An improved immunocytochemical method for subcellular localization of serotonin in rat enterochromaffin cells

Serotonin-like immunoreactivity (5-HT-LI) has been localized at the ultrastructural level in enterochromaffin (EC) cells of rat gastrointestinal tract. Ultra-thin sections of tissues embedded in epoxy resin were incubated with 5-HT antisera and antibody binding sites were visualized with protein A-gold. Three different antisera were compared and were shown to require different fixation regimens for optimal preservation of 5-HT-LI. For one antiserum, tissues fixed in glutaraldehyde and osmium tetroxide could be used to demonstrate 5-HT-LI in EC cells. Immunocytochemical localization of 5-HT can thus be performed with good ultrastructural preservation of tissues. Quantitative evaluation of the intracellular distribution of 5-HT-LI was performed on EC cells from antrum, duodenum, and proximal colon, fixed in glutaraldehyde only. In all three locations, the majority of the gold particles (90%) in EC cells were localized over the dense core of the secretory granules, while a minor fraction (10%) were localized in parts of the cytoplasm devoid of granules. In EC cells fixed in glutaraldehyde and post-fixed in osmium tetroxide, 5-HT-LI was reduced by about 85%, although intracellular distribution was essentially the same as in cells fixed in glutaraldehyde alone. The results indicate that 5-HT in EC cells is stored mainly in secretory granules, with a small fraction of 5-HT being localized outside the granules.

Determination of ABO blood groups by radioimmunoassay using 125I-protein A

Since the crystallizable fragment (Fc) portion of the immunoglobulin G (IgG) molecule is the binding site of Protein A, a radioimmunoassay procedure using 125I-Protein A was developed for identification of the ABO blood groups. The isotope level bound to Group A, B, or AB red cells decreased with the dilution of anti-A or -B, respectively. After sensitization by anti-A plus B in Group O serum, the isotope bindings were observed in Groups A, B, and AB cells, while no significant radioactive count appeared in Group O cells. Furthermore, there was little significant isotope binding in both Group A and B red cells sensitized by the serum from Group A or B blood containing mainly IgM anti-A or -B. A radioimmunoassay using 125I-Protein A is an excellent method for identifying ABO blood groups.

[Use of immunoenzyme analysis employing a staphylococcal protein A conjugate with peroxidase in the serodiagnosis of influenza]

A test-system was developed on the basis of solid-phase enzyme-immunoassay using protein A/peroxidase conjugate for the determination of antibody levels to influenza virus in sera of humans who had experienced a natural infection or received a live influenza vaccine. The accurate observation of the test conditions was demonstrated to give the results well correlating with those of the HI test. The use of isolated hemagglutinin as the antigen considerably increased the specificity of the enzyme-immunoassay and in a number of cases detected a 4-fold or higher rise of antibody titres to hemagglutinin in paired sera of the vaccinees where the HI test showed no rise in antibody titres.

Immunogold staining of microtubules in resting and activated platelets

A circumferential microtubule is known to support the discoid form of resting platelets, but its fate following exposure of the cells to aggregating agents is uncertain. The present study has employed an immunocytochemical approach to follow the fate of the circumferential microtubule in activated platelets. Monoclonal antibodies to tubulin and to vinculin and a polyclonal antibody to actin were incubated with isolated microtubule coils and stained with staphylococcal protein A coupled to immunogold in order to test their specificity. Thin sections of glycolmethacrylate embedded platelets before and after exposure to thrombin for 15, 30 and 60 s were stained with antibodies to tubulin and actin. Immunogold particles showed a high specificity for isolated MT coils stained for tubulin, modest intensity for actin, and none for vinculin. Gold particles were randomly distributed in thin sections of resting and activated platelets stained for actin. Immunogold was limited to the circumferential microtubule in resting platelets and constricted coils in thrombin-activated cells. The number of gold particles in areas of cytoplasm away from microtubules in platelets stained with antitubulin antibody increased slightly following thrombin activation, but the change was not significant. Results support the concept that microtubule coils supporting the discoid form of resting platelets do not dissolve following exposure of the cells to potent agonists.

