Use of colloidal gold particles in double-labeling immunoelectron microscopy of ultrathin frozen tissue sections

Immunoperoxidase methods for the localization of antigens in cultured cells and tissue sections by electron microscopy

We have presented our detailed methods for localizing antigens in cultured cells and tissue sections by IP at the EM level. Immunoperoxidase cytochemistry is particularly well suited for the study of sparse antigens as a result of the enzymatic amplification afforded by the method, and of molecules confined within a membrane-enclosed compartment wherein the DAB reaction produce can accumulate. Although IP is commonly used to localize membrane-compartmentalized molecules, reliable qualitative information can also be obtained on cytoplasmic antigens as well (Anderson et al., 1978; Merisko et al., 1986; Rodman et al., 1984). For these and other reasons, it is likely that IP cytochemistry will continue to be an important tool for the cell biologist especially in the study of membrane traffic. Other inventive combinations of immunocytochemical methods will likely be forthcoming, for example, combining IP localization with postembedding labeling by colloidal-gold conjugates to provide triple EM labeling.

Immunocytochemical localization and biochemical analysis of alpha and beta keratins in the avian lingual epithelium

The alpha and beta keratins are found as 10-nm and 3-nm cytoplasmic filaments, respectively. While the alpha keratins are produced in essentially all vertebrate epithelia (Franke et al.: Exp. Cell Res., 116:429-445, 1978; Sun et al.: Proc. Natl. Acad. Sci. USA, 76:2813-2817, 1979), the beta keratins have been demonstrated only in specific epithelial tissues of birds and reptiles (Sawyer et al.: In: Biology of the Integument: Vertebrates. J. Bereiter-Hahn, A.G. Matoltsy, and K.S. Richards, eds. Springer-Verlag, Berlin, Vol. 2, pp. 194-238, 1986; Landmann: In: Biology of the Integument: Vertebrates. J. Bereiter-Hahn, A.G. Matoltsy, and K.S. Richards, eds. Springer-Verlag, Berlin, Vol. 2, pp. 150-187, 1986). Recently, Homberger and Brush (Zoomorphology, 106:103-114, 1986) have demonstrated that within the lingual epithelium of parrots, beta keratins are expressed exclusively in the anterior ventral region. While it is well established that epidermal-dermal interactions are important for the regional expression of the beta keratin genes in the avian scutate scales and feathers, little is known about the expression of beta keratins in other epithelial structures such as the tongue. We have used biochemical and immunocytochemical techniques to analyze the alpha and beta keratins of the lingual epithelium of the chick as an initial step in the characterization of this model system for developmental studies. We have found that alpha keratins are present throughout the lingual epithelium. The anterior ventral epithelium contains alpha keratin polypeptides characteristic of skin-type differentiation, while the epithelium of the dorsal and posterior ventral regions contains alpha keratin polypeptides characteristic of esophageal-type differentiation (O'Guin et al.: In: Current Topics in Developmental Biology: The Molecular and Developmental Biology of Keratins. A.A. Moscona and A. Monroy, eds. R.H. Sawyer, vol. ed. Academic Press, New York, Vol. 22, pp. 282-306, 1987). Beta keratins are produced only in the differentiated epithelial cells of the anterior ventral region of the tongue. Immunoelectron microscopy demonstrates that the alpha and beta keratins of the stratum intermedium and corneum of the anterior ventral region are found together in the large filament bundles characteristic of this region. The preexistence of the alpha keratins in the cells destined to produce beta keratins as well as the colocalization of these keratins in the filament bundles of these cells suggests that a functional relationship may exist between the alpha and beta keratins.

Prevention of non-specific interactions of gold-labeled reagents on tissue sections

The protein A-gold technique is amongst the most useful labeling techniques available for light and electron microscopic immunolabeling. Some electron microscopic studies, however, have suggested that protein A-gold, and other protein-gold complexes as well, may bind non-specifically to certain tissue structures, particularly in skin, creating a specious pattern of labeling. We utilized the protein A-gold technique with antiserum to both involucrin and keratin under a variety of conditions to document the specificity of labeling. When the standard conditions were followed, the protein A-gold technique produces highly specific results. These conditions include: 1. the blocking of unreacted aldehyde groups by amination; 2. the blocking of non-specific binding sites on tissue sections by preincubation with inert proteins; and 3. the use of proper concentration of the protein A-gold complex. However, non-specific labeling could be produced if the three components of the standard protocol were omitted. In particular, the use of too concentrated protein A-gold lead to non-specific labeling. We report here also updated working protocols for antigen detection with protein A-gold on semithin Lowicryl K4M and paraffin sections which provide optimal staining results.

Ultrastructural localization of dentine phosphoprotein in rat tooth germs by immunogold staining

Dentine phosphoprotein (DPP) was localized on thin frozen sections of fixed rat tooth germs by indirect immunogold staining. Antisera were directed against DPP and against glutaraldehyde-treated DPP and were characterized by immuno-electroblotting. In odontoblasts, DPP was found to be localized in the cisternae of the rough endoplasmic reticulum (RER) and the Golgi apparatus and in Golgi-associated vesicles. Odontoblastic processes were moderately positive for DPP and dentine was intensely labeled on frozen sections of unfixed tissue. Predentine showed a slight immunoreactivity. These results indicate the synthesis of DPP in the RER, its accumulation in the Golgi apparatus and its vesicular transport and secretion via the odontoblastic processes into dentine. The close association of the gold particles with the dentinal collagen fibres makes a role of DPP in linking mineral to collagen conceivable. Matrix vesicles were negative for DPP, suggesting that the protein is not present at the sites of matrix vesicle-associated nucleation.

