New immunolatex spheres: visual markers of antigens on lymphocytes for scanning electron microscopy

Receptor-mediated adhesion phenomena. Model studies with the Radical-Flow Detachment Assay

Receptor-mediated cell adhesion phenomena play a vital role in many physiological and biotechnology-related processes. To investigate the physical and chemical factors that influence the cell/surface interaction, we have used a radial flow device, a so-called Radial-Flow Detachment Assay (RFDA). The RFDA allows us to make direct observations of the detachment process under specified experimental conditions. In results reported here, we have studied the detachment of receptor-coated latex beads (prototype cells) from ligand-coated glass surfaces. The receptors and ligands used in this work are complementary antibodies. The beads enable us to examine several aspects of the adhesion process with particles having uniform properties that can be varied systematically. Advantages of the RFDA are many, especially direct observation of cell detachment over a range of shear stresses with quantitative measurement of the adhesive force. We focus our studies on the effects of ligand and receptor densities, along with the influence of pH and ionic strength of the medium. These data are analyzed with a mathematical model based on the theoretical framework of Bell, G. I. (1978. Science [Wash. DC]. 200:618-627) and Hammer, D. A. and D. A. Lauffenburger (1987. Biophys. J. 52:475-487). We demonstrate experimental validation of a theoretical expression for the critical shear stress for particle detachment, and show that it is consistent with reasonable estimates for the receptor-ligand bond affinity.

Mapping neuronal inputs to REM sleep induction sites with carbachol-fluorescent microspheres

The cholinergic agonist carbachol was conjugated to latex microspheres that were fluorescently labeled with rhodamine and used as neuroanatomical probes that show little diffusion from their injection site and retrogradely label neurons projecting to the injection site. Microinjection of this pharmacologically active probe into the gigantocellular field of the cat pontine brain stem caused the awake cats to fall into rapid movement (REM) sleep indistinguishable from that produced by free carbachol. Three-dimensional computer reconstruction of the retrogradely labeled neurons revealed a widely distributed neuronal network in the pontine tegmentum. These pharmacologically active microspheres permit a new precision in the characterization and mapping of neurons associated with the control of behavioral state and of other cholinergic networks.

Optimized synthesis of polyglutaraldehyde nanoparticles using central composite design

A central composite design was applied to the optimization of the synthesis of polyglutaraldehyde nanoparticles (PGNP). The effects of monomer concentration, surfactant concentration, pH, oxygen level, and stirring rate on the particle size, polydispersity, surface carboxyl group concentration, and yield of PGNP were investigated. The optimal conditions for the synthesis of PGNP were found to be: 7% (w/v) glutaraldehyde, 2.5% (w/v) dextran, pH 12, 70% (v/v) oxygen, and a stirring rate of 1080 rpm. Under these conditions, the values of the dependent variables adequately resembled those predicted by the model. The usefulness of these particles in the targeted delivery of cytotoxic drugs is discussed.

A new immunoreagent for cell labeling. CD3 monoclonal antibody covalently coupled to fluorescent polymethacrylic nanoparticles

The preparation and application of immunonanospheres are described. CD3 monoclonal antibodies were covalently coupled to fluorescent polymethacrylic nanoparticles by the glutaraldehyde reaction and the resultant conjugate purified by gel filtration on a Sepharose 4B column. Peripheral blood mononuclear cells labeled with this immunoreagent were observed by both fluorescence microscopy and scanning electron microscopy in order to evaluate the technique.

Polymer microbeads in immunology

Synthetic polymer microbeads have been studied extensively and the required properties, including monodispersity and size range 0.05-10 microns can best be achieved by radiation polymerization based on methacrylate derivatives. Fluorochrome-conjugated beads can be used for cell surface markers and simultaneously to study phagocytosis. The paper reviews some of these applications. Cell separation techniques are also described. Future possibilities for immunological and cell biology studies are discussed.

