Multiple antigen immunostaining procedures

A method for quantitative spatial analysis of immunolabeled fibers at regenerative electrode interfaces

BACKGROUND

Regenerative electrodes are being explored as robust peripheral nerve interfaces for neuro-prosthetic control and sensory feedback. Current designs differ in electrode number, spatial arrangement, and porosity which impacts the regeneration, activation, and spatial distribution of fibers at the device interface. Knowledge of sensory and motor fiber distributions are important in optimizing selective fiber activation and recording.

NEW METHOD

We use confocal microscopy and immunofluorescence methods to conduct spatial analysis of immunolabeled fibers across whole nerve cross sections.

RESULTS

This protocol was implemented to characterize motor fiber distribution within 3 macro-sieve electrode regenerated (MSE), 3 silicone-conduit regenerated, and 3 unmanipulated control rodent sciatic nerves. Total motor fiber counts were 1485 [SD: +/- 50.11], 1899 [SD: +/- 359], and 5732 [SD: +/- 1410] for control, MSE, and conduit nerves respectively. MSE motor fiber distributions exhibited evidence of deviation from complete spatial randomness and evidence of dispersion and clustering tendencies at varying scales. Notably, MSE motor fibers exhibited clustering within the central portion of the cross section, whereas conduit regenerated motor fibers exhibited clustering along the periphery.

COMPARISON WITH EXISTING METHODS

Prior exploration of fiber distributions at regenerative interfaces was limited to either quadrant-based density analysis of randomly sampled subregions or qualitative description. This method extends existing sample preparation and microscopy techniques to quantitatively assess immunolabeled fiber distributions within whole nerve cross-sections.

CONCLUSIONS

This approach is an effective way to examine the spatial organization of fiber subsets at regenerative electrode interfaces, enabling robust assessment of fiber distributions relative to electrode arrangement.

Engineered Protein-G variants for plug-and-play applications

We have developed a portfolio of antibody-based modules that can be prefabricated as standalone units and snapped together in plug-and-play fashion to create uniquely powerful multifunctional assemblies. The basic building blocks are derived from multiple pairs of native and modified Fab scaffolds and protein G (PG) variants engineered by phage display to introduce high pair-wise specificity. The variety of possible Fab-PG pairings provides a highly orthogonal system that can be exploited to perform challenging cell biology operations in a straightforward manner. The simplest manifestation allows multiplexed antigen detection using PG variants fused to fluorescently labeled SNAP-tags. Moreover, Fabs can be readily attached to a PG-Fc dimer module which acts as the core unit to produce plug-and-play IgG-like assemblies, and the utility can be further expanded to produce bispecific analogs using the "knobs into holes" strategy. These core PG-Fc dimer modules can be made and stored in bulk to produce off-the-shelf customized IgG entities in minutes, not days or weeks by just adding a Fab with the desired antigen specificity. In another application, the bispecific modalities form the building block for fabricating potent Bispecific T-cell Engagers (BiTEs), demonstrating their efficacy in cancer cell-killing assays. Additionally, the system can be adapted to include commercial antibodies as building blocks, greatly increasing the target space. Crystal structure analysis reveals that a few strategically positioned interactions engender the specificity between the Fab-PG variant pairs, requiring minimal changes to match the scaffolds for different possible combinations. This plug-and-play platform offers a user-friendly and versatile approach to enhance the functionality of antibody-based reagents in cell biology research.

Immunolabelling perturbs the endogenous and antibody-conjugated elemental concentrations during immuno-mass spectrometry imaging

