoplasm, of all ECs. Cyclin D1 was found in the cytoplasm in a paranuclear pattern much more visible after corneal storage. Cyclin E and cyclin A were respectively nuclear and cytoplasmic, unmodified by storage. P21 was not found in ECs with three different antibodies. P16 and p27 were exclusively nuclear, unmodified by storage.

CONCLUSIONS

IL in ECs of flat-mounted whole human corneas requires a specific sample preparation, especially to avoid overfixation with aldehydes that probably easily masks epitopes. En face observation allows easy analysis of labeling pattern within the endothelial layer and clear subcellular localization, neither of which had previously been described for PCNA, MCM2, or cyclin D1.

Analysis of pluripotent stem cells by using cryosections of embryoid bodies

Embryonic stem (ES) cells are pluripotent cells derived from the inner cell mass of blastocyst-stage early mammalian embryos. A crucial stage in the differentiation of ES cells is the formation of embryoid bodies (EBs) aggregates. EB formation is based on spontaneous aggregation when ES cells are cultured in non adherent plates. Three-dimensional EB recapitulates many aspects of early mammalian embryogenesis and differentiate into the three germ layers: ectoderm, mesoderm and endoderm. Immunofluorescence and in situ hybridization are widely used techniques for the detection of target proteins and mRNA present in cells of a tissue section. Here we present a simple technique to generate high quality cryosections of embryoid bodies. This approach relies on the spatial orientation of EB embedding in OCT followed by the cryosection technique. The resulting sections can be subjected to a wide variety of analytical procedures in order to characterize populations of cells containing certain proteins, RNA or DNA. In this sense, the preparation of EB cryosections (10 μm) are essential tools for histology staining analysis (e.g. Hematoxilin and Eosin, DAPI), immunofluorescence (e.g. Oct4, nestin) or in situ hybridization. This technique can also help to understand aspects of embryogenesis with regards to the maintenance of the tri-dimensional spherical structure of EBs.