Direct measurement of nanometric displacement under an optical microscope

A novel method has been developed to measure nanometric displacement under a conventional optical microscope. The magnified image of a pinhole was divided into two parts using a prism-shaped mirror. The difference of light intensity between the divided images was determined, which was proportional to displacementof the pinhole. Using a 5-microm diam pinhole, the accuracy to determine displacement was ~1 nm. Instead of a pinhole, polystyrene microbeads were used in the new method. Displacement of the microbeads was also measured with nanometric accuracy. This technique could be used to probe nanometric phenomena using optical microscopes.

Colloidal gold fluorescent microspheres: a new retrograde marker visualized by light and electron microscopy

A new retrograde tracer, rhodamine latex microspheres, permits labeled neurons to be visualized with fluorescence light microscopy. However, their use has been limited to the light microscope. We now have developed colloidal gold fluorescent microspheres which identify retrogradely labeled neurons first by fluorescence microscopy and then by electron microscopy. This new fluorescent/EM tracer will find widespread use in the field of neuroscience to elucidate the ultrastructural integrity of neuronal networks.

Flow cytometric quantitative evaluation of phagocytosis by human mononuclear and polymorphonuclear cells using fluorescent nanoparticles

The use of fluorescent polymethacrylic nanoparticles (0.3 micron) as a flow cytometric reagent in the quantitative evaluation of phagocytosis by human mononuclear and polymorphonuclear cells is described. The preparation of the nanoparticles, by emulsion copolymerization of methacrylic monomers, and their physicochemical properties are briefly summarized. Nanoparticles coupled with a fluorescent agent (ethidium bromide) were used in a flow cytometric assay to study opsonin-independent phagocytosis by human polymorphonuclear cells and by human monocytes. The phagocytosis of nanospheres by monocytes was determined by flow cytometry from the fluorescence distribution and ingestion was visualized by scanning and transmission electron microscopy. One possible application of the fluorescent nanoparticles is the simultaneous analysis of cell surface antigens and cell phagocytic activity.

Detection of chicken antibody to the protozoan parasite Eimeria tenella by antigen-coated microspheres

A sensitive immunoassay for detecting antibodies to the protozoan parasite of poultry Eimeria tenella, has been developed. Microspheres coated with parasite antigen are reacted with antibody-containing chicken serum followed by a fluorescent labeled second antibody and analyzed by flow cytometry. The assay was used to demonstrate that chickens, vaccinated with E. tenella sporozoite antigen, showed significant elevations in serum antibody levels after exposure to infection compared to non-vaccinates. The assay is reproducible and because antigen-coated microspheres are stable for up to 4 weeks at 4 degrees C, a single batch can be used to analyze multiple serum samples.

The IIb-IIIa glycoprotein complex that mediates platelet aggregation is directly implicated in leukocyte adhesion

Evidence is presented that the IIb-IIIa glycoprotein complex, which functions as the receptor for fibrinogen on platelets and is central to platelet aggregation, is expressed on the surface of leukocytes where it may function as a receptor for fibronectin. F(ab')2 fragments of a monoclonal antibody, 25E11, raised against activated large granular lymphocytes, inhibited killing by natural killer cells, blocked the binding of fibronectin-coated particles by monocytes, and stimulated neutrophils to exhibit increased antibody-dependent killing. Immunoprecipitation studies of leukocytes and platelets, and the ability of 25E11 to inhibit platelet aggregation, identified the antigen as an epitope on the IIb-IIIa complex. This glycoprotein thus constitutes the first example of a receptor mediating both platelet aggregation and leukocyte adhesion.