Immuno-mass spectrometry imaging uses lanthanide-conjugated antibodies to spatially quantify biomolecules via laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The multi-element capabilities allow for highly multiplexed analyses that may include both conjugated antibodies and endogenous metals to reveal relationships between disease and chemical composition. Sample handling is known to perturb the composition of the endogenous elements, but there has been little investigation into the effects of immunolabelling and coverslipping. Here, we used cryofixed muscle sections to examine the impact of immunolabelling steps on the concentrations of a Gd-conjugated anti-dystrophin primary antibody, and the endogenous metals Cu and Zn. Primary antibody incubation resulted in a decrease in Zn, and an increase in Cu. Zn was removed from the cytoplasm where it was hypothesised to be more labile, whereas concentrated locations of Zn remained in the cell membrane in all samples that underwent the immunostaining process. Cu increased in concentration and was found mostly in the cell membrane. The concentration of the Gd-conjugated antibody when compared to the standard air-dried sample was not significantly different when coverslipped using an organic mounting medium, whereas use of an aqueous mounting medium significantly reduced the concentration of Gd. These results build on the knowledge of how certain sample handling techniques change elemental concentrations and distributions in tissue sections. Immunolabelling steps impact the concentration of endogenous elements, and separate histological sections are required for the quantitative analysis of endogenous elements and biomolecules. Additionally, coverslipping tissue sections for complementary immunohistochemical/immunofluorescent imaging may compromise the integrity of the elemental label, and organic mounting media are recommended over aqueous mounting media.

Assessment of Connective Tissue in the Equine Uterus and Cervix: Review of Clinical Impact and Staining Options

Uterine diseases stand as the primary cause of infertility in mares; however, the diagnostic process often relies on obtaining endometrial biopsies and their hematoxylin-eosin staining. This review seeks to present the variability of uterine changes and their impact on fertility and underscore the utility of special stains, such as Masson trichrome, picrosirius red, elastica van Gieson, or periodic acid-Schiff, in enhancing diagnostic breadth. Connective tissue evaluation in the cervix is discussed, as it is subjected to cyclic changes and the impact on overall fertility. Vascular changes, particularly prevalent in multiparous mares, play a crucial role in adapting to physiological and pathological alterations, affecting early gestation and impeding placental development. Given that uterine vascular pathologies often involve fibrotic changes, connective tissue stains emerge as a valuable tool in this context. Moreover, equine endometriosis, predominantly associated with endometrial fibrosis, further highlights the relevance of special stains, suggesting their underutilization in the diagnostic process. Recognizing the subjective nature of diagnosing uterine pathologies and the need for additional diagnostic tools, we advocate for using dedicated stains in the histopathological evaluation of uterine samples. In conclusion, we encourage scientists and diagnosticians to embrace additional tools that enhance pathology visualization, enabling more reliable diagnoses concerning expected fertility.

TUNEL-n-DIFL Method for Detection and Estimation of Apoptosis Specifically in Neurons and Glial Cells in Mixed Culture and Animal Models of Central Nervous System Diseases and Injuries

Detection of merely apoptosis does not reveal the type of central nervous system (CNS) cells that are dying in the CNS diseases and injuries. In situ detection and estimation of amount of apoptosis specifically in neurons or glial cells (astrocytes, oligodendrocytes, and microglia) can unveil valuable information for designing therapeutics for protection of the CNS cells and functional recovery. A method was first developed and reported from our laboratory for in situ detection and estimation of amount of apoptosis precisely in neurons and glial cells using in vitro and in vivo models of CNS diseases and injuries. This is a combination of terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and double immunofluorescent labeling (DIFL) or simply TUNEL-n-DIFL method for in situ detection and estimation of amount of apoptosis in a specific CNS cell type. An anti-digoxigenin (DIG) IgG antibody conjugated with 7-amino-4-methylcoumarin-3-acetic acid (AMCA) for blue fluorescence, fluorescein isothiocyanate (FITC) for green fluorescence, or Texas Red (TR) for red fluorescence can be used for in situ detection of apoptotic cell DNA, which is earlier labeled with TUNEL using alkali-stable DIG-11-dUTP. A primary anti-NeuN (neurons), anti-GFAP (astrocytes), anti-MBP (oligodendrocytes), or anti-OX-42 (microglia) IgG antibody and a secondary IgG antibody conjugated with one of the above fluorophores (other than that of ani-DIG antibody) are used for in situ detection of apoptosis in a specific CNS cell type in the mixed culture and animal models of the CNS diseases and injuries.

Immunohistochemical Detection of SARS-CoV-2 Antigens by Single and Multiple Immunohistochemistry

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection can be demonstrated in tissue sections by immunohistochemistry (IHC), which has the power to localize in bright field specific antigens in cells and tissues. The use of double or triple immunostains is capable of highlighting which cells are infected and/or the relationship of infected cell with other cells and tissue structures. In addition, immunoenzymatic multi-staining permits the simultaneous identification, localization, and enumeration of different cellular epitopes. Moreover, this method improves analytical precision, decreasing the time required for morphometric quantification, maximizing the information obtained from a single slide of paraffin-embedded tissue.

