Detection of Changes in Immunohistochemical Stains Caused by Postmortem Delay and Fixation Time

Differential effects of prolonged post-fixation on immunohistochemical and histochemical staining for postmortem human brains

Purpose

Immunohistochemical (IHC) and histochemical (HC) staining techniques are widely used on human brains that are post-fixed in formalin and stored in brain banks worldwide for varying durations, from months to decades. Understanding the effects of prolonged post-fixation, postmortem interval (PMI), and age on these staining procedures is important for accurately interpreting their outcomes, thereby improving the diagnosis and research of brain disorders afflicting millions of people worldwide.

Methods

In this study, we conducted both IHC and HC staining on the prefrontal cortex of postmortem human brains post-fixed for 1, 5, 10, 15, and 20 years. For IHC staining, we used two antibodies for each marker: the neuron marker neuronal nuclear antigen (NeuN), the astrocyte marker glial fibrillary acidic protein (GFAP), and the microglia marker ionized calcium-binding adaptor molecule 1 (Iba1). For HC staining, we conducted hematoxylin and eosin Y (H&E), cresyl violet (CV), and Luxol fast blue (LFB) stains to examine neuropils, neurons, and myelin, respectively.

Results

We observed that the intensity of NeuN, Iba1, CV, or LFB staining was negatively correlated with post-fixation durations. Conversely, we detected a positive correlation between the intensity of GFAP and H&E staining and post-fixation durations. Moreover, there was no correlation between the intensity of NeuN, GFAP, Iba1, H&E, CV, and LFB staining and PMI. Additionally, no correlation was found between these staining intensities and age, except for the intensity of GFAP immunostained by one antiserum, which was negatively correlated with age.

Conclusion

Taken together, these findings suggest that prolonged post-fixation has both positive and negative effects, while age and PMI exert limited influence on these IHC and HC parameters. Therefore, it is essential to consider these differential changes when interpreting results derived from tissues with extended post-fixation durations. Furthermore, if feasible, we recommend conducting IHC and HC staining on human brains with the same post-fixation time spans and using the most optimal antibodies to mitigate the impact on subsequent analyses.

Double Chromogen-based Immunohistochemical Staining: An Efficient Approach for Utilizing Long-term Formalin-fixed Tissue in Biobanks

The New South Wales Brain Tissue Resource Centre is a human brain bank that provides top-quality brain tissue for cutting-edge neuroscience research spanning various conditions from alcohol use disorder to neurodegenerative diseases. However, the conventional practice of preserving brain tissue in formalin poses challenges for immunofluorescent staining primarily due to the formalin's tendency, over time, to create cross-links between antigens, which can obscure epitopes of interest. In addition, researchers can encounter issues such as spectral bleeding, limitations in using multiple colors, autofluorescence, and cross-reactivity when working with long-term formalin-fixed brain tissue. The purpose of the study was to test chromogen-based double immunolabeling to negate the issues with immunofluorescent staining. Colocalization of antigens was explored using chromogens 3-amino-9-ethylcarbazole (AEC) and 3,3,-diaminobenzidine in a sequential staining procedure where the AEC signal was eliminated by alcohol treatment. Combinations of 2 or 3 primary antibodies from the same or different species were trialed successfully with this protocol. The colocalization of antigens was also demonstrated with pseudocoloring that mimicked immunofluorescence staining. This staining technique increases the utility of archival formalin-fixed tissue samples.

Higher densities of T-lymphocytes in the subsynovial connective tissue of people with carpal tunnel syndrome

Symptoms in people with carpal tunnel syndrome (CTS) are traditionally attributed to neural tissue, but recent studies suggest that the subsynovial connective tissue (SSCT) may also play a role in CTS. The SSCT undergoes fibrotic thickening which is generally described as "non-inflammatory" based on basic histology. This study uses immunohistochemistry to determine the presence of macrophages and T-cells within SSCT and their relationship with symptoms in people with CTS. SSCT was collected from twenty people with CTS and eight controls undergoing wrist fracture surgery. Immunohistochemical quantification of CD3+ T-cells and CD68+ macrophage densities as well as CD4+/CD8+ T-cell subpopulations were compared between groups using independent t-tests. Spearman correlations were used to identify associations between immune cell densities and CTS symptom scores. The density of CD3+ T-cells was significantly higher in SSCT of people with CTS compared to controls (CTS mean 26.7 (SD 13.7); controls 6.78 (6.3), p = 0.0005) while the density of CD68+ macrophages was lower (CTS mean 9.5 (SD 6.0); controls 17.7 (8.2), p = 0.0058). Neither CD68+ nor CD3+ cell densities correlated with symptom scores. In contrast to previous assumptions, our data show that the SSCT in the carpal tunnel in both people with CTS and controls is not devoid of immune cells. Whereas the higher density of CD68+ macrophages in control participants may be associated with their early recruitment after acute fracture, CD3+ cells within the SSCT may play a role in chronic CTS.