Rapid, high-yield purification of cell surface membrane using colloidal magnetite coated with polyvinylamine: sedimentation versus magnetic isolation

A new technique for the magnetic isolation of external plasma membrane from Dictyostelium discoideum is described and compared to a previously published procedure employing sedimentation of silica-coated plasma membrane. The magnetic isolation technique involves coating intact cells with a polyvinylamine-magnetite colloid and overcoating with polyacrylate to form a dense pellicle. The magnetite pellicle totally coated the cells and was not internalized. Coated cells were lysed and membrane fragments retrieved from the cell homogenate using a diverging field electromagnet. The membrane obtained in such a manner was analyzed for marker enzyme activity and cell surface label. The plasma membrane was obtained in high yield (42%) with an average purification of 8-fold. The polyvinylamine-magnetite pellicle shielded the external plasma membrane face to proteolysis by papain and pronase. It also acted as a barrier to alpha-methylmannoside in concanavalin A-carbohydrate competition studies.

Zwa antigen distribution on the human platelet: an electron microscope study using a colloidal gold labelled marker

We present the application of a new technique for visualizing surface antigen distribution patterns on intact platelets, treated with anti Zwa antibody, using colloidal gold labelled anti-human immunoglobulin as a marker. Platelets from Zwa negative and from both heterozygous and homozygous Zwa positive individuals were examined for surface Zwa antigen distribution. Platelets fixed with paraformaldehyde show an even distribution of gold particles with a well-developed reticular pattern over their surfaces. Platelets heterozygous for Zwa shows considerable antigen variation, some platelets having similar quantities of antigen to, others much less than, homozygotes. The importance of platelet fixation prior to antigen demonstration by anti Zwa antibody and immunogold visualization is seen by the redistribution of antigen on unfixed platelets. It is suggested that this technique could be exploited to investigate the relationship between platelet surface antigens or structures and their functions.

Basophil immunoglobulin receptors in asthmatics under immunoscanning electron microscopy

Immunolatex particles were used as markers for IgE receptors on basophils using electron-microscope scanning. These particles appeared to bind specifically to basophils. Basophils from atopic asthma patients showed greater binding to latex particles than those from intractable asthma patients or healthy subjects. Cap and patch formations on IgE receptors were frequently found in basophils of atopic asthmatics, and cap formation was observed only on basophils that were pear-shaped. The redistribution of IgE receptors, such as that by cap formation, may be a significant triggering mechanism for basophil activation. The latex density on basophils pre-treated with anti-human IgG was much greater in intractable asthmatics than in atopic asthmatics or healthy subjects, and almost all basophils with increased immunolatex particles were pear-shaped, suggesting the presence of some IgG receptors on the surface, and such receptors may play an important role in intractable asthma.

SEM localization of laminin on the basement membrane of the chick corneal epithelium with immunolatex microspheres

Embryonic chick corneal explants were soaked in mild detergent and the anterior corneal epithelium was peeled from its basement membrane, leaving the lamina lucida surface exposed and supported on the subjacent primary stroma. Explants were treated with rabbit anti-laminin IgG, followed by sheep anti-rabbit IgG linked microspheres, and processed for SEM. The lucida surface was heavily decorated with microspheres, whereas controls treated with preimmune rabbit IgG were essentially beadless. Laminin distribution was not regular, appearing denser in some regions than others. However, the connective tissue surface of the basement membrane was never laminin-positive, even after treatment with hyaluronidase. These results suggest the basal lamina of the corneal epithelium is asymmetric, with preferential location of laminin to the lucida surface of the basement membrane.

A novel approach for scanning electron microscopy of colloidal gold-labeled cell surfaces

A method is described for the use of scanning electron microscopy on the surface of gold-labeled cells. It includes the use of 45- or 20-nm colloidal gold marker conjugated with Staphylococcal protein A. The marker is best recognized on the basis of its atomic number contrast by using the backscattered electron imaging mode of the scanning electron microscope. When the backscattered electron signal is mixed with the secondary electron signal, an optimum correlation between the distribution of the labeled sites and the cell surface structures is demonstrated. The method is illustrated by its application to the identification of human circulating granulocytes. Its good resolution, high contrast, and good labeling efficiency offers a promising approach to the specific localization of cell surface antigenic sites labeled with particles of colloidal gold.