A manual multiplex immunofluorescence method for investigating neurodegenerative diseases

BACKGROUND

Neurodegenerative diseases feature stereotypical deposits of protein aggregates that selectively accumulate in vulnerable cells. The ability to simultaneously localize multiple targets in situ is critical to facilitate discovery and validation of pathogenic molecular pathways. Immunostaining methods enable in situ detection of specific targets. Effective stripping of antibodies, allowing successive rounds of staining while maintaining tissue adhesion and antigen integrity, is the main roadblock for enabling multiplex immunostaining in standard labs. Furthermore, stripping techniques require antibody-specific optimization, validation, and quality control steps.

NEW METHOD

Aiming to create protocols for multiplex localization of neurodegenerative-related processes, without the need for specialized equipment, we evaluated several antibody stripping techniques. We also recommend quality control steps to validate stripping efficacy and ameliorate concerns of cross-reactivity and false positives based on extensive testing.

RESULTS

A protocol using β-mercaptoethanol and SDS consistently enables reliable antibody stripping across multiple rounds of staining and minimizes the odds of cross-reactivity while preserving tissue adhesion and antigen integrity in human postmortem tissue.

COMPARISON WITH EXISTING METHODS

Our proposed method is optimal for standard lab settings and shows consistent efficacy despite the intricacies of suboptimal human postmortem tissue and the need to strip markers bound to highly aggregated proteins. Additionally, it incorporates quality control steps to validate antibody stripping.

CONCLUSIONS

Multiplex immunofluorescence methods for studying neurodegenerative diseases in human postmortem tissue are feasible even in standard laboratories. Nevertheless, evaluation of stripping parameters during optimization and validation phases of experiments is prudent.

High-throughput analysis of tissue-based biomarkers in digital pathology

By simultaneously processing a large number of tissue samples, the tissue microarray (TMA) technology allows standardized screening of protein expression using immunohistochemistry thereby providing a very efficient way for tissue-based biomarker analysis. Nowadays, whole slide imaging is becoming standard in digital pathology and enables image sharing, archiving and also processing. In this paper, we present methods for processing TMA images in order to correctly identify the numerous tissue samples and to register images from consecutive TMA sections.

Registration of whole immunohistochemical slide images: an efficient way to characterize biomarker colocalization

BACKGROUND AND OBJECTIVE

Extracting accurate information from complex biological processes involved in diseases, such as cancers, requires the simultaneous targeting of multiple proteins and locating their respective expression in tissue samples. This information can be collected by imaging and registering adjacent sections from the same tissue sample and stained by immunohistochemistry (IHC). Registration accuracy should be on the scale of a few cells to enable protein colocalization to be assessed.

METHODS

We propose a simple and efficient method based on the open-source elastix framework to register virtual slides of adjacent sections from the same tissue sample. We characterize registration accuracies for different types of tissue and IHC staining.

RESULTS

Our results indicate that this technique is suitable for the evaluation of the colocalization of biomarkers on the scale of a few cells. We also show that using this technique in conjunction with a sequential IHC labeling and erasing technique offers improved registration accuracies.

DISCUSSION

Brightfield IHC enables to address the problem of large series of tissue samples, which are usually required in clinical research. However, this approach, which is simple at the tissue processing level, requires challenging image analysis processes, such as accurate registration, to view and extract the protein colocalization information.

CONCLUSIONS

The method proposed in this work enables accurate registration (on the scale of a few cells) of virtual slides of adjacent tissue sections on which the expression of different proteins is evidenced by standard IHC. Furthermore, combining our method with a sequential labeling and erasing technique enables cell-scale colocalization.

