Double-staining methods at the ultrastructural level applying colloidal gold conjugates

Immunoelectron microscopy in the age of molecular pathology

The introduction of molecular biology-based diagnostic procedures in pathology has created substantial expectations in regard to screening, characterization, monitoring, and detection of predisposition to a variety of diseases, most notably malignant neoplasms. It should be emphasized, however, that molecular studies are only one component of the diagnostic process and that more traditional methods are still required in the evaluation of tumors and management of patients. The data obtained from the molecular biology-based studies must be always interpreted in conjunction with the clinical history, immunomorphologic findings, and other pertinent ancillary data. Routine evaluation of tissues using traditional light microscopy remains the backbone of pathologic evaluation. The additive role of molecular diagnostics often depends on how accurate the initial evaluation has been. Ancillary techniques such as immunohistochemistry and electron microscopy remain essential in properly characterizing diseased tissues and in speciation of tumors. Ultrastructural immunolabeling capitalizes on combining these two techniques and providing exquisite immunomorphologic evaluation. The extra time and effort required are more than compensated by the degree of sophistication that can be achieved when this diagnostic technique is utilized and the added expense is rather reasonable. The value of molecular biology-based diagnostics is potentially questionable if the tissue samples are not initially accurately characterized. The question that molecular diagnostics may be trying to answer may be the wrong one or the answer obtained may be interpreted incorrectly if the context of the clinicopathologic situation has not been clearly defined using traditional diagnostic techniques.

How to examine the antigen-damaging effect of sodium ethoxide on deplasticized epoxy sections

The purpose of this investigation was to develop a method that could be used to estimate how damaging sodium ethoxide is to different antigens with respect to immunolabeling when epoxy sections are deplasticized. If we obtain weak labeling for an antigen on deplasticized epoxy sections, this might be caused by the damaging effect of the ethoxide solution. It is therefore interesting to develop a method to check if this really is the reason. Fibrin clots and tissues of human kidney and thyroid were embedded in LR White resin. Some thin sections from these specimen blocks were exposed to sodium ethoxide in the same way as epoxy sections are when being deplasticized. Other sections from the same blocks were not exposed to sodium ethoxide. Both categories of sections were immunogold-labeled with anti-fibrinogen, anti-thyroglobulin, anti-IgA, anti-IgG, or anti-IgM. The intensity of immunolabeling of sections treated with ethoxide was compared with the immunolabeling of corresponding sections that were not treated with ethoxide. No significant differences were found in immunolabeling for fibrinogen, IgA, IgG, and IgM. For thyroglobulin, the intensity was approximately 30% less in tissues that were exposed to sodium ethoxide. The practical significance of this method is that we easily can examine the degree to which a given antigen is affected by sodium ethoxide, which is the agent used for deplasticizing epoxy sections.

Differentiating small round cell sarcomas of the soft parts by an innovative immunogold labeling method: an ultrastructural study

A new immunoelectron microscopy procedure was developed by remaking the fixed-frozen tissue specimens into LR White resin blocks suitable for postembedding colloidal gold immunolabeling, and used to examine 16 cases of small round cell soft tissue sarcomas. In rhabdomyosarcoma, ultrastructural double-immunogold staining demonstrated a coexpression of muscle specific actin and desmin in the same tumor cell. In both Ewing's sarcoma and peripheral neuroepithelioma, the heterogeneous expression of MIC2 gene product (p30/32MIC2) in each tumor cell was demonstrated as well. In peripheral neuroepithelioma, the colloidal gold immunolabeling for neurofilament demonstrated the intermediate filaments surrounding microtubules. The procedure for ultrastructural colloidal gold immunolabeling using fixed-frozen tissue is thus considered to be useful not only for tumor diagnosis, but also for investigating various subcellular structures.

Improved technique for immunoelectron microscopy. How to prepare epoxy resin to obtain approximately the same immunogold labeling for epoxy sections as for acrylic sections without any etching

The purpose of this study was to improve the immunogold labeling of epoxy sections and to increase our knowledge of the mechanism for how antigens become immunolabeled on resin sections. Tissues from pancreas, thyroid and fibrin clots were embedded in an epoxy resin and LR-White. The epoxy mixture was composed and treated in different ways, especially with respect to altered amounts of accelerator (DMP-30). Immunogold labeling was performed with anti-glucagon, anti-thyroglobulin and anti-fibrinogen respectively. By increasing the amount of DMP-30 in the infiltration steps and/or embedding step, we observed a significant rise in the immunogold labeling. For the largest proteins the labeling was up to 8 times more intense than the labeling achieve with epoxy sections produced by 'normal' amount of accelerator in the embedding mixture and without accelerator in the infiltration mixture. For the smallest protein, glucagon, the differences were almost absent. The labeling of thyroglobulin and fibrinogen on the high accelerator epoxy sections was up to 70% of the labeling of LR-White sections, while conventional epoxy sections showed a labeling of 5-10% of that obtained with acrylic labeling. The cutting qualities of the high-accelerator blocks were similar to that of conventional epoxy embedding. The ultrastructure of the sections from the high-accelerator epoxy blocks were good, and the contrast was improved when tannic acid was used as enhancer. Our theory to explain the improved labeling is that the antigens are less tightly incorporated in the polymer network when the concentration of the accelerator is increased. The method outlined significantly improves the detectability of antigens on epoxy sections, which is the embedding resin routinely used in many laboratories.