Collagen type XII is undetectable in keratoconus Bowman's layer

PURPOSE

Corneal biomechanical failure is the hallmark of keratoconus (KC); however, the cause of this failure remains elusive. Collagen type XII (COL12A1), which localises to Bowman's layer (BL), is thought to function in stress-bearing areas, such as BL. Given the putative protective role of COL12A1 in biomechanical stability, this study aims to characterise COL12A1 expression in all corneal layers involved in KC.

METHODS

TaqMan quantitative PCR was performed on 31 corneal epithelium samples of progressive KC and myopic control eyes. Tissue microarrays were constructed using full-thickness corneas from 61 KC cases during keratoplasty and 18 non-KC autopsy eyes and stained with an antibody specific to COL12A1. Additionally, COL12A1 was knocked out in vitro in immortalised HEK293 cells.

RESULTS

COL12A1 expression was reduced at transcript levels in KC epithelium compared with controls (ratio: 0.58, p<0.03). Immunohistochemical studies demonstrated that COL12A1 protein expression in BL was undetectable, with reduced expression in KC epithelium, basement membrane and stroma.

CONCLUSIONS

The apparent absence of COL12A1 in KC BL, together with the functional importance that COL12A1 is thought to have in stress bearing areas, suggests that COL12A1 may play a role in the pathogenesis of KC. Further studies are necessary to investigate the mechanisms that lead to COL12A1 dysregulation in KC.

Interspecies Retinal Diversity and Optic Nerve Anatomy in Odontocetes

Throughout evolution, odontocete vision has had to readapt to the aquatic environment, which has had far-reaching effects on ocular anatomy and neurology. The most prominent features include the iris with an operculum, a well-developed choroid, the presence of giant ganglion cells in the retina, and the hemispherical shape of the thick eyecup. In the present study, the optic nerve and the retina were comparatively studied in Odontoceti (Cuvier's beaked whale, common bottlenose dolphin, false killer whale, long-finned pilot whale, Risso's dolphin, striped dolphin), the semi-aquatic common hippopotamus, and the fully terrestrial bovine. Cross-sections of the tissue were treated with histological and immunohistochemical techniques. Substantial differences were seen between the odontocetes and the reference species as well as within the cetaceans. The morphological structure of the optic nerve mainly appeared species specific, while the density of retinal ganglion cells was significantly higher in the terrestrial bovine than in the cetaceans. However, some typical characteristics of the cetacean retina were absent: the giant ganglion cells and the high retinal thickness. Immunohistochemical research showed varying degrees of neurofilament 200 expression in the retinal ganglion cells, while calretinin was only expressed in those of the common bottlenose dolphin and bovine.

The impact of impaired tissue fixation in resected non-small-cell lung cancer on protein deterioration and DNA degradation

OBJECTIVES

The objective is to assess the impact of the quality of tissue fixation in surgical pathology on immunohistochemical (IHC) staining and DNA degradation.

MATERIALS AND METHODS

Twenty-five non-small cell lung cancer (NSCLC) resection specimens were analyzed. After resection, all tumors were processed according to the protocols in our center. In haematoxylin and eosin (H&E) stained tissue slides, adequately- and inadequately fixed tumor areas were microscopically demarcated, based on basement membrane detachment. In 10 IHC stains ALK (clone 5A4), PD-L (clone 22C3), CAM5.2, CK7, c-Met, KER-MNF116, NapsinA, p40, ROS1, TTF1) the immunoreactivity in H-scores was determined in adequately- and inadequately fixed, and necrotic tumor areas. From the same areas DNA was isolated, and DNA fragmentation in base pairs (bp) was measured.