Sorting of mannose 6-phosphate receptors and lysosomal membrane proteins in endocytic vesicles

The intracellular distributions of the cation-independent mannose 6-phosphate receptor (MPR) and a 120-kD lysosomal membrane glycoprotein (lgp120) were studied in rat hepatoma cells. Using quantitative immunogold cytochemistry we found 10% of the cell's MPR located at the cell surface. In contrast, lgp120 was not detectable at the plasma membrane. Intracellularly, MPR mainly occurred in the trans-Golgi reticulum (TGR) and endosomes. lgp120, on the other hand, was confined to endosomes and lysosomes. MPR was present in both endosomal tubules and vacuoles, whereas lgp120 was confined to the endosomal vacuoles. In cells incubated for 5-60 min with the endocytic tracer cationized ferritin, four categories of endocytic vacuoles could be discerned, i.e., vacuoles designated MPR+/lgp120-, MPR+/lgp120+, MPR-/lgp120+, and vacuoles nonimmunolabeled for MPR and lgp120. Tracer first reached MPR+/lgp120-, then MPR+/lgp120+, and finally MPR-/lgp120+ vacuoles, which are assumed to represent lysosomes. To study the kinetics of appearance of endocytic tracers in MPR-and/or lgp120-containing pools in greater detail, cells were allowed to endocytose horse-radish peroxidase (HRP) for 5-90 min. The reduction in detectability of MPR and lgp120 antigenicity on Western blots, due to treatment of cell homogenates with 3'3-diaminobenzidine, was followed in time. We found that HRP reached the entire accessible pool of MPR almost immediately after internalization of the tracer, while prolonged periods of time were required for HRP to maximally access lgp120. The combined data suggest that MPR+/lgp120+ vacuoles are endocytic vacuoles, intermediate between MPR+/lgp120-endosomes and MPR-/lgp120+ lysosomes, and represent the site where MPR is sorted from lgp120 destined for lysosomes. We propose that MPR is sorted from lgp120 by selective lateral distribution of the receptor into the tubules of this compartment, resulting in the retention of lgp120 in the vacuoles and the net transport of lgp120 to lysosomes.

Ultrastructural studies on calcitonin gene-related peptide-, tachykinins- and somatostatin-immunoreactive neurones in rat dorsal root ganglia: evidence for the colocalization of different peptides in single secretory granules

Calcitonin gene-related peptide (CGRP)-, tachykinins- and somatostatin-immunoreactive neurones in rat dorsal root ganglia have been studied by means of single and double immunogold labelling techniques. Peptide-immunoreactive neurones are generally B- or C-type cells of small size, with well developed rough endoplasmic reticulum and scanty neurofilaments. In neurones classifiable as A2-type cells, i.e. larger neurones with a lighter cytoplasm due to the presence of poorly developed Nissl bodies and numerous neurofilaments, only CGRP immunoreactivity was detected. Immunolabelled structures were identified as large (60-100 nm diameter), electron-dense, membrane-bounded p-type granules. They were observed only in neuronal cell bodies or in the intraganglionic portions of the axons. No granules immunoreactive to the antisera applied in this study were observed in non-neuronal cells. Immuno-staining experiments with different combinations of the antisera revealed, in some cells, the presence of double immunolabelled granules; in particular localization of CGRP and tachykinins, CGRP and somatostatin, and tachykinins and somatostatin to single secretory granules was demonstrated. The finding that more than one peptide is localized to the same secretory granule supports the postulate that peptides are co-released upon nerve stimulation providing morphological support for physiological and pharmacological data demonstrating an interaction between different peptides in the modulation of synaptic activity.

An immunoelectron microscopic study of glucocerebrosidase in type 1 Gaucher's disease spleen

An immunogold labeling procedure was applied to ultrathin cryosections and used to study the subcellular localization of glucocerebrosidase in lipid-laden "Gaucher cells" in spleen from a patient with type 1 Gaucher's disease. Glucocerebrosidase protein was associated with the characteristic stored lipid material in large, irregularly shaped vacuoles. As shown by double labeling, the storage vacuoles contained not only glucocerebrosidase protein but also other lysosomal enzymes. Thus the storage vacuoles can be considered to be secondary lysosomes. The findings indicate that although glucocerebrosidase was present in secondary lysosomes in this patient, the activity of the mutant enzyme was insufficient to prevent storage of glucocerebroside in the spleen.

The major protein of pancreatic zymogen granule membranes (GP-2) is anchored via covalent bonds to phosphatidylinositol

GP-2, the major integral protein characteristic of the pancreatic zymogen granule membrane can be released from the membrane by the action of a phosphatidylinositol specific phospholipase C (PI-PLC). In a hydrophobic/hydrophilic phase separation system using the non-ionic detergent Triton X-114, the membrane-bound form of the protein went from the detergent phase into the hydrophilic phase upon action of the phospholipase. PI-PLC solubilization of GP-2 unmasked an antigenic determinant similar to the cross-reacting determinant of the trypanosome variant surface glycoproteins. This determinant being a distinctive feature of the glycan moiety of phosphatidyl-inositol anchored membrane proteins, it established the glycosyl-phosphatidyl-inositol nature of the GP-2 membrane anchor. Since soluble GP-2 is also found in the contents of the granule and is secreted intact into the pancreatic juice, it is likely that one of the mechanisms responsible for its release could be a specific phospholipase. GP-2 is the first glycosyl-phosphatidyl-inositol-anchored protein that is integral to the membrane of an organelle and not located at the surface of the cell.

Identification of molecules in the kidney utilizing immunocytochemistry

Immunocytochemistry of the kidney is a unique method to integrate physiology, biochemistry, and molecular biology with morphology. Both mono- and polyclonal antibody reagents are useful and each has advantages and disadvantages. Specificity with low background is of the greatest importance. Tissue preparation techniques depend on the antigen being studied as well as the methodology to be used. Pre- and postembedding techniques combined with visualization with peroxidase reaction products or with particulate markers such as ferritin and gold must be chosen for each individual circumstance to be studied. Important applications in the kidney have included studies of glomerular antigens, specific transport proteins, and segment-specific antigens of unknown specificity. Future utilization of this technique with new molecular probes will greatly enhance our knowledge of the biology of the kidney.