4FISH-IF, a four-color dual-gene FISH combined with p63 immunofluorescence to evaluate NKX3.1 and MYC status in prostate cancer

NKX3.1 allelic loss and MYC amplification are common events during prostate cancer progression and have been recognized as potential prognostic factors in prostate cancer after radical prostatectomy or precision radiotherapy. We have developed a 4FISH-IF assay (a dual-gene fluorescence in situ hybridization combined with immunofluorescence) to measure both NKX3.1 and MYC status on the same slide. The 4FISH-IF assay contains four probes complementary to chromosome 8 centromere, 8p telomere, 8p21, and 8q24, as well as an antibody targeting the basal cell marker p63 visualized by immunofluorescence. The major advantages of the 4FISH-IF include the distinction between benign and malignant glands directly on the 4FISH-IF slide and the control of truncation artifact. Importantly, this specialized and innovative combined multiprobe and immunofluorescence technique can be performed on diagnostic biopsy specimens, increasing its clinical relevance. Moreover, the assay can be easily performed in a standard clinical molecular pathology laboratory. Globally, the use of 4FISH-IF decreases analytic time, increases confidence in obtained results, and maintains the tissue morphology of the diagnostic specimen.

Collagen XVII is expressed in malignant but not in benign melanocytic tumors and it can mediate antibody induced melanoma apoptosis

The 180 kDa transmembrane collagen XVII is known to anchor undifferentiated keratinocytes to the basement membrane in hemidesmosomes while constitutively shedding a 120 kDa ectodomain. Inherited mutations or auto-antibodies targeting collagen XVII cause blistering skin disease. Collagen XVII is down-regulated in mature keratinocytes but re-expressed in skin cancer. By recently detecting collagen XVII in melanocyte hyperplasia, here we tested its expression in benign and malignant melanocytic tumors using endodomain and ectodomain selective antibodies. We found the full-length collagen XVII protein in proliferating tissue melanocytes, basal keratinocytes and squamous cell carcinoma whereas resting melanocytes were negative. Furthermore, the cell-residual 60 kDa endodomain was exclusively detected in 62/79 primary and 15/18 metastatic melanomas, 8/9 melanoma cell lines, HT199 metastatic melanoma xenografts and atypical nests in 8/63 dysplastic nevi. The rest of 19 nevi including common, blue and Spitz subtypes were also negative. In line with the defective ectodomain, sequencing of COL17A1 gene revealed aberrations in the ectodomain coding region including point mutations. Collagen XVII immunoreaction-stained spindle cell melanomas, showed partly overlapping profiles with those of S100B, Melan A and HMB45. It was concentrated at vertical melanoma fronts and statistically associated with invasive phenotype. Antibody targeting the extracellular aa507-529 terminus of collagen XVII endodomain promoted apoptosis and cell adhesion, while inhibiting proliferation in HT199 cells. These results suggest that the accumulation of collagen XVII endodomain in melanocytic tumors is associated with malignant transformation to be a potential marker of malignancy and a target for antibody-induced melanoma apoptosis.

Epidermal growth factor receptor signalling contributes to osteoblastic stromal cell proliferation, osteoclastogenesis and disease progression in giant cell tumour of bone

AIMS

Epidermal growth factor receptor (EGFR) is implicated in bone remodelling. The aim was to determine whether EGFR protein expression contributes to the aggressiveness and recurrence potential of giant cell tumour of bone (GCTB), an osteolytic primary bone tumour that can exhibit markedly variable clinical behaviour.

METHODS AND RESULTS

Immunohistochemical analysis on tissue microarrays (TMA) of 231 primary, 97 recurrent, 17 metastatic and 26 malignant GCTBs was performed using TMA analysis software and whole digital slides allowing validated scoring. EGFR expression was restricted to neoplastic stromal cells and was significantly more frequent in recurrent (71 of 92; 77%) than in non-recurrent GCTBs (86 of 162; 53%) (P = 0.002); and in clinicoradiologically aggressive (31 of 43; 72%) than latent (27 of 54; 50%) cases (P = 0.034). Detecting phosphotyrosine epitopes pY1068 and -pY1173 indicated active EGFR signalling, and finding EGFR ligands EGF and transforming growth factor-α restricted to cells of the monocytic lineage suggested paracrine EGFR activation in stromal cells. In functional studies EGF supported proliferation of GCTB stromal cells, and the addition of EGF and macrophage-colony stimulating factor promoted osteoclastogenesis.

CONCLUSION

In GCTB, EGFR signalling in neoplastic stromal cells may contribute to disease progression through promoting stromal cell proliferation and osteoclastogenesis.