Section Immunostaining for Protein Expression and Cell Proliferation Studies of Regenerating Fins

Adult zebrafish fins fully regenerate after resection, providing a highly accessible and remarkable vertebrate model of organ regeneration. Fin injury triggers wound epidermis formation and the dedifferentiation of injury-adjacent mature cells to establish an organized blastema of progenitor cells. Balanced cell proliferation and redifferentiation along with cell movements then progressively reestablish patterned tissues and restore the fin to its original size and shape. A mechanistic understanding of these coordinated cell behaviors and transitions requires direct knowledge of proteins in their physiological context, including expression, subcellular localization, and activity. Antibody-based staining of sectioned fins facilitates such high-resolution analyses of specific, native proteins. Therefore, such methods are mainstays of comprehensive, hypothesis-driven fin regeneration studies. However, section immunostaining requires labor-intensive, empirical optimization. Here, we present detailed, multistep procedures for antibody staining and co-detecting proliferating cells using paraffin and frozen fin sections. We include suggestions to avoid common pitfalls and to streamline the development of optimized, validated protocols for new and challenging antibodies.

Effect of storage time of paraffin sections on the expression of PD-L1 (SP142) in invasive breast cancer

BACKGROUND

PD-L1 staining using long-stored paraffin sections may not be consistent with the true PD-L1 expression of patients. Therefore, it is necessary to explore the expression of PD-L1(SP142) in paraffin sections of invasive breast cancer with different storage times and the optimal storage temperature for unstained paraffin sections.

METHODS

The study included 71 cases of PD-L1(SP142) positive breast cancer. The unstained paraffin sections were stored at room temperature conditions (20-25 °C), 4 °C, -20 °C and - 80 °C, respectively. PD-L1 staining was performed at 1, 2, 3, 4, 8, 12 and 24 weeks of storage. PD-L1 expression was assessed with a continuity score.

RESULTS

The PD-L1 antigen was gradually lost as the storage time of paraffin sections increased. The PD-L1 positivity rate was 97.18% at 1 week for the sections stored at room temperature, and decreased from 83.10 to 71.83% for the sections stored for 2 weeks to 4 weeks, and 61.97%, 54.93%, and 32.93% for 8, 12, and 24 weeks, respectively. When stored at low temperatures of 4 °C, -20 °C and - 80 °C, the positivity rate decreases with the same trend but more slowly compared to room temperature. The mean IC score of PD-L1 also showed a gradual decrease in all cases. In the consistency analysis, PD-L1 expression in slices stored at room temperature for 2 weeks was consistent with PD-L1 expression in fresh slices (ICC ≥ 0.9 for all slices), and PD-L1 expression in slices stored at 4 °C or -20 °C for 4 weeks was consistent with PD-L1 expression in fresh slices (ICC ≥ 0.9 for all slices). When stored under refrigeration at -80 °C, PD-L1 expression in slices stored for 3 weeks was consistent with that in fresh slices (ICC ≥ 0.9).

CONCLUSIONS

To our knowledge, this is the first article on the effect of preservation time and preservation temperature of paraffin sections on PD-L1 expression in breast cancer. Long-term storage of paraffin sections of unstained invasive breast cancer can lead to antigen loss of PD-L1 (SP142). Refrigerated storage of paraffin sections can delay antigen loss, with best results at 4 °C or -20 °C, and a storage time of no more than 4 weeks is recommended.

Combined Lectin- and Immuno-histochemistry (CLIH) for Fluorescence Microscopy

The function of glycoproteins depends both on their polypeptide chain and sugar residues. For detection and localization of glycoproteins in tissue sections, methods of immunohistochemistry (IHC) and lectin histochemistry (LHC) are usually used separately. For a better understanding of the expression and distribution of variants of glycoproteins, tissue sections can be analyzed by combined lectin- and immuno-histochemistry (CLIH). CLIH exploits the advantages of both IHC and LHC and can therefore contribute to research in glycobiology and other fields of cell biology. Since cancer transformation is accompanied by alterations in the glycosylation of some glycoproteins, CLIH could also be exploited for improved classification of cancers. The chapter considers how CLIH could be employed on paraffin sections and semithin cryosections for fluorescence microscopy. Five different protocols of CLIH are described in detail as well as appropriate negative controls.