Immunogold-EM localization of actin and vimentin filaments in relation to polygonal arrays in lens epithelium in situ

An indirect immunogold technique for transmission electron microscopy was used for localizing two cytoskeletal proteins, actin and vimentin, in the epithelium of freshly removed rabbit lens, especially in relation to the polygonal array structures located at the apices of the epithelial cells. Antibody specificity was determined on semi-pure chicken breast muscle actin and bovine lens vimentin using Western blotting of these proteins and extracts of rabbit lens epithelium separated by SDS-PAGE. Whole lenses of rabbits were lightly fixed in glutaraldehyde and embedded in LR White resin. Tangential sections were taken at 70 to 80 nm and at 0.25 micron and used for single-labeling, and double-labeling with antibodies raised in different hosts and treated with appropriate second antibodies conjugated with non-overlapping sizes of gold particles. Routine and stereomicroscopy were used to analyze gold-label patterns. The study shows that the rays of the polygons project deeply into the cell from the vertices lying on the inner apical membrane. Actin is located on the filaments of rays, but vimentin is not associated with the polygons at the level in the cell that we studied. Vimentin filaments are found in deeper regions of the epithelial cell. Stereopairs were useful in differentiating where the gold-label was located and in fact, this technique demonstrated that most of the label is on the surface of sections where the filaments are exposed.

Microwave-stimulated incubation in immunoelectron microscopy: a quantitative study

Microwave irradiation has been applied to reduce the immunogold staining time of ultrathin sections of Lowicryl embedded specimens. Labelling has been stimulated by microwave irradiation during incubation with 10 nm colloidal gold particles coated with either goat anti-mouse antibodies (GaM-gold) or goat anti-rabbit antibodies (GaR-gold) and has been compared with control incubations. Quantification has been performed on cytoplasmic membranes or lysosomes labelled with a primary antibody. Counting the gold particles over specific and non-specific sites in electron micrographs and electron microscopic images by IBAS 2000 revealed that irradiation of 25 microliters droplets both at 80 W and 150 W resulted in an accelerated immunogold labelling, while the non-specific background levels were not increased. A plateau level in immunogold labelling intensity was reached after 25 min incubation under microwave irradiation at 150 W as compared to 120 min incubation without microwaves. No improvement in localization sharpness of immunogold labelling on membranes was achieved by microwave irradiation. The microwave-mediated acceleration of immunogold staining may be considered as an example of a staining method with a restricted thermal action on microvolumes as indicated by direct temperature measurements using a fibre-optic thermometer.

Isolation of a fragment of tau derived from the core of the paired helical filament of Alzheimer disease

A substantially enriched preparation of Alzheimer paired helical filaments (PHFs) has been used as a starting point for biochemical studies. Pronase treatment, which strips off adhering proteins, leaves a resistant core that is structurally intact. This has been used to raise a monoclonal antibody that decorates the filament core. The antibody has been used to follow the extraction of two peptide fragments (9.5 and 12 kDa) by immunoblotting. The link between the PHF as a morphological entity and these peptides has been established independently by photoaffinity labeling with a chemical ligand to the PHF core. Sequence analysis of these peptides was used to design oligonucleotide probes for cloning a cognate cDNA, which leads to its identification as human microtubule-associated tau protein. The sequencing of the 9.5- and 12-kDa peptides shows they are derived from a conserved region of tau containing three repeating segments. Since these fragments have been copurified with the Pronase-resistant core and are only released by subsequent steps, the corresponding part of the tau molecule must be tightly bound in the PHF core.

Improving the stability of a foreign protein in the periplasmic space of Escherichia coli

An efficient expression/export vector comprising the entire phoS (phosphate binding protein) gene fused to a synthetic gene encoding the human growth hormone releasing factor (mhGRF) has recently been constructed [1]. The hybrid protein (PhoS-mhGRF) was exported to the periplasmic space. However, in this location proteolytic degradation occurred at the C-terminal region. Phenylmethylsulfonyl fluoride (PMSF) increased the stability of the hybrid protein indicating that a serine protease may be involved in the proteolytic cleavage. The correct export and subsequent degradation of the recombinant protein in the periplasmic space were demonstrated in situ using double immunogold labeling on ultrathin sections. Using a phoS-based expression/export vector in the presence of PMSF, 2-4 mg of hybrid protein per liter of culture could be obtained.

The pathways of endocytosed transferrin and secretory protein are connected in the trans-Golgi reticulum

We used a conjugate of transferrin and horseradish peroxidase (Tf/HRP) to label the intracellular transferrin receptor route in the human hepatoma cell line HepG2. The recycling kinetics of [125I]Tf/HRP were similar to those of unmodified [125I]Tf, implying identical routes for both ligands. 3,3'Diaminobenzidine (DAB)-cytochemistry was performed on post-nuclear supernatants of homogenates of cells which were incubated with both Tf/HRP and [125I]Tf, and caused two different effects: (a) the equilibrium density of [125I]Tf containing microsomes in a Percoll density gradient was increased, and (b) the amount of immunoprecipitable [125I]Tf from density-shifted lysed microsomes was only 20% of that of nonDAB treated microsomes. The whole biosynthetic route of alpha 1-antitrypsin (AT), a typical secretory glycoprotein in HepG2 cells, was labeled during a 60-min incubation with [35S]methionine. DAB cytochemistry was performed on post-nuclear supernatants of homogenates of cells which were also incubated with Tf/HRP. DAB cytochemistry caused approximately 40% of microsome-associated "complex" glycosylated [35S]alpha 1-antitrypsin ([35S]c-AT) to shift in a Percoll density gradient. Only part of the density shifted [35S]c-AT could be recovered by immunoprecipitation. A maximum effect was measured already after 10 min of Tf/HRP uptake. The density distribution of the "high mannose" glycosylated form of 35S-alpha 1-anti-trypsin [( 35S]hm-AT) was not affected by Tf/HRP. If in addition to Tf/HRP also an excess of non-conjugated transferrin was present in the medium, [35S]c-AT was not accessible for Tf/HRP, showing the involvement of the transferrin receptor (TfR) in the process. Furthermore, we show that if Tf/HRP and [35S]c-AT were located in different vesicles, the density distribution of [35S]c-AT was not affected by DAB-cytochemistry. Pulse-labeling with [35S]methionine was used to show that [35S]c-AT became accessible to endocytosed Tf/HRP minutes after acquirement of the complex configuration. A common intracellular localization of endocytosed Tf/HRP and secretory protein could be confirmed by immuno-electron microscopy: cryosections labeled with anti-albumin (protein A-colloidal gold) as well as DAB reaction product showed double-labeling in the trans-Golgi reticulum.