Detection and identification of plant viruses by ELISA using crude sap extracts and unfractionated antisera

A simple and rapid procedure of enzyme immunoassay (PTA-ELISA) was used to detect and identify viruses in individual plants. Virus antigen in crude leaf extracts was adsorbed directly to a solid-phase support, allowed to react with unfractionated antiserum and the antigen-antibody complex detected with a general purpose conjugate of protein A and enzyme. Viral antigens were trapped most effectively by high bonding polystyrene microtitre plates loaded with leaf extracts prepared in carbonate buffer at pH 9.6. With protein A-alkaline phosphatase conjugate and the substrate p-nitrophenyl phosphate as the antibody-detection system, 18 plant viruses in 8 virus groups were detected reliably and nonspecific reactions did not occur. However, when the substrate 3,3',5,-tetramethyl benzidine was used in conjunction with protein A-horseradish peroxidase conjugate, nonspecific reactions were given by leaf extracts from some uninfected or virus-infected plant species. Where less sensitivity is required than is provided by versions of ELISA that rely on antibody-captured antigen, this method provides a simple and rapid means of detecting and identifying viruses in crude sap extracts with the aid of unfractionated antisera.

Immunocytochemical localization of cathepsins B and H in rat liver

Light and electron microscopic localization of cathepsins B and H in rat liver was investigated by immunoenzyme and protein A-gold techniques. For light microscopy (LM), semi-thin sections of the Epon-embedded material were stained by the immunoenzyme technique after removal of epoxy resin. For electron microscopy (EM), ultra-thin sections of the Lowicryl K4M-embedded material were stained by the protein A-gold technique. By LM, reaction deposits for cathepsins B and H were present in the cytoplasmic granules of parenchymal cells and endothelial cells, and Kupffer cells. The sinus-lining cells and the parenchymal cells showed the similar staining intensity. By EM, gold particles were present exclusively in lysosomes of all the cell types cited above. The same results were obtained from quantitative analysis. In addition, Golgi complexes themselves were mostly negative but some small vesicles on the trans side of them were labeled for these proteinases. The results indicate that cathepsins B and H are present in the lysosomes of rat liver and that these enzymes seem to be transported by small vesicles from endoplasmic reticulum to lysosomes via tubuloreticular network of the trans Golgi region.

Comparative sensitivity of 125I-protein A and enzyme-conjugated antibodies for detection of immunoblotted proteins

Immunoblotting is a powerful technique for the detection of small amounts of immunologically interesting proteins in unpurified preparations. Iodinated protein A (PA) has been widely used as a second antibody for detection of proteins; however, it does not bind equally well to immunoglobulins from different species nor does it bind to all subclasses of immunoglobulin G (IgG). We compared the sensitivity of [125I]PA with those of both horseradish peroxidase-conjugated second antibodies (HRP) and glucose oxidase-anti-glucose oxidase (GAG) soluble complexes for visualizing bovine serum albumin, human IgG, or human C3 which was either dot blotted or electroblotted to nitrocellulose. [125I]PA was uniformly 10- to 100-fold less sensitive than either HRP or GAG. GAG was more sensitive than HRP except for C3 (electroblotting) and bovine serum albumin and IgG (dot blotting), in which they were equivalent. In general, dot blotting was 10- to 1,000-fold more sensitive than electroblotting. Although relative sensitivities varied depending on the proteins analyzed and the antisera used, GAG appeared to be superior to [125I]PA and HRP for detection of immunoblotted proteins.

Postembedding immunoelectron microscopy using protein A-gold

Immunogold techniques offer the advantage of identifying antigens in tissues that show optimal ultrastructural morphology. The technique is applicable to any antigen that can be shown to withstand the denaturizing effects of fixation, osmication, dehydration, and embedding in epoxy resin. The list of antigens that survive these procedures is long and growing.

Ultrastructural immunolocalization of elastic fibers in rat blood vessels using the protein A-gold technique

Identification of elastic fibers at the ultrastructural level is accomplished by a post-embedding immunohistochemical technique using the protein A-colloidal gold method. Antisera against elastins from human dermis and rat aorta have been characterized by radioimmunoassay and then applied to thin sections of rat blood vessels. Two fixative solutions and two embedding media have been tested. Both antibodies bind to elastic fibers of normal arteries and veins, indicating crossreactions among organs and species. The high sensitivity of this method is demonstrated by its application to the detection of neo-elastogenesis in the intimal thickening of aortic grafts.