Microinjected fluorescent polystyrene beads exhibit saltatory motion in tissue culture cells

Microinjected 0.26-micron fluorescent, carboxylated microspheres were found to display classical saltatory motion in tissue culture cells. The movement of a given particle was characterized by a discontinuous velocity distribution and was unaffected by the activity of adjacent particles. The microspheres were translocated at velocities of up to 4.7 micron/s and sometimes exhibited path lengths greater than 20 micron for a single saltation . The number of beads injected into a cell could range from a few to over 500 with no effect on the cell's ability to transport them. Neither covalent cross-linking nor preincubation of the polystyrene beads with various proteins inhibited the saltatory motion of the injected particles. The motion of the injected beads in cultured cells was reversibly inhibited by the microtubule poison nocodazole, under conditions in which actin-rich, nitrobenzoxadiazol - phallacidin -staining structures remain intact. Whole-cell high voltage electron microscopy of microinjected cells that were known to be moving the fluorescent microspheres revealed that the beads were embedded in the cytoplasmic matrix and did not appear to be membrane bound. The enhanced detectability of the fluorescent particles over endogenous organelles and the ability to modify the surfaces of the beads before injection may enable more detailed studies on the mechanism of saltatory particle motion.

Ferritin conjugates as specific magnetic labels. Implications for cell separation

Concanavalin A coupled to the naturally occurring iron storage protein ferritin is used to label rat erythrocytes and increase the cells' magnetic susceptibility. Labeled cells are introduced into a chamber containing spherical iron particles and the chamber is placed in a uniform 5.2 kG (gauss) magnetic field. The trajectory of cells in the inhomogeneous magnetic field around the iron particles and the polar distributions of cells bound to the iron particles compare well with the theoretical predictions for high gradient magnetic systems. On the basis of these findings we suggest that ferritin conjugated ligands can be used for selective magnetic separation of labeled cells.

Separation of cells labeled with immunospecific iron dextran microspheres using high gradient magnetic chromatography

Immunospecific magnetic microspheres, consisting of ferromagnetic iron dextran conjugated to Protein A, were used to specifically label red blood cells (RBC) for cell separation studies using high gradient magnetic chromatography ( HGMC ). When 10(7)-10(8) RBC labeled with Protein A-iron dextran microspheres were applied to a column containing 30 mg stainless steel wire placed in a 7.5 kilogauss magnetic field, 96 +/- 2% of the cells were retained in the column. These cells could be eluted by removing the magnetic field and mechanically agitating the column. The retention of labeled cells by HGMC was shown to be dependent on the applied magnetic field and the amount of wire packed into the column. HGMC in conjunction with cell labeling with immunospecific iron dextran microspheres have useful applications for the separation of specific cell types.

Whole-cell-mount cytochemistry by the colloidal gold labeling method. Combined transmission and scanning electron microscopic study of ConA binding sites in mouse macrophages

Binding, redistribution, and endocytosis of colloidal gold (CG)-labeled concanavalin A (ConA) were studied by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Mouse peritoneal macrophages were cultured on Formvar-coated platinum grids. Either fixed or unfixed cells were labeled by the indirect ConA-CG labeling method. Specimens were critical-point-dried and observed by TEM and SEM in the same region. Surface-bound ConA-CG was easily seen by SEM. Stereomicroscopic observation by TEM clearly showed the three-dimensional distribution of ConA on the cell surface as well as in the cytoplasmic vesicles and vacuoles. In the prefixed cells, CG was distributed randomly on the cell surface. When unfixed cells were labeled at 0 degree C, a similar binding pattern was observed, although the density of bound CG was decreased. When cells labeled with ConA-CG at 0 degree C were further incubated at 37 degrees C, redistribution and endocytosis of the label were seen. Endocytosed CG in the cytoplasmic vesicles and vacuoles was clearly seen by TEM. In addition, three-dimensional location and relationship with other organelles were easily observed. Combined TEM and SEM observation of CG-labeled whole-cell-mount specimens is a useful method to study the dynamics of cell-bound ligands.