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

Several double gold-labeling methods have been reviewed, and our own results of applying some of these methods have been included. Of the six double-staining methods tested, four gave satisfactory results (indirect double immunogold staining method, two-face protein A-gold staining method, two-face amplified protein A-gold staining method, and formaldehyde blockade protein A-gold staining method). The other two techniques (sequential double protein A-gold staining method and formaldehyde blockade amplified protein A-gold staining method) showed cross-reaction between the first and second staining sequence.

The role of ultrastructural investigations in neurotoxicology

The ways in which ultrastructural approaches have been applied to the investigation of xenobiotic-induced toxicity of the nervous system have been briefly reviewed. These approaches have been grouped in 3 broad areas, viz. morphology, function and composition. Firstly, morphological approaches permit the visualisation of changes in intercellular relationships, the identification of the subcellular target(s) of a xenobiotic substance and the discrimination between what may appear ostensibly to be identical cellular responses to one or more chemically distinct toxins. Secondly, functional approaches using, e.g. cytochemistry, ion precipitation, immunocytochemistry and autoradiography provide indications of metabolic state, the identity or the intra- or extracellular location of the "reactive species". Thirdly, those approaches, viz. electronprobe X-ray microanalysis and electron energy loss spectroscopy which provide information of the elemental composition of cells and tissues permit an assessment of the subcellular distribution and compartmentalisation of endogenous substances and toxic or therapeutic xenobiotics. In concert, ultrastructural approaches possess the ability to contribute unique information on the effects of exposure of cells of the nervous system to toxic substances and so direct further investigation towards an understanding of the mechanism of action.

Bacterial antigen immunolabeling in macrophages after phagocytosis and degradation of Bacillus subtilis

After phagocytosis of Bacillus subtilis 168 by bone marrow-derived macrophages, the intracellular pathway followed by different antigens was studied by immunofluorescence and immunoelectron microscopy. Three different rabbit antisera were used: (i) an antiserum to B. subtilis whole cells mainly recognizing the cell wall constituents, (ii) an antiserum to teichoic acid, and (iii) an antiserum to peptidoglycan recognizing the disaccharide tetrapeptide molecules resulting from peptidoglycan degradation. During the first 3 h after phagocytosis of B. subtilis, the three antisera were confined to the same vacuolar compartments, as follows. They were first found in phagosomes gathered in the perinuclear region. Upon bacterial degradation, the three antisera colocalized in an increasing number of small dense vesicles, located in the perinuclear region, that seemed to result from the fragmentation of phagolysosomes. These vesicles correspond to an acidic compartment since they also stained for 3-(2,4-dinitroanilino)-3'-amino-N-methyldipropylamine, a drug known to accumulate in the acidic compartments of cells. At later time points, the antigens recognized by the three antisera followed different pathways. After 18 h, teichoic acid and peptidoglycan were no longer detectable in macrophages whereas an antigen(s) labeled with antiserum to B. subtilis whole cells remained stocked for several days in small acidic vesicles randomly distributed throughout the macrophage. This compartment appeared to be different from the one labeled during the first 3 h after ingestion of bacteria. These results suggest that the transport rate and the compartments implicated in antigen processing differ according to the antigen.

Structural studies of nerve terminals containing melanin-concentrating hormone in the eel, Anguilla anguilla

Eels were adapted to black- or white-coloured backgrounds and the pituitary glands were prepared for light and electron microscopy. Immunocytochemical staining was used to study the distribution of the neurohypophysial melanin-concentrating hormone in the neurointermediate lobe. The hormone was located in small, elliptical, electron-opaque neurosecretory granules, measuring approximately 120 x 90 nm. The neurones terminated on blood vessels in the centre of the neurohypophysis and on the basement membrane separating neural and intermediate lobe tissues. The results of both light and electron immunocytochemistry and of radioimmunoassay are consistent with a higher rate of hormone release from eels adapted to white backgrounds than from those adapted to black backgrounds. In addition to this, when fish that had been adapted to white tanks were transferred to black tanks, there was an accumulation of irMCH in the gland and an increased numerical density of secretory granules at nerve terminals. These results reinforce the proposal that MCH is released during adaptation to a white background, to cause melanin concentration and to inhibit MSH release, and that its release is halted in black-adapted fish.

Intracellular colocalization of variant surface glycoprotein and transferrin-gold in Trypanosoma brucei

Endocytosis and intracellular transport has been studied in the bloodstream forms of Trypanosoma brucei by light and electron microscopy, using colloidal gold coupled to bovine transferrin (transferrin-gold). The endocytosed transferrin-gold, visualized by silver intensification for light microscopy, was present in vesicular structures between the cell nucleus and flagellar pocket of the organism. At the ultrastructural level, transferrin-gold was present after a 10-min incubation in the flagellar pocket, coated vesicles, cisternal networks, and lysosomelike structures. Endocytosis and intracellular processing of T. brucei variable surface glycoprotein (VSG) was studied using two preparations of affinity-purified rabbit IgG directed against different parts of the VSG. One preparation of IgG was directed against the cross-reacting determinant (CRD): a complex glycolipid side chain covalently linked to the COOH-terminus of the VSG molecule. The other was directed against determinants on the rest of the VSG molecule. When the two IgG preparations were used on thawed, thin cryosections of trypanosomes that had been incubated in transferrin-gold before fixation, the organelles involved with transferrin-gold endocytosis labeled with both antibodies, as well as many vesicular, tubular, and vacuolar structures that did not contain endocytosed transferrin-gold. Both antibodies also labeled the cell surface. In double-labeling experiments both antibodies were closely associated except that IgG directed against the VSG molecule labeled all the cisternae of the Golgi apparatus, whereas anti-CRD IgG was shown to label only half of the Golgi apparatus. Evidence for sorting of VSG molecules from endocytosed transferrin-gold was found. Double-labeling experiments also showed some tubular profiles which labeled on one side with anti-CRD IgG and on the other side with anti-VSG IgG, suggesting a possible segregation of parts of the VSG molecule.