TUNEL Staining in Sections of Paraffin-Enabled Planarians

Planarians are a model animal for the study of regeneration and homeostasis. Understanding how planarians control their cellular balance is key to the knowledge of their plasticity. Both apoptotic and mitotic rates can be quantified in "whole mount" planarians. Apoptosis is usually analyzed through terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), a technique that detects cell death by identifying DNA breaks. In this chapter we detail a protocol to analyze apoptotic cells in paraffin sections of planarians, which enables a more accurate cellular visualization and quantification than in "whole mount."

Histochemical detection of free thiols in glandular cells and tissues of different marine Polychaeta

Either through differentiated glands or specialised individual cells, the coating epithelia of soft-bodied marine invertebrates are responsible for the secretion of a broad span of peptidic substances, from protective mucins to biocides. These secretions are characterised by the presence of cysteine-rich proteins and peptides, rendering a distinct histochemical signature of secretory epithelia. Through a histochemical procedure for fluorescence microscopy in paraffin sections, we performed a comparative assessment of the distribution of thiol-rich compounds in multiple epithelia of different species of intertidal Polychaeta, which revealed distinctive patterns of distribution that closely relate to ecology, morphoanatomy and physiology. The presence of free thiols was notorious in mucocytes and enzyme-plus toxin-secreting cells. Consequently, strong signals were recorded in the mucocytes of the parapodia of Nereis splendida, the epidermis and pharynx epithelium of Mysta picta and the venom glands of Glycera alba. The findings show an investment in mucus secretion in foragers such as Nereis and Mysta, especially the latter, which is not a native burrower, as a protective response and as lubricant for locomotion. Additionally, nereidids are believed to secret integumentary toxins for defence. On the other hand, Glycera is an ambush predatorial burrower whose behaviour entirely revolves around the delivery of venom making use of its four jaws. The results showed that the detection of thiol-rich compounds in histological sections can be a tool to identify potential toxin secretion and delivery structures, with important consequences for the bioprospecting of novel bioreactives from marine invertebrates for the purpose of drug discovery.

Tissue expansion of lung bronchi due to tissue processing for histology - A comparative analysis of paraffin versus frozen sections in a pig model

AIM

Tissue shrinking due to fixation and processing is well known. However, the degree of shrinking varies significantly with the tissue type as well as the processing method and is not well studied in various tissues. In daily pathological routine workflow, histological specimens from frozen and paraffin sections are performed from the same tissue. In the present study we compared the thickness of bronchus walls obtained from paraffin and frozen sections.

METHODS

Pig lungs were frozen in ventilated condition in liquid nitrogen and 36 bronchi were isolated after dissection. Frozen sections of 5 μm thickness were performed and the remaining tissue was fixed and embedded in paraffin after fixation in 4% formalin. Frozen and paraffin sections from the same cutting edge were analysed after haematoxylin and eosin staining by measuring the wall thickness of the bronchi using high power fields of 400-fold magnification. In each bronchus 40 measurements were implemented at different wall positions distributed over the entire wall area. Summed up, in each group 1440 wall measurements were performed in total. Statistical analysis was conducted using the Wilcoxon test and t-test as well as Pearson's correlation coefficient with a significance level at P < 0.05.

RESULTS

The bronchial wall thickness was significantly (p < 0.001) smaller in frozen sections (median: 0.50 mm; min: 0.37 mm; max: 0.97 mm) compared to paraffin sections (median: 0.58 mm; min: 0.35 mm; max: 1.06 mm). The median difference between paraffin and frozen sections was 0.05 mm (min: -0.11 mm; max: 0.22 mm). The wall thickness ratio of both groups was as follows: frozen/paraffin section = 0.8609, thus yielding a difference between paraffin and frozen of 13.91%. High correlation was found between wall thickness measurements on paraffin and frozen sections (R = 0.87, p < 0.001).