Polymeric microspheres for immunoresearch

New microspheres having functional aldehyde groups have been prepared by radiation polymerization of acrolein solution containing hydroxyethyl methacrylate and glutalardehyde. The size distribution in the microspheres was narrow and average particle diameter was 1 - 2 micron. The binding ability of the microspheres to antigen increased by increasing the concentration of glutalardehyde. The preparation procedure of the microspheres is simple. The microspheres can be used for immunoresearch.

Agarose-polyaldehyde microsphere beads: synthesis and biomedical applications. Cell labeling, cell separation, affinity chromatography, and hemoperfusion

Polyaldehyde microspheres, polyglutaraldehyde (PGL), and polyacrolein (PA) were synthesized by polymerizing glutaraldehyde and acrolein in the presence of an appropriate surfactant. The microspheres with average diameter of 0.2 micron were used for the specific labeling of human red blood cells (RBC) and mouse lymphocytes. The "naked" microspheres were encapsulated with agarose and formed agarose-polyaldehyde microsphere beads in sizes ranging from 50 microns up to 1 cm. The encapsulated beads, with diameters ranging from 50 to 150 microns were used as insoluble adsorbents for affinity purification of antibodies. Beads with diameters varied from 150 to 250 microns were used for cell fractionation purposes (mouse B splenocytes from T splenocytes). Uniform beads of 1 mm diameter were designed for hemoperfusion purposes. As a model, the removal in vitro of anti-BSA from immunized goat whole blood was studied.

A method for processing polymeric beads for critical point drying

Polymeric beads are increasingly being used for surface studies. Processing of these beads for critical point drying (CPD) poses a problem since these beads must be handled in suspension. For this processing, a method has been described here which relies on a capsule made by an ordinary micropipette tip covered on the end by parafilm and on the other by a filter paper which permits the exchange of fluid without the loss of beads.

The selective detection of cell surface determinants by means of antibodies and acetylated avidin attached to highly fluorescent polymer microspheres

Procedures are described for the synthesis of 500 A-diameter polymer microspheres containing a novel fluorescent cross-linking agent. These microspheres have very high fluorophore concentration without quenching of the fluorescence and show very low nonspecific interaction with cells. When monoclonal anti-Thy-1.2 is attached to the fluorescent microspheres, specific binding results in 10(4) spheres being attached per thymocyte while non-specific binding is less than 1%. Similar values are obtained for an indirect staining procedure. The high non-specific binding of cationic avidin to negative cell surfaces is shown to be decreased to negligible levels by acetylation of the amine groups of the protein without decreasing its high-affinity binding to biotin. The use of acetyl-avidin (pI = 6.7) directly, or when attached to fluorescent microspheres, resulted in a highly selective detection of biotinyl groups on the erythrocyte or lymphocyte cell surface. Attachment of biotinyl groups to the hinge carbohydrates of antibodies did not affect their specificity. It allowed their detection by means of microspheres-acetyl-avidin conjugates.

Novel effective immunoadsorbents based on agarose-polyaldehyde microsphere beads: synthesis and affinity chromatography

Agarose-polyaldehyde microsphere beads were produced by encapsulating polyacrolein microspheres or polyglutaraldehyde microspheres with agarose. Magnetic beads were formed by carrying out the encapsulation procedure in the presence of ferrofluidic particles. Proteins were bound covalently, at physiological pH, to the beads through their aldehyde groups to produce the Schiff base products. The conjugates, beads-proteins, were used successfully in affinity chromatography for specific purification of antibodies. Leaching of the proteins bound to the beads under physiological conditions and eluting conditions was not detected. The agarose-polyaldehyde microsphere beads are suggested as alternatives to the supports currently used in affinity chromatography.