The cellular effects of estrogens on neuroendocrine tissues

Estrogen action on sensitive neurons in the rat diencephalon has been studied by morphologic techniques; evidence of estrogen action at every level is presented, including tracts, cells, circuitry and subcellular organelles. The demonstration in the arcuate nucleus of estrogen-induced synaptic remodelling, estrogen-induced postsynaptic membrane phenotypes, changes in intracellular membranes and rapid estrogen actions on neuronal endo-exocytosis indicates that cellular estrogen actions may underlie the neuronal control of reproduction.

Detection of cell surface antigens in tissue sections by means of pre-embedding immunogold staining

The immunogold technique has been used in electron microscopy to detect cytoplasmic and extracellular antigens by postembedding techniques. It has also been used to detect plasma-membrane-associated molecules on suspended cells and, recently, to visualize cell surface antigens in ultrathin sections of Lowicryl embedded specimens. In the present study, cell surface antigens of rat kidney and human skin were identified in tissue sections by using pre-embedding immunogold labeling. Brush border microvillar antigens and dermal lymphocyte antigens both bound numerous gold particles. The immunogold staining described here has the advantage over immunoperoxidase procedures that is not subject to diffusion or reabsorption artifacts, and allows estimation of the antigen density on labeled cells. Furthermore, this pre-embedding immunogold technique is ideally suited to detecting cell surface-associated antigens since it preserves antigenicity, allows gold particle penetration and enhances cell membrane profiles.

Antibody competition studies with gold-labelling immunoelectron microscopy

Competitive studies, involving neutralizing monoclonal antibodies (NTmAbs) to outercoat proteins of Akabane virus were performed by immunoelectron microscopy. The experiments were designed to determine whether the NTmAbs were directed against the same or spatially different epitopes. Characteristics of NTmAbs in direct and indirect gold-labelling studies were determined. It was found that the protein A method gave cross-contamination of the immuno-gold complexes whereas direct conjugation of the NTmAbs to gold probes gave clean, specific and intense labelling. Analysis of dilution curves confirmed that saturation of antigenic sites did not occur and secondly determined the optimum working dilutions for the conjugated probes. The data generated in the preliminary studies enabled reliable results to be obtained from the double-labelling competitive experiment. We found that the 2 NTmAbs were directed to either the same epitope or to 2 separate but neighbouring epitopes where the binding of one NTmAb inhibited the binding of the second. The results demonstrate that if reliable data is to be obtained in double-labelling immunoelectron microscopical studies then experiments must be meticulously designed.

Ultrastructural localization of osteocalcin in rat tooth germs by immunogold staining

Osteocalcin was localized by indirect immunogold staining of thin frozen sections of rat tooth germs which had been fixed by different methods. Acrolein fixation proved to be satisfactory considering the preservation of fine structure and antigenicity. In odontoblasts, osteocalcin was found to be localized in the cisternae of the rough endoplasmic reticulum and Golgi apparatus. Few positive transport vesicles were found. Staining for osteocalcin in odontoblastic processes was only observed after strong fixation and was intense in odontoblasts engaged in early dentine formation. Predentine was slightly positive in the neighbourhood of positive processes. Matrix vesicles were negative and strong osteocalcin labeling of dentine seemed to appear after the onset of mineralization.

Ultrastructural localization of steroid sulphatase in cultured human fibroblasts by immunocytochemistry: a comparative study with lysosomal enzymes and the mannose 6-phosphate receptor

Immunocytochemistry was used to study the subcellular localization of steroid sulphatase in cultured human fibroblasts. Ultra-thin cryosections were incubated with antibodies raised against steroid sulphatase purified from human placenta and immune complexes were visualized with gold probes as electron dense markers. Steroid sulphatase was found in rough endoplasmic reticulum, Golgi cisternae and in the trans-Golgi reticulum, where it co-distributes with lysosomal enzymes and the mannose 6-phosphate receptor. The enzyme was not detected in lysosomes. Steroid sulphatase was also found at the plasma membrane and in the endocytic pathway (i.e. coated pits, endosomes and multivesicular endosomes). These may be the sites where sulphated oestrogen precursors are hydrolysed. Also here, it co-localizes with lysosomal enzymes and the mannose 6-phosphate receptor. It is concluded that microsomal steroid sulphatase and lysosomal enzymes share several cellular compartments.

Sorting of three secretory proteins to distinct secretory granules in acidophilic cells of cow anterior pituitary

The distribution of three proteins discharged by regulated exocytosis--growth hormone (GH), prolactin (PRL), and secretogranin II (SgII)--was investigated by double immunolabeling of ultrathin frozen sections in the acidophilic cells of the bovine pituitary. In mammotrophs, heavy PRL labeling was observed over secretory granule matrices (including the immature matrices at the trans Golgi surface) and also over Golgi cisternae. In contrast, in somatotrophs heavy GH labeling was restricted to the granule matrices; vesicles and tubules at the trans Golgi region showed some and the Golgi cisternae only sparse labeling. All somatotrophs and mammotrophs were heavily positive for GH and PRL, respectively, and were found to contain small amounts of the other hormone as well, which, however, was almost completely absent from granules, and was more concentrated in the Golgi complex, admixed with the predominant hormone. Mixed somatomammotrophs (approximately 26% of the acidophilic cells) were heavily positive for both GH and PRL. Although admixed within Golgi cisternae, the two hormones were stored separately within distinct granule types. A third type of granule was found to contain SgII. Spillage of small amounts of each of the three secretory proteins into granules containing predominantly another protein was common, but true intermixing (i.e., coexistence within single granules of comparable amounts of two proteins) was very rare. It is concluded that in the regulated pathway of acidophilic pituitary, cell mechanisms exist that cause sorting of the three secretory proteins investigated. Such mechanisms operate beyond the Golgi cisternae, possibly at the sites where condensation of secretion products into granule matrices takes place.