RESULTS

H-scores were significantly higher in H&E adequately fixed tumor areas in IHC stains KER-MNF116 (H-score 256 vs 15, p=0.001) and p40 (H-score 293 vs 248, p=0.028). All other stains showed a trend towards higher immunoreactivity in H&E adequately fixed areas. Independent of H&E adequatelty- or inadequately fixed areas, all IHC stains showed significant different IHC staining intensity within tumors, suggesting heterogeneous immunoreactivity (H-scores: PD-L1 123 vs 6, p = 0.001; CAM5.2 242 vs 101, p=<0.001; CK7 242 vs 128, p=<0.001; c-MET 99 vs 20, p=<0.001; KER-MNF116 281 vs 120, p=<0.001; Napsin A 268 vs 130, p = 0.005; p40 292 vs 166, p = 0.008; TTF1 199 vs 63, p=<0.001). DNA fragments rarely exceeded a length of 300 bp, independent of adequate fixation. However, DNA fragments of 300 and 400 bp had higher concentrations in tumors with short fixation delay (<6 h vs >16 h) and short fixation time (<24 h vs >24 h).

CONCLUSIONS

Impaired tissue fixation of resected lung tumors results in decreased IHC staining intensity in some parts of the tumor. This may impact the reliability of IHC analysis.

The effect of prolonged formalin fixation on the expression of proteins in human brain tissues

Formalin-fixed, paraffin-embedded (FFPE) tissues have been widely used in researches. Proteins and nucleic acids in prolonged FFPE tissues display different degrees of degradation. We investigated the effect of prolonged formalin fixation on protein expression in human brain tissues. Twenty-eight middle prefrontal front cortex tissue blocks from human brains prefixed in formalin were obtained from a brain bank. The tissue blocks were divided into two groups, the control group and the prolonged fixation group. Quantitative immunocytochemistry was used to analyse the biological markers of Fox-3, Rbfox3 (NeuN), glial fibrillary acidic protein (GFAP), ionized calcium binding adapter molecule-1 (IBA-1) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Nissl staining showed that positive signaling of Nissl body was significantly decreased by 16.6% in the prolonged fixation group. In addition, the staining intensity of Nissl body was negatively correlated with fixation time. The level of NeuN immunoreactivity (ir) was significantly reduced by 19.31% in the prolonged fixation group. Moreover, there was a significant negative correlation between NeuN-ir and fixation time. There were no significant changes in GFAP-ir, IBA-1-ir and GAPDH-ir between control group and the prolonged fixation group. Prolonged formalin-fixed tissues showed time- and molecule-dependent protein changes, which may be potential confounders in the clinic and researches. Our study suggested short formalin fixation time is recommended when using PPFE brain tissues.

Mixed Pathologies in a Subject with a Novel PSEN1 G206R Mutation

BACKGROUND

There are more than 300 presenilin-1 (PSEN1) mutations identified but a thorough postmortem neuropathological assessment of the mutation carriers is seldom performed.

OBJECTIVE

To assess neuropathological changes (NC) in a 73-year-old subject with the novel PSEN1 G206R mutation suffering from cognitive decline in over 20 years. To compare these findings with an age- and gender-matched subject with sporadic Alzheimer's disease (sAD).

METHODS

The brains were assessed macro- and microscopically and the proteinopathies were staged according to current recommendations.

RESULTS

The AD neuropathological change (ADNC) was more extensive in the mutation carrier, although both individuals reached a high level of ADNC. The transactive DNA binding protein 43 pathology was at the end-stage in the index subject, a finding not previously described in familial AD. This pathology was moderate in the sAD subject. The PSEN1 G206R subject displayed full-blown alpha-synuclein pathology, while this proteinopathy was absent in the sAD case. Additionally, the mutation carrier displayed pronounced neuroinflammation, not previously described in association with PSEN1 mutations.

CONCLUSION

Our findings are exceptional, as the PSEN1 G206R subject displayed an end-stage pathology of every common proteinopathy. It is unclear whether the observed alterations are caused by the mutation or are related to a cross-seeding mechanisms. The pronounced neuroinflammation in the index patient can be reactive to the extensive NC or a contributing factor to the proteinopathies. Thorough postmortem neuropathological and genetic assessment of subjects with familial AD is warranted, for further understanding of a dementing illness.

Immunostaining for NeuN Does Not Show all Mature and Healthy Neurons in the Human and Pig Brain: Focus on the Hippocampus

Neuronal nuclei (NeuN) is a neuron-specific nuclear protein, reported to be stably expressed in most postmitotic neurons of the vertebrate nervous system. Reduced staining has been interpreted by some to indicate loss of cell viability in human studies, while others suggest this may be because of changes in the antigenicity of the target epitope. Preliminary studies in our laboratory found low immunostaining for the NeuN antibody on formalin fixed and paraffin embedded (FFPE) human brain tissue. We report on the techniques and results used to enhance the staining for NeuN in that tissue. In parallel, we stained NeuN in piglet brain tissue, sourced from an experimental model where methodological parameters, including those for tissue fixation and storage, were tightly controlled. In human FFPE brain tissue, we were unable to enhance NeuN immunostaining to a degree sufficient for cell counting. In contrast, we found consistently high levels of staining in the piglet brain tissue. We conclude that processes used for fixation and storage of human FFPE brain tissue are responsible for the reduced staining. These results emphasize that a cautionary approach should be taken when interpreting NeuN staining outcomes in human FFPE brain tissue.