Immunoperoxidase labeling of Streptococcus mutans for scanning electron microscopy

The application of an immunoperoxidase method to labeling of Streptococcus mutans subsp. sobrinus for scanning electron microscopy is described. Bacteria from four separate cultures were fixed in 2.5% buffered glutaraldehyde solution. The specimens were treated in accordance with an indirect immunolabeling procedure using a rabbit anti-S. mutans subsp. sobrinus gamma-globulin. Labeled bacteria were equipped with a layer of small, distinct globules of horse-radish peroxidase reaction product. Bacteria exposed to control incubations were not equipped with this layer.

Development of a latex-conjugated immunocytological marker for scanning electron microscopic analysis of quail-chick chimeras

Quail-chick chimeras are created by transplanting pieces of quail tissue to chick. We have used antibodies combined with a cell surface marking technique [modified after Molday et al.('75)], to facilitate scanning electron microscopic (SEM) identification of quail cells in such chimeras. First, antibodies to quail RBCs were raised in rabbits by intravenous injection. Rabbit anti-quail RBC serum was precipitated by ammonium sulfate, purified by DEAE chromatography, and cross-absorbed with chicken RBCs. Second, sheep anti-rabbit IgG was purchased commercially and further purified by affinity chromatography. Third, 900-A-diameter latex beads were synthesized by aqueous emulsion copolymerization of methacrylates. Spheres were bound with diaminoheptane to create an extension arm which was further derivatized in a two-step glutaraldehyde procedure. Purified sheep IgG was bound to the aldehyde-activated spheres, with uncoupled sheep IgG removed by sucrose density centrifugation. To test the marker, rabbit anti-quail IgG was added to 1% diluted quail RBCs. After washing, sheep anti-rabbit IgG bound spheres were introduced. Washed cells were fixed in one-half strength Karnovsky's and processed for SEM. Quail RBCs were uniformly decorated with beads, containing 2,000 beads per cell. Similarly treated chick RBCs show no binding to beads. Likewise, quail RBCs not pre-treated with the rabbit IgG do not bind beads. Prefixed quail RBCs still bind latex-conjugated beads, although at somewhat reduced levels. When mixtures of quail and chick RBCs were processed for identification: (1) sphere labeling was an "all or none" phenomenon; (2) the proportion of bead-decorated cells observable in the SEM was the same as the proportion of quail RBCs provided in the initial mix; and (3) morphologically distinguishable embryonic chick RBCs did not label whereas under the same conditions, quail RBCs do. We further demonstrate that rabbit antibodies prepared by injection of stage 4 quail primitive streaks can be used to specifically label quail epiblast and mesoblast cells, providing markers for at least two germ layers. It is now possible to combine grafting techniques of known success, with SEM analysis of the chimera.

Immunospecific ferromagnetic iron-dextran reagents for the labeling and magnetic separation of cells

Ferromagnetic iron dextran particles were prepared by reacting a mixture of ferrous chloride and ferric chloride with dextran polymers under alkaline conditions. Particles purified by gel filtration chromatography were in the size range of 30-40 nm, had an electron dense core of about 15 nm, were stable against aggregation in physiological buffer, showed little non-specific binding to cells and had a magnetic moment. Protein A from Staphylococcus aureus was covalently coupled to periodate-oxidized ferromagnetic iron-dextran particles. These conjugates were used to indirectly label antigen sites on human red blood cells and thymocytes for visualization by scanning and transmission electron microscopy. Cells labeled with these immunospecific ferromagnetic particles are were quantitatively retained by a simple permanent magnet and could be separated from unlabeled cells. Applications of these novel reagents in the separation of cells, cell membranes and receptors in drug targeting studies are discussed.

Application of Light Scattering to Polymers, Liquid Crystals, and Biological Systems

The applications of elastic and quasielastic light scattering techniques to polymers in dilute solution, thermotropic liquid crystals and biological membrane vesicles are presented. It is focused on how we extract specific structural features or dynamic processes of these condensed medium samples through the light scattering methods. The paper reviews the light scattering studies that were carried out at the author's laboratory in Wisconsin from 1973 until 1980.