Regulatory peptide immunocytochemistry at light- and electron microscopical levels

Immunocytochemical techniques applied at both light- and electron microscopical levels are valuable in the study of regulatory peptide distribution in normal and diseased tissue, whether in the form of sections or whole cell preparations. Successful immunolocalization depends on adequate preservation of the peptide antigen and the tissue structure in which it resides; a suitably specific and sensitive labelled antibody detecting system. In general, peptides are stable molecules, most of which retain their antigenicity after conventional cross-linking fixation and tissue processing, allowing standard immunocytochemical methods to be used for light- and electron microscopy. Regulatory peptides are derived from precursor molecules and several 'families' of structurally similar peptides are now generally recognised. Region-specific antibodies may be needed to overcome problems of cross-reactivity or to identify a bioactive form in the presence of its precursor. Multiple co-localisation of different related and unrelated peptides in the same cell or even storage granule is now recognised and can be identified by immunocytochemistry.

Membranes of sorting organelles display lateral heterogeneity in receptor distribution

This study describes the distribution of an intrinsic membrane protein, the asialoglycoprotein receptor (ASGP-R) in the trans-Golgi reticulum and compartment of uncoupling receptor and ligand (CURL) of rat liver cells. Using quantitative immunogold electron microscopy and membrane length measurements, we showed lateral nonhomogeneity of receptors in the membranes of trans-Golgi reticulum and CURL, in particular in the membranes of secretory vesicles (identified by their content of albumin and very low density lipoprotein particles) and of CURL vesicles (endosomes), including multivesicular bodies. The characteristic tubulovesicular morphology of both sorting organelles defines the transition of receptor-rich tubular membrane and the receptor-poor limiting membrane of the attached vesicles. There was a direct relationship between the size of the secretory and CURL vesicles and the density of ASGP-Rs in their membranes. Receptor density in the smallest vesicles was similar to that found in adjacent continuous tubules. The larger the vesicles, the less receptor was detectable in their membranes. We propose that the receptor molecules are excluded from the vesicle membranes by dynamic lateral redistribution. Nonrandom receptor distribution in the CURL vesicle membranes was present even at the multivesicular body stage. These observations strongly suggest the existence of barriers to ASGP-R diffusion at the junctions of tubules and vesicles. In addition, our observations suggest that ASGP-Rs are transported to the plasma membrane via a mechanism other than the normal secretory pathway.

Binding sites of Ulex europaeus-lectin I in human parotid gland. A light-microscopic and ultrastructural study using the immunoperoxidase technique and immunocryoultramicrotomy

Twenty non-neoplastic parotid glands (removed during neck dissection for regional tumours) were examined for cellular and subcellular binding sites of Ulex europaeus-lectin I (UEA-I), a lectin reported to be specific for alpha-L-fucose. For light microscopy, an extended peroxidase-antiperoxidase method was applied; for the evaluation of the subcellular localization of bound lectin, three of these glands were examined following immunocryoultramicrotomy and staining by the protein A-gold technique. In addition to the known cytoplasmic affinity of UEA-I for capillary endothelium, acinar cells bound the lectin within the cytoplasmic compartment; the number and distribution of stained acinar cells varied among individuals. Furthermore, cytomembrane-bound labelling that occurred most markedly at the luminar surface was observed in striated-duct epithelium. Using the electron microscope, protein A-gold particles were seen in zymogen granules and in Golgi cisternae of serous acinar cells; primary saliva secreted in the lumina exhibited strong labelling; serous acinar cells had binding sites on their cell membranes, striated-duct epithelium had binding sites on its surface membrane and in the vicinity of apical vesicles. Our results show that UEA-I is a useful tool for the study of the structure and functional states of the parotid gland epithelium and its associated pathological alterations.

Novel type of proliferating lymphoplasmacytoid cell with a characteristic spotted immunofluorescence pattern

We examined bone marrow from myeloma patients for the presence of cells with the characteristics of the clonogenic cell in the myeloma stem cell assay. We identified a novel type of cell that contained cytoplasmic immunoglobulin of the relevant idiotype located in a cytoplasmic spot. This "spotted" Ig could be located in the rough endoplasmic reticulum. Spotted cells are highly proliferative, as evidenced by the nuclear staining with the antibody Ki67, and were found in the bone marrow from most of the myeloma patients studied. This type of cell was also present in patients with immunocytomas, in some cases of benign monoclonal gammopathy, and in patients in the state of polyclonal hypergammaglobulinemia. IgG subclass distribution of so-called spotted cells and plasma cells, found in a patient with pseudo biclonal gammopathy, indicates that spotted cells are intermediate between B cells and plasma cells. Spotted cells express the B cell-associated antigens HB4 and HB6 but do not express other B cluster of differentiation antigens or plasmacytoid antigens tested.