The theoretical relationship of immunogold labeling on acrylic sections and epoxy sections

The purpose of this study was to predict the ratio of immunogold labeling of LR-White sections and epoxy sections using theoretical methods. Tissues used in the experiments were pancreas, pituitary, kidney, thyroid and fibrin. Antigens used as test proteins were glucagon, somatostatin, thyroglobulin, chromogranin A, ACTH (adrenocorticotropt hormone), amyloid A and fibrinogen. These are proteins of different sizes. The quotient labelingLR-White/labelingepoxy was deduced theoretically and compared to calculations based on practical immunogold experiments. The theoretically deduced formula showed acceptable correlation to these calculations. This study gives a theory--expressed mathematically--for what is happening on the molecular level at the surface of resin sections in immunoelectron microscopy. The theory explains why acrylic resins normally are better suited for immunoelectron microscopy than epoxy sections, and indicates increased usefulness of epoxy sections when the diameter of the protein carrying the epitope decreases.

Mechanism for antigen detection on deplasticized epoxy sections

The purpose of this investigation was to explain why deplasticizing of epoxy sections gives higher immunogold labeling than non-deplasticizing. The methods used were the following: (1) Comparison of the ratio of immunogold labeling of deplasticized and non-deplasticized sections with gold particles of different sizes and comparison of this ratio with respect to sections of different thickness, (2) the tilt method (Brorson et al., 1994). Human kidney tissue with amyloid A depositions, human fibrin, and human pituitary tissue were embedded, sections were deplasticized on grids, treated with anti-Aa, anti-fibrinogen or anti-ACTH (ACTH = adrenocorticotropic hormone), and reembedded on grids. Indications of significant antibody penetration were found only at the periphery of structures (ACTH-vesicles). This penetration was about 30 nm. The ratios of immunogold labeling of deplasticized and non-deplasticized sections were approximately 2, 5 and 1 for amyloid, fibrin and ACTH, respectively, and were independent of the gold particle size. No significant differences of gold labeling were found between thicker and thinner deplasticized epoxy sections regardless the gold particle size. No significant differences of gold labeling between deplasticized epoxy sections and LR-White sections were found on interior areas of ACTH-vesicles or amyloid A plaques. The increased labeling of deplasticized epoxy sections compared to normal epoxy sections seemed to be mainly a surface phenomenon. The practical significance of this observation is that deplasticizing of epoxy sections may be a better method for localizing antigens at the periphery of structures than the use of other resin embedding media. Deplasticizing of epoxy sections may be a method of choice in a pathological laboratory to detect antigens in routinely embedded tissues.

Tumors of the endocrine/neuroendocrine system: an overview

For the sake of discussion, the markedly diversified tumors of the endocrine/neuroendocrine system are classified as those originating in classic epithelial endocrine organs (eg, adrenal cortical adenomas), from the diffuse endocrine cells (eg, jejunal carcinoid tumors), or from clusters of these cells (eg, islet cell tumors); and those arising from neurosecretory neurons (eg, neuroblastoma) or paraganglia (eg, carotid body tumor). Although traditional transmission electron microscopy is useful for identifying neurosecretory or endosecretory granules as such, with few exceptions (eg, insulin-containing granules with a complex paracrystalline core) it is not possible to ascribe a granule type (size, shape, or ultrastructure) to a distinct nosologic entity or secretory product because of their overlapping fine structures in different cell types. Immunoelectron microscopy methods utilizing colloidal gold-labeled secondary antibodies can be used to localize virtually any antigen (peptide or neuroamine) to a specific neurosecretory or endosecretory granule or other cell structure. General endocrine/neuroendocrine cell markers such as neuron-specific enolase, the chromogranins, and synaptophysin are useful in identifying neuroendocrine differentiation in a neoplasm using routine immunohistochemical procedures. The current relevance of the APUD concept of Pearse as well as the biologic importance of endocrine/neuroendocrine secretory products such as bombesin and insulinlike growth factors also are discussed.

Coexpression of insulin and somatostatin in single secretory granules of a pancreatic endocrine tumor

Pancreatic endocrine tumors, examined by immunohistochemistry, were found to be associated with multihormonal production, and recent studies, performed by employing double immunostaining methods, reported the coexpression of hormones in single cells or in single secretory granules. These findings have been attributed to the heterogeneity of the neoplastic cell population, characterized by the emergence of clones with different phenotypes, and were considered a sign of cell dedifferentiation or malignancy. In this study we describe a case of pancreatic endocrine tumor that showed focal colocalization of insulin and somatostatin in single secretory granules, by means of double labelling immunoelectron microscopy. We think that this observation can be linked to the hypothesis of those authors who speculated upon the appearance of polycrine cells in human fetal pancreas during embryogenesis.