Enzyme linked protein-A: an ELISA for detection of amoebic antibody

Enzyme linked protein-A was used to develop an enzyme linked immunosorbent assay (ELISA) system for the detection of circulating antibodies to amoebic antigen. The specificity of protein-A to bind IgG only through Fc receptors, makes the test more specific for the detection of IgG antibodies to amoebic antigen. The ELISA system was used to detect amoebic antibody in control subjects (56), patients with amoebic liver abscess (79) and Entamoeba histolytica cyst-passers (10) and the results compared with those of indirect haemagglutination assay (IHA). The ELISA was more sensitive and detected 74.7% of cases with amoebic antibody in amoebic liver abscess compared with 66.7% detected by IHA. The test was more specific, sensitive and easy to perform and is recommended as a test of choice for the serological diagnosis of amoebic liver abscess.

Regional distribution of Sindbis virus glycoproteins on the plasma membrane of infected baby hamster kidney cells

Sindbis virus-infected baby hamster kidney (BHK) cells were analysed in surface replicas or conventional thin sections after specific immunolabelling with antiviral glycoprotein antibodies in conjunction with colloidal gold-conjugated protein A. Newly synthesized viral glycoproteins were detected, beginning 1 1/2 h after infection, while the virus maturation started 3 h after infection. The glycoproteins appeared to be inserted on the plasma membrane in large spots located mainly in the central area of the cells: no clustering of the labelling was detected. Later, the glycoproteins appeared to arrange linearly in regions in the medial portion of the cells. No labelling was found in the peripheral area or on the cell edges. A drastic change in the surface labelling was detected following the commencement of virus maturation: gold particles were organized mostly in small clusters, each labelling a budding virus. Very few glycoproteins appeared not to be involved in budding figures. The maturation of the virus was clearly regionalized, but during this time it also involved the peripheral area and the cell edges; preferential budding in narrow cellular processes was often observed. It appeared thus that either isolated glycoproteins soon after infection, or clustered glycoproteins at later times, are strictly regionalized on the plasma membrane: however, the early post-infection distribution is clearly different from that seen later during virus maturation. Our experiments support the concept of discrete plasma membrane domains even in cells that do not display distinct specialization of their surface.

Immunoelectron microscopic study of glomerular lesions using a postembedding method with a protein A-gold complex

Renal biopsy tissue from 33 children with various glomerular diseases has been investigated by electron microscopy using a postembedding immunostaining technique with a protein A-gold complex in order to establish more precise correlations between immunopathologic and morphologic findings in glomeruli. This technique could detect immunoglobulins (IgG, IgA, and IgM), complement factor (C3c), and fibrinogen-related antigen. The immunoreactivity of these antigens was essentially confined to the mesangial, paramesangial, subendothelial, and subepithelial 'electron-dense deposits' in the glomeruli. Except for IgM and C3c in the case of glomerular sclerosis, the distribution of the mentioned factors was even in the electron-dense deposits, as could be shown by 'double-immunolabeling'. From the above-mentioned findings one can conclude that several of the localized factors are associated with the formation of electron-dense deposits, the ultrastructural hallmarks of glomerular disease.

Silver enhancement of protein A-gold probes on resin-embedded ultrathin sections. An electron microscopic localization of mouse mammary tumor virus (MMTV) antigens

A simple method is described allowing the enhancement of the visibility of small gold probes for the electron microscopy. This method, which allows the silver intensification of gold directly on epon-embedded ultrathin sections, was used for the electron microscopic localization of Mouse Mammary Tumor Virus (MMTV) antigens in cultured cells derived from GR and BALB/cfRIII mouse mammary tumors. After the immunostaining with the preembedding protein A-gold technique, the ultrathin sections, placed on 200 mesh copper grids, were rehydrated and exposed to a photographic developer containing silver nitrate. During this physical development gold particles are incapsulated in growing shells of metallic silver, which gradually become more and more visible. We were able to obtain a heavy labelling of the viral particles, well visible even at low magnification, with a negligeable background staining. The present technique can be useful whenever it is necessary to use the smallest gold probes today available.

The morphogenesis of the human Paneth cell. An immunocytochemical ultrastructural study

In human duodenal mucosa Paneth cells originate away from the base of crypts and migrate towards the base during maturation. The earliest cells in the Paneth cell lineage could be identified by labelling of lysozyme in the Golgi apparatus. Specific labelling for lysozyme was present in the rough endoplasmic reticulum, Golgi apparatus, condensing vacuoles, granules and many lysosomes of mature Paneth cells. The maturation of the Paneth cell is accompanied by an increase in the content of lysozyme in the secretory granules and with senescence lysozyme diffuses into the cytoplasm.