Schistosoma mansoni: immunogenic glycoproteins of the cercarial glycocalyx

Immunochemical studies at the level of the light and electron microscope showed that a monoclonal antibody, 128C3/3, was directed to an epitope in the glycocalyx of Schistosoma mansoni cercariae. Immunoprecipitation of surface labeled cercarial extracts with this monoclonal antibody demonstrated that the glycocalyx is composed of at least five components, including a very large molecular size polypeptide and polypeptides of 220, 180, 170, and 15 kDa. After transformation of cercariae to schistosomula, these polypeptides were shed from the surface and were therefore no longer accessible to surface labeling. Monoclonal antibody 128C3/3 was also reactive with a 38 kDa polypeptide from schistosomula; this polypeptide was weakly expressed on the surface of cercariae. Analysis of immunoprecipitates of radioiodinated protein extracts of cercariae, newly transformed schistosomula, and 36 hr in vitro cultured schistosomula showed that the 180 and 170 kDa polypeptides continued to be expressed within the organism following transformation, but were not accessible to surface labeling. Lectin binding studies revealed differences in the oligosaccharide composition of the six polypeptides. With the exception of the 15 kDa antigen, all the polypeptides reactive with 128C3/3 were highly immunogenic in infected mice and humans.

Serotyping and electron microscopy studies of Staphylococcus aureus clinical isolates with monoclonal antibodies to capsular polysaccharide types 5 and 8

Monoclonal antibodies to Staphylococcus aureus capsular polysaccharide types 5 and 8 were prepared and used to serotype 821 clinical isolates of S. aureus from four countries. The capsular polysaccharide-binding sites on the bacterial membrane were examined by transmission and scanning electron microscopy.

Immunogold cytochemistry of cytochromes P-450 in porcine adrenal cortex. Two enzymes (side-chain cleavage and 11 beta-hydroxylase) are co-localized in the same mitochondria

In order to study the distribution of mitochondrial cytochromes P-450 in porcine adrenal glands, the glands of anesthetized pigs were fixed in situ. Polyclonal antibodies against two cytochromes P-450, i.e., C27 side-chain cleavage enzyme and 11 beta-hydroxylase, were used to study the distribution of these enzymes in cryosections of the adrenal cortex. Ultrathin cryosections were evaluated by both protein-A/gold/silver immunocytochemistry and immunoelectron microscopy using double labeling with protein-A/colloidal-gold. At light microscopy, the two cytochrome P-450 enzymes were found to be broadly distributed in both the fasciculata and glomerulosa zones of the adrenal cortex. Quantitative immunoelectron microscopy revealed that both enzymes were localized only in mitochondria, in which they were present on the inner aspects of the inner mitochondrial membrane. Both cytochromes P-450 were demonstrable in all of the mitochondria examined, and statistical evaluation of the ratios of the two enzymes present in individual mitochondria yielded a normal distribution curve. Since no evidence was found for the preferential localization of either enzyme in a special population of mitochondria, we conclude that all mitochondria of the adrenal cortex contain both enzymes. We discuss implications of these findings with respect to the regulation of steroidogenesis.

Simultaneous demonstration of two antigens in ultrathin cryosections by a novel application of an immunogold staining method using primary antibodies from the same species

A recently developed immunocytochemical double-staining method for ultrathin Epon and Lowicryl K4M sections has been adopted for use on ultrathin cryosections. The essential features of the method include: staining for the first antigen by the indirect method using sufficient concentrations of second antibodies conjugated to colloidal gold particles to saturate available epitopes on the primary antibodies; supporting the cryosections by methyl cellulose followed by paraformaldehyde vapour treatment (30-60 min at 80 degrees C); removal of the methyl cellulose followed by staining for the second antigen using primary antiserum from the same species and another size class of colloidal gold particles conjugated to second antibodies. Contaminating staining does not occur if the paraformaldehyde vapour treatment exceeds 30 min, as this treatment destroys the combining sites on the second antibodies applied in the first staining cycle. Successful double-staining was documented using primary rabbit antibodies to growth hormone and corticotropin and anti-rabbit IgG conjugated to 5 and 15 nm colloidal gold particles. Following double-staining, the ultrathin cryosections may be silver-enhanced to improve detectability of the markers at low magnification.

Ultrastructural localization of glucocerebrosidase in cultured Gaucher's disease fibroblasts by immunocytochemistry

The subcellular localization of glucocerebrosidase was studied in cultured skin fibroblasts from eight patients with Gaucher's disease. The enzyme, in situ, was visualized under the electron microscope by incubating ultrathin frozen sections of fibroblasts with antibodies against glucocerebrosidase, followed by a second incubation with goat anti- (rabbit IgG) coupled to colloidal gold. In control cells, most of the gold label was found in lysosomes, associated with the membrane. Labelling of the rough endoplasmic reticulum (RER) and Golgi complex was also observed. In fibroblasts from three Gaucher's disease patients without neurological symptoms (type 1 disease), a near normal amount of cross-reactive material (CRM) was detected in lysosomes, but in a fourth such patient, the lysosomal CRM was reduced. Little lysosomal glucocerebrosidase was detected in cells from patients with the acute neuronopathic form (type 2) or the subacute neuronopathic form (type 3) of Gaucher's disease. CRM in lysosomes correlates with amount of mature, 59 kDA glucocerebrosidase which is undetectable in type 2 and type 3 Gaucher's disease cell lines. These findings demonstrate that different mutations in the gene for glucocerebrosidase result in mutant proteins that have different intracellular localizations. They also suggest that there is a relationship between the amount of cross-reactive material in the lysosomes and the phenotypic expression of the disease.

Detection of elastin by immunoelectronmicroscopy. A comparison of different procedures

Elastin components have been identified in chick aorta by different immunoelectronmicroscopic procedures (peroxidase-antiperoxidase, immunoferritin and immunogold) using affinity purified antibodies to chick tropoelastin. The PAP method used in a preembedding procedure stained the outer portion of amorphous elastin and the microfibrils very intensively. The surface of the cells was also slightly stained. On the contrary immunogold labelling on Epon or Lowicryl embedded sections produced a strong decoration only of amorphous elastin, while microfibrils remained almost completely unlabelled. The result is not due to loss of antigenicity of microfibrils during embedding, since similar data were obtained with immunoferritin in a preembedding procedure. Experiments performed under different stringency conditions showed that the products of the peroxidase reaction diffuse and redistribute in the tissue, indicating that the positive staining of microfibrils and cell surface is an artifact. The value of different immunological reagents and procedures in studying the fine mapping of elastin components is discussed.