CONCLUSIONS

The bronchus wall thickness in the frozen section was 14% reduced compared to the paraffin section. In routine pathology as well as in scientific studies these results are of relevance, as airway wall thickness represents a relevant marker for pathological interpretation, especially using CT image techniques.

Methods for In Situ Protein Visualization in Dental Mineralized Tissues

Immunohistochemistry (IHC) is a technique based on the specificity of antibody-antigen principle used commonly to detect antigens in tissue sections. The immune labeling can be performed in paraffin sections, cryostat sections, and ultrathin sections and can be observed in light confocal and transmission electron microscopy. However, the use of immunohistochemical techniques for the study of mineralized tissues has been a challenge for decades (Berdal et al., Arch Oral Biol 36:715-725, 1991; Nanci et al., Eur J Histochem 52:201-214, 2008). Specific procedures are necessary when compared with soft tissue immunohistochemistry. This chapter describes methods for IHC on Tissue-Tek O.C.T. compound and paraffin-embedded sections to detect antigens in the dental mineralized tissues.

Microtomy: Cutting Formalin-Fixed, Paraffin-Embedded Sections

Formalin-fixed, paraffin-embedded tissue (FFPE) still plays an important role in biobanking, since it is comparatively easy to obtain and store in comparison to fresh frozen tissue. They are stored as paraffin or FFPE blocks. Unstained slides derived from FFPE blocks may be used for hematoxylin and eosin histology, special stains, immunohistochemistry, and chromogenic or fluorescent in situ hybridization. In addition, tissue scraped off FFPE slides or from scrolls of FFPE tissue may be used for molecular or proteomic analyses. Hematoxylin and eosin staining of FFPE sections reviewed by a pathologist are highly valuable to ensure the presence of adequate lesional cells for molecular and other analyses. Therefore, proper microtomy technique is essential in the preparation of formalin-fixed, paraffin-embedded tissue for biobanking purposes. Here we describe the process of cutting paraffin embedded sections using a rotary microtome. We also highlight the possible pitfalls that may arise and discuss how to avoid them.

3D approach visualizing cellular networks in human lymph nodes

Lymph node diagnostics are essentially based on cutting thin sections of formalin fixed tissues. After hematoxylin and eosin stain, Giemsa stain and immunohistochemical staining of these tissues, the lymph node diagnosis is done using a light microscope, looking at two-dimensional pictures. Three-dimensional visualizations of lymph node tissue have not been used in lymphoma diagnostics yet. This article describes three-dimensional visualization of lymphoid tissue, using thick paraffin sections, immunostained with monoclonal antibodies, confocal laser scanning and data processing with appropriate software and the 3D printing process itself. The advantages and disadvantages of different printing techniques are discussed as well as the application of 3D models in diagnostics, teaching and research of lymph nodes.

RNA In Situ Hybridization on Planarian Paraffin Sections

RNA in situ hybridization techniques are an important tool for the study of gene expression patterns in freshwater planarians. Here I describe a RNA in situ hybridization method on histological paraffin sections of planarian tissue. This protocol allows the visualization of gene expression at cellular or subcellular resolution. Following paraffin-embedding and sectioning of planarians, the resulting sections are hybridized with hapten-labeled RNA probes. Subsequent immunological probe detection is carried out with either chromogenic or fluorescent development. This protocol can be performed alone, or in combination with other immunodetection techniques, and represents a useful alternative to whole-mount protocols more commonly used in the community.