Differential DNA Methylation of the Genes for Amyloid Precursor Protein, Tau, and Neurofilaments in Human Traumatic Brain Injury

Traumatic brain injury (TBI) is an established risk factor for neurodegenerative disorders and dementias. Epigenetic modifications, such as DNA methylation, may alter the expression of genes without altering the DNA sequence in response to environmental factors. We hypothesized that DNA methylation changes may occur in the injured human brain and be implicated in the neurodegenerative aftermath of TBI. The DNA methylation status of genes related to neurodegeneration; for example, amyloid beta precursor protein (APP), microtubule associated protein tau (MAPT), neurofilament heavy (NEFH), neurofilament medium (NEFM), and neurofilament light (NEFL), was analyzed in fresh, surgically resected human brain tissue from 17 severe TBI patients and compared with brain biopsy samples from 19 patients with idiopathic normal pressure hydrocephalus (iNPH). We also performed an epigenome-wide association study (EWAS) comparing TBI patients with iNPH controls. Thirty-eight CpG sites in the APP, MAPT, NEFH, and NEFL genes were differentially methylated by TBI. Among the top 20 differentially methylated CpG sites, 11 were in the APP gene. In addition, the EWAS evaluating 828,888 CpG sites revealed 308 differentially methylated CpG sites in genes related to cellular/anatomical structure development, cell differentiation, and anatomical morphogenesis. These preliminary findings provide the first evidence of an altered DNA methylome in the injured human brain, and may have implications for the neurodegenerative disorders associated with TBI.

Nonclassified Lymphoma as a Cause of Radial Nerve Paralysis in a Horse

A 4-year-old American Quarter Horse gelding was evaluated for acute non-weight-bearing lameness of the right thoracic limb with swelling in the right shoulder region. Physical examination revealed radial nerve paralysis of unknown etiology. The primary differential diagnosis was musculoskeletal trauma. Ultrasonography of the right shoulder region identified a heterogeneous mass that extended from the point of the shoulder to the thoracic inlet. Cytologic analysis of fluid collected by fine needle aspirate of the mass was consistent with large cell lymphoma. Based on the cytological findings, locally invasive neoplasia was diagnosed and considered the likely cause of the radial nerve paralysis. Because of the poor prognosis, the horse was euthanized, and postmortem examination confirmed the diagnosis of a nonclassified large cell lymphoma that extended from the deep tissues of the right pectoral muscle group into the thoracic inlet and pleural cavity, as well as the right brachial plexus. The mass in the region of the brachial plexus encompassed and mechanically compressed all of the nerves within the area, resulting in the clinical sign of radial nerve paralysis. Although neoplasia as a cause of radial nerve paralysis is rare, it should be considered as a differential diagnosis, regardless of age.

RbAp48 expression and neuronal damage in the gerbil hippocampus following 5 min of transient ischemia

Histone-binding protein RbAp48 has been known to be involved in histone acetylation, and epigenetic alterations of histone modifications are closely associated with the pathogenesis of ischemic reperfusion injury. In the current study, we investigated chronological change of RbAp48 expression in the hippocampus following 5 min of transient ischemia in gerbils. RbAp48 expression was examined 1, 2, 5, and 10 days after transient ischemia using immunohistochemistry. In sham operated gerbils, RbAp48 immunoreactivity was strong in pyramidal and non-pyramidal cells in the hippocampus. After transient ischemia, RbAp48 immunoreactivity was changed in the cornu ammonis 1 subfield (CA1), not in CA2/3. RbAp48 immunoreactivity in CA1 pyramidal neurons was gradually decreased and not detected at 5 and 10 days after ischemia. RbAp48 immunoreactivity in non-pyramidal cells was maintained until 2 days post-ischemia and significantly increased from 5 days post-ischemia. Double immunohistofluorescence staining revealed that RbAp48 immunoreactive non-pyramidal cells were astrocytes. At 5 days post-ischemia, death of pyramidal neurons occurred only in the CA1. These results showed that RbAp48 immunoreactivity was distinctively altered in pyramidal neurons and astrocytes in the hippocampal CA1 following 5 mins of transient ischemia. Ischemia-induced change in RbAp48 expression may be closely associated with neuronal death and astrocyte activation following 5 min of transient ischemia.