Biochemical and immunochemical characteristics of the major protein of the murine parotid-granule membrane

The membrane fraction (ParB) of the secretory granules of mouse parotid gland was isolated and characterized. The major phospholipids were phosphatidylcholine and sphingomyelin. The membranes contained one major protein, PMC, constituting at least 30 per cent of the total protein. PMC was purified: it is a small acidic protein with molecular weight of 12,000, containing one residue of phosphate per molecule. Using anti-PMC serum, PMC was detected only in the mouse parotid and saliva. Immunochemical characterization of organelle fractions indicated that PMC was mainly present in the secretory granule fraction; it was in part tightly bound to granule membranes. PMC was also present in both the 100,000 g parotid-tissue supernatant and the water-extract of the ParB granules. This dual localization was corroborated by immunofluorescent studies with anti-PMC serum which demonstrated that PMC was distributed uniformly over the acinar cells. The major protein component of these membranes is absent from other exocrine organs, e.g. pancreas, submandibular and sublingual glands.

Lysosomal localization of secretory prostatic acid phosphatase in human hyperplastic prostate epithelium

The ultrastructural localization of secretory prostatic acid phosphatase (PAP) in human benign prostate tissue was accomplished using the immunogold technique on ultrathin Lowicryl sections. Polyclonal antibodies directed against secretory PAP (MW 50 kD) and the lysosomal enzymes alpha-glucosidase and beta-galactosidase as well as an antiserum directed against prostatic antigen (PA) were used. PAP was found in secretory vacuoles of columnar secretory epithelial cells. In addition, double labeling experiments revealed that secretory PAP was also localized in electron-dense organelles of columnar epithelial cells containing alpha-glucosidase and beta-galactosidase. PA was exclusively found in secretory vacuoles of columnar secretory epithelial cells. The results demonstrate the presence of secretory PAP within functional lysosomes and secretory vacuoles of the prostatic columnar epithelial cells and the absence of such PAP-containing lysosomes in the basal cells of the prostatic acini.

Epitopes of apolipoprotein B-100 and B-48 in both liver and intestine. Expression and evidence for local synthesis in recessive abetalipoproteinemia

The presence of apolipoprotein (apo) B in liver and intestine from a patient with abetalipoproteinemia was evaluated by immunohistochemistry with a polyclonal and six monoclonal antibodies to different apo B-48 and B-100 epitopes. In normal liver, apo B was present inside and outside hepatocytes. The patients liver exhibited staining in the cytoplasm with the polyclonal and three monoclonal antibodies. By immunoelectron-microscopy, apo B was found to be present in the smooth endoplasmatic reticulum and the Golgi complex. Normal intestinal epithelium was labeled with polyclonal and all monoclonal antibodies, including those specific for apo B-100. The patients epithelium stained with polyclonal and six monoclonals, and apo B was present in the Golgi complex. Thus, normal intestinal mucosa expressed apo B-48 and B-100 epitopes, which indicates apo B-100 synthesis in the gut. The synthesis of the apo B molecule in the patient seems to be retained in both liver and gut, which suggests a posttranslational defect.

The architecture of actin filaments and the ultrastructural location of actin-binding protein in the periphery of lung macrophages

A highly branched filament network is the principal structure in the periphery of detergent-extracted cytoskeletons of macrophages that have been spread on a surface and either freeze or critical point dried, and then rotary shadowed with platinum-carbon. This array of filaments completely fills lamellae extended from the cell and bifurcates to form 0.2-0.5 micron thick layers on the top and bottom of the cell body. Reaction of the macrophage cytoskeletons with anti-actin IgG and with anti-IgG bound to colloidal gold produces dense staining of these filaments, and incubation with myosin subfragment 1 uniformly decorates these filaments, identifying them as actin. 45% of the total cellular actin and approximately 70% of actin-binding protein remains in the detergent-insoluble cell residue. The soluble actin is not filamentous as determined by sedimentation analysis, the DNAase I inhibition assay, and electron microscopy, indicating that the cytoskeleton is not fragmented by detergent extraction. The spacing between the ramifications of the actin network is 94 +/- 47 nm and 118 +/- 72 nm in cytoskeletons prepared for electron microscopy by freeze drying and critical point drying, respectively. Free filament ends are rare, except for a few which project upward from the body of the network or which extend down to the substrate. Filaments of the network intersect predominantly at right angles to form either T-shaped and X-shaped overlaps having striking perpendicularity or else Y-shaped intersections composed of filaments intersecting at 120-130 degrees angles. The actin filament concentration in the lamellae is high, with an average value of 12.5 mg/ml. The concentration was much more uniform in freeze-dried preparations than in critical point-dried specimens, indicating that there is less collapse associated with the freezing technique. The orthogonal actin network of the macrophage cortical cytoplasm resembles actin gels made with actin-binding protein. Reaction of cell cytoskeletons and of an actin gel made with actin-binding protein with anti-actin-binding protein IgG and anti-IgG-coated gold beads resulted in the deposition of clusters of gold at points where filaments intersect and at the ends of filaments that may have been in contact with the membrane before its removal with detergent. In the actin gel made with actin-binding protein, 75% of actin-fiber intersections labeled, and the filament spacing between intersections is consistent with that predicted on theoretical grounds if each added actin-binding protein molecule cross-links two filaments to form an intersection in the gel.(ABSTRACT TRUNCATED AT 400 WORDS)

Post-embedding cytochemistry with gold-labelled reagents: a review

The detection of antigens and glycoconjugates with the protein A-gold and the lectin-gold techniques, respectively, is reviewed. Special attention is directed to the necessary conditions for fixation and embedding as well as to the staining procedures of tissue sections for light and electron microscopy.