Membrane asymmetry. A survey and critical appraisal of the methodology. I. Methods for assessing the asymmetric orientation and distribution of proteins

This and the companion article are aimed at surveying the methods used for the study of membrane asymmetry. The techniques employed for the assessment of the asymmetric distribution and orientation of membrane proteins are reviewed in this article, whereas those pertaining to the unequal distribution of lipids are detailed in the companion paper. The use of immunological techniques and lectins, functions of proteins and their perturbations, chemical reagents, enzymatic isotopic labeling and enzymatic cleavage of membrane proteins and physical techniques are discussed and illustrated using recent examples of their application. Whenever appropriate, problems involving crypticity and non-availability or non-reactivity of functional sites, relevant chemical functions or protein fragments to appropriate ligands, reagents or modifying enzymes are envisaged and possible modification of the exposure of proteins during preparation of ghosts and other drawbacks are discussed, the use of different techniques and control experiments in conjunction is recommended for a more realistic assessment of the distribution and orientation of proteins.

Receptor binding and internalization of immobilized transcobalamin II by mouse leukaemia cells

Membrane transport of vitamin B12 (cyanocobalamin; Cbl) into mammalian cells is mediated by the serum protein transcobalamin II (TCII). In mouse leukaemia L1210 cells, TCII-Cbl binds to membrane receptors in a rapid, temperature-independent step and is internalized by a slow, temperature-dependent process. To delineate the location of receptors on these cells, we have constructed a visual probe by covalently coupling purified TCII-Cbl to submicrometre latex particles (minibeads). We report here that when L1210 cells are incubated with minibeads containing TCII-Cbl at 4 degrees C and examined by scanning electron microscopy (SEM), the particles are found attached predominantly to microvilli. Incubation of the cells at 37 degrees C results in the internalization of the minibeads. As visualized by transmission electron microscopy (TEM), this endocytotic process seems to occur in clathrin-coated pits and vesicles at the cell surface.

Polar differences of delayed and implanting mouse blastocysts in binding of Alcian Blue and concanavalin A

Mouse blastocysts in delay of implantation and after an 18-hour activation for implantation by estrogen were recovered by flushing with glutaraldehyde containing Alcian Blue or by flushing with cold Dulbecco's PBS containing 0.1% sodium azide for further processing according to an Alcian Blue technique and a ConA-latex technique, respectively. Blastocysts in delay of implantation showed no or only faint staining with Alcian Blue, while blastocysts activated for 18 hours displayed a marked staining of the abembryonic pole. Binding of ConA-latex spheres demonstrated a markedly higher density at the abembryonic end of both delayed and implanting blastocysts. It is concluded that, as demonstrated by the Alcian Blue technique, the abembryonic trophoblast, which is the first one to attach and invade at implantation, has changed the properties of the extracellular coat, probably in a way that favors increase of adhesiveness and invasiveness. The similarity in pattern of ConA binding of both delayed and implanting blastocysts, however, suggests that this property is related more to preimplantational differences in proliferative activity of the two poles than to implantatory changes.

Immunocytochemical localization of intracellular antigens with SEM

A method for the localization of intracellular antigens with a scanning electron microscope using peroxidase-labelling antibodies is described. A search for a hydrogen donor which may be deposited at the sites of antigen by enzymatic action and emit secondary electrons or generate backscatter electrons was made. It was found that when 4-chloro-1-naphthol was used, the peroxidase deposited reaction product which resulted in a strong secondary electron emission at the site of antigen. With this method, the presence of luteinizing hormone in secretion granules and other cytoplasmic structures of gonadotropic cells was demonstrated. The level of detection of intracellular antigens with this method is not as high as that detectable with light microscopical examination of the same specimens, that is, more reaction product at the site of antigen is required to be detectable with scanning electron microscopy than with light microscopy. In spite of the lack of high sensitivity, the intracellular antigens may be localized with the method described.