Impact of delayed and prolonged fixation on the evaluation of immunohistochemical staining on lung carcinoma resection specimen

Pre-analytical factors, such as fixation time, influence morphology of diagnostic and predictive immunohistochemical staining, which are increasingly used in the evaluation of lung cancer. Our aim was to investigate if variations in fixation time influence the outcome of immunohistochemical staining in lung cancer. From lung resections, specimen with tumor size bigger than 4 cm, 10 samples were obtained: 2 were put through the standard fixation protocol, 5 through the delayed, and 3 through the prolonged fixation protocol. After paraffin embedding, tissue microarrays (TMAs) were made. They were stained with 20 antibodies and scored for quality and intensity of staining. Samples with delay in fixation showed loss of TMA cores on glass slides and deterioration of tissue quality leading to reduction in the expression of CK 7, Keratin MNF116, CAM 5.2, CK 5/6, TTF-1, C-MET, Napsin A, D2-40, and PD-L1. Prolonged fixation had no influence on the performance of immunohistochemical stains. Delay of fixation negatively affects the expression of different immunohistochemical markers, influencing diagnostic (cytokeratins) and predictive (PD-L1) testing. These results emphasize the need for adequate fixation of resection specimen.

Imaging of post-mortem human brain tissue using electron and X-ray microscopy

Electron microscopy imaging of post-mortem human brain (PMHB) comes with a unique set of challenges due to numerous parameters beyond the researcher's control. Nevertheless, the wealth of information provided by the ultrastructural analysis of PMHB is proving crucial in our understanding of neurodegenerative diseases. This review highlights the importance of such studies and covers challenges, limitations and recent developments in the application of current EM imaging, including cryo-ET and correlative hybrid techniques, on PMHB.

Characteristics of the tissue section that influence the staining outcome in immunohistochemistry

Immunohistochemistry (IHC) is influenced by several factors such as cold ischemia time, fixative, fixation time, paraffin, storage time, antibody, antigen retrieval technique and detection systems. In the setting of post-mortem tissue, not only post-mortem delay, but also agonal state is of interest. Here, we assessed an additional variable, i.e., the thickness of the section, and noted that this variable also influenced the IHC outcome. This is of significance when the extent of labelling is a parameter to be assessed, for example when assigning a stage or grade of a disease. Furthermore, when assessing brain tissue with neurons, soma measuring from 4 to 100 µm, various cellular compartments composed of different proteins are localised in sections measuring 4 or 7 µm. Thus, what is seen in a 7-µm-thick section might be lacking in a 4-µm-thick section. Lack of information regarding the molecular size of commercial antibodies is also disturbing as this parameter might influence the distribution of the molecule in the three-dimensional section. The choice of antibody to be used and the staining methodology have been acknowledged being of significance for IHC outcome; however, neither sections thickness or the molecular weight has been discussed sufficiently. IHC has been shown to be an unpredictable technique used for assessment of tissue. This emphasises the need for detailed methodological descriptions in publications, the need to acknowledge and to harmonize all eventual pitfalls related to this methodology.

From fix to fit into the autoptic human brains

Formalin-fixed, paraffinembedded (FFPE) human brain tissues are very often stored in formalin for long time. Formalin fixation reduces immunostaining, and the DNA/RNA extraction from FFPE brain tissue becomes suboptimal. At present, there are different protocols of fixation and several procedures and kits to extract DNA/RNA from paraffin embedding tissue, but a gold standard protocol remains distant. In this study, we analyzed four types of fixation systems and compared histo and immuno-staining. Based on our results, we propose a modified method of combined fixation in formalin and formic acid for the autoptic adult brain to obtain easy, fast, safe and efficient immunolabelling of long-stored FFPE tissue. In particular, we have achieved an improved preservation of cellular morphology and obtained success in postmortem immunostaining for NeuN. This nuclear antigen is an important marker for mapping neurons, for example, to evaluate the histopathology of temporal lobe epilepsy or to draw the topography of cardiorespiratory brainstem nuclei in sudden infant death syndrome (SIDS). However, NeuN staining is frequently faint or lost in postmortem human brain tissues. In addition, we attained Fluoro Jade C staining, a marker of neurodegeneration, and immunofluorescent staining for stem cell antigens in the postnatal human brain, utilizing custom fit fixation procedures.