Ultrastructural immunolabeling in the evaluation, diagnosis, and characterization of neuroendocrine neoplasms

Neuroendocrine neoplasia represents a heterogenous entity with variable morphologic light microscopic expressions. In many cases a definite diagnosis is easily made by light microscopic examination, but in some cases this does not suffice. In the latter instances, immunocytochemistry, ultrastructural examination, or both are required to diagnose a neuroendocrine neoplasm. However, basing a diagnosis of neuroendocrine neoplasia exclusively on the results obtained from immunocytochemical or ultrastructural evaluation of these tumors may not be entirely accurate in some instances. Ultrastructural immunolabeling plays a key role in accurately defining localization of immunoreactive substances in well-characterized neuroendocrine neoplasms, can assess colocalization of antigenic epitopes, helps define specificity and significance of immunocytochemistry results obtained at the light microscopic level, and is more sensitive than light microscopic immunocyto-chemistry. Some evolving diagnostic entities can be further characterized by utilization of ultrastructural labeling techniques. Controversies concerning the neuroendocrine nature of electron-dense structures identifiable at the ultrastructural level can be readily and accurately resolved. By providing a way to evaluate combined immunomorphologic parameters, ultrastructural immunogold labeling can settle important questions pertaining to neuroendocrine neoplasia. The present article illustrates a series of cases where the above-mentioned applications were tested.

Ultrastructural immunolabeling: a general overview of techniques and applications

Ultrastructural immunolabeling techniques combine the advantages of routine electron microscopy and detection of antigenic epitopes, the latter of which is customarily done by immunocytochemistry at the light microscopic level. In surgical pathology, immunocytochemistry has become routine to approach the differential diagnosis of difficult cases. Immunoelectron microscopy has been used primarily for research purposes or for addressing specific questions in diagnostic pathology. Ultrastructural immunolabeling is extremely useful in those instances in which the ultrastructural and immunocytochemical findings are not pathognomonic and are subject to interpretation. Preembedding and postembedding labeling techniques have been described in the literature. Preembedding techniques are not as applicable to diagnostic work, however. Their use remains rather limited to applications in which the antigen to be labeled cannot maintain its viability when exposed to fixatives. Even in such cases a new methodology--the LifeCell process--has emerged; this technique cryofixes tissues, thereby maintaining antigenic integrity. After cryofixation, a postembedding labeling technique can be utilized. Immunogold and peroxidase methods are used for labeling. Immunogold methods elegantly mark reaction sites with preservation of underlying morphology. Postembedding immunogold methods are used by most individuals working in the field. Ultrastructural labeling techniques are rapidly moving from classification as exclusively research tools to the diagnostic arena.

Plurihormonality in the secretory granules of the normal human pituitary. An immunoelectron microscopic study

Normal human autopsy anterior pituitary tissue from 5 cases was embedded in LR White resin and immunolabelled using silver-enhanced 5-nm protein A gold probes. Follicle stimulating hormone (FSH), thyroid stimulating hormone (TSH), luteinizing hormone (LH), adrenocorticotrophic hormone (ACTH), growth hormone (GH) and prolactin (PRL) were immunolocalised to the level of secretory granule. A two-sided double-labelling method was used to cross-react two hormones at a time with respect to their corresponding antibodies. All possible combinations of the six pituitary hormones were tested. Plurihormonal granules were found that contained LH + FSH, LH + TSH, and FSH + TSH. Each hormone was also found in monohormonal granules. Granule diameter was significantly larger in the pluri as opposed to monohormonal granules.

Differential silver enhanced double labeling in immunoelectron microscopy

A two-sided double labeling method using protein A gold was used to demonstrate the presence of two hormones within the same anterior pituitary cell granule. A single probe size was used for both section faces but one side of the grid was silver enhanced. The use of a single probe size reduced the cost of the study and eliminated the variations in labeling efficiency that result from the use of different probe sizes.

Ultrastructural and electron immunohistochemical features of medullary thyroid carcinoma

An ultrastructural study, both morphological and immunohistochemical, has been carried out on eight thyroglobulin-positive and nine thyroglobulin-negative medullary carcinomas of the thyroid. The morphometric analysis of granule size showed that all tumours contained cells with small granules and cells with medium size granules, whereas eight tumours had additional cells with large granules. The small granules had an electron dense core, while the medium and large sized granules were both pale-cored and dense-cored. The cells with small, medium or large secretory granules were all immunoreactive for calcitonin and CGRP. No ultrastructural differences were observed between thyroglobulin-positive and thyroglobulin-negative cases of medullary carcinoma of the thyroid.