Development of a method for the detection of polystyrene microplastics in paraffin-embedded histological sections

The concerns about the presence of microplastics (MPs) in marine ecosystems have widely increased in the past years. This is reflected in a growing number of studies addressing the effects of exposure to these materials in indigenous, farmed and even laboratory marine animals subjected to toxicity-oriented bioassays. There have been, however, many constraints in the detection of MPs in biological tissues, as routine histological techniques tend to degrade these materials, which are especially sensitive to organic solvents. This issue hinders the application of standard histopathological procedures based on convenient paraffin wax-embedding protocols, with consequences for biomonitoring and bioassay procedures. The method described here was developed and validated for the detection of polystyrene microplastics in biological tissue processed for paraffin-based histology. The strategy was developed and tested from whole-soft body sections of marine mussels that internalised the MPs following dedicated bioassays. The protocol is based on the replacement of xylenes with isopropanol for the purpose of intermediate infiltration and deparaffinization. Special modifications for staining, mounting and archiving are needed and are detailed as well. The protocol is shown to be a highly cost- and time-effective procedure compatible with formalin-based fixatives plus standard sectioning and staining, yielding complete preservation of MPs and optimal tissue conditioning. The method also produced excellent results with pre-stained MPs, with fluorochromes included, altogether providing excellent localisation of polystyrene MPs in paraffin-processed biological tissue.

How to obtain good morphology and antigen detection in the same tissue section?

Most human and animal biopsy samples are routinely embedded in paraffin since this enables the pathologist or researcher to obtain excellent morphology and simplifies storage. Nevertheless, in many cases, the antigen of interest cannot be detected in paraffin section. The alternative available for good immunohistochemistry is preparation of cryosections, which usually provide decent antigen preservation and are frequently used for immunofluorescence. However, cryosections often do not provide efficient morphological details of tissues and cells for pathologic evaluation. In order to obtain good antigen preservation and improve tissue and cell morphology after freezing, we tested three different fixations and freezing methodologies and compared them to routine formaldehyde fixation and paraffin embedding. As a model system, we selected the epithelium of the rat urinary bladder and trachea. On all samples, haematoxylin and eosin staining was performed as well as immunofluorescence with antibodies against tight junction protein ZO-1 and against intermediate filament cytokeratin 7. The best compromise between morphology and immunofluorescence was obtained with "sucrose impregnation prior to freezing" method. Moreover, this procedure is also quicker in comparison to standard paraffin section preparation. To check the clinical relevance of our study, this method was used for human biopsy samples of neoplastic urothelial and bronchial mucosa lesions. Besides good immunofluorescence results, the morphology of these samples was well preserved. We therefore propose that cryosection preparation with sucrose impregnation prior to freezing should be further exploited in other clinical and veterinary applications, since it enables good morphology and antigen preservation.

Immunohistochemistry of Paraffin Sections from Mouse Ovaries

Immunohistochemistry (IHC) is an efficient technique to detect cellular localizations of the proteins in paraffin-embedded tissues. It allows specific proteins to be visualized by the interaction of antibodies with an enzyme-substrate-chromogen system. Here, we describe indirect immunohistochemistry method for paraffin-embedded mouse ovaries fixed with Bouin's Fixative.

Fibrinogen Demonstration in Oral Lichen Planus: An Immunofluorescence Study on Archival Tissues

BACKGROUND

Lichen planus is a premalignant condition with minimal diagnostic aids. This study is an attempt to use paraffin embedded sections of lichen planus with immunofluorescein stain and to evaluate the immunofluorescent sections to establish pattern of fibrinogen deposition.

MATERIALS AND METHODS

Thirty-five paraffin embedded sections of old and new cases of oral lichen planus (study group) and five normal oral mucosa (control group) were chosen. Two sections of each (H & E) case were taken, one was stained with hematoxylin and eosin and another with fluorescein isothiocynate conjugate (FITC) polyclonal rabbit antibody against fibrinogen. Fluorescent findings were examined with a fluorescent microscope.

RESULTS

A high statistical significant correlation was found in respect to fluorescence positivity, intensity of fluorescence and distribution of fluorescence each with p < 0.0001 and fluorescence at blood vessel walls (p = 0.0003).

CONCLUSION

This study suggested that paraffin embedded sections can be successfully used in direct immunofluorescence staining in routine set up where only formalin fixed tissues are received.

CLINICAL SIGNIFICANCE

Paraffin embedded sections can be successfully used in direct immunofluorescence staining when only formalin fixed tissues are received.