Localization of atrial natriuretic factor (ANF)-immunoreactive material in the hypothalamo-pituitary complex of the frog

The presence of atrial natriuretic factor (ANF)-like material in the hypothalamo-pituitary complex of the frog (Rana ridibunda) was studied by means of indirect immunofluorescence and immunogold techniques. In the hypothalamus, numerous ANF-positive cell bodies were located in the preoptic nucleus, the lateral forebrain bundle and the dorsal infundibular nucleus. The ventral infundibular area and the median eminence contained only ANF-immunoreactive fibers. A dense network of fibers and nerve terminals was observed in the neural lobe of the pituitary. Scarce nerve endings were also noted in the intermediate lobe whereas ANF-like immunoreactivity was totally absent in the anterior lobe of the pituitary. At the ultrastructural level, positive material appeared restricted to dense core vesicles (about 100 nm in diameter). These results demonstrate that an ANF-like substance is contained in nerve terminals of the frog pars nervosa, and support the hypothesis that ANF may exert a physiological role in the control of release of neurohypophyseal peptides.

Preparation of protein colloidal gold complexes in the presence of commonly used buffers

In the presence of various commonly used buffers, phosphate-buffered saline (PBS), tris-buffered saline (TBS), Na-cacodylate, bovine serum albumin and a wide range of cytochemically active proteins (monoclonal and polyclonal IgG, concanavalin A, Ricinus communis lectin I, Helix pomatia lectin, protein A) were complexed to colloidal gold of different particle sizes (6 nm, 9 nm, 22 nm). The resulting complexes were active in cytochemical labelling. Complex-formation in the presence of electrolyte opens the possibilities of: maintenance of ionic environment during complexing of proteins sensitive to low ionic strength, pH control by addition of buffers to the protein solution or to the gold sol, direct coupling of protein supplied in PBS or saline avoiding dialysis against low ionic strength buffers. Using the electron microscope to estimate the protein amounts needed for stabilization provided a sensitive and economical method to obtain aggregate-free protein-gold complexes.

Endocytic traffic in trophectoderm and polarised blastomeres of the mouse preimplantation embryo

Endocytosis from apical and basolateral cell membranes of mouse blastocyst trophectoderm was examined morphologically by using unconjugated horseradish peroxidase (HRP, fluid phase marker), cationized ferritin (membrane marker, bound ionically), and protein A-HRP conjugate (membrane marker, identifying antigens recognised by antimouse species serum). The markers were applied in single and double labelling procedures designed to reveal the derivation, sorting site, and fate of all the major endocytic pathways. Endocytosis at the apical surface led to the obligate fusion of labelled elements with prelysosomal endosomes prior to the redistribution of membrane into lysosomal, transcellular, or recycling pathways, and to the passage of internalised fluid into lysosomes only. Complementary routes appear to operate following endocytosis at the basolateral domain. Thus, endocytic trafficking within the trophectoderm, regulated by "sorting" mechanisms localised at the endosome compartment, may be responsible for the maintenance of polarised membrane domains. The polarised transcellular pathway involving obligatory endosome fusion is present in cleavage-stage, peripheral 16-cell blastomeres prior to zonular tight junction formation. Nocodazole treatment to depolymerize microtubules in many cases induced a bypass of the endosomal sorting compartment during transcytosis, indicating that microtubules contribute to the spatial organization of endocytic membrane traffic.

Alkaline phosphatase conjugated protein A as a sensitive reagent to immunoscreen an expression cDNA plasmid library: isolation of cDNA to the calcium-binding protein of the chick embryonic chorioallantoic membrane

A highly efficient immunoscreening procedure has been developed to isolate cDNA clones to the calcium-binding protein (CaBP) of the chick embryonic chorioallantoic membrane (CAM). A library of total CAM cDNA was constructed using the expression plasmid vector, pUC 19. Bacterial clones containing plasmids with CaBP cDNA inserts were detected immunohistochemically based on their expression of hybrid CaBP protein sequences. For immunodetection, nitrocellulose bacterial colony replicas were treated with specific antibodies to the CaBP followed by incubation with Staphylococcus aureus Protein A conjugated with alkaline phosphatase (AP) which served as a secondary immunoreagent. Positive clones were then histochemically identified based on AP enzyme activity. The identity of the immunopositive clones was further verified by in vitro translation of mRNA selected by hybridization to the cloned cDNA. The AP-based immunoscreening procedure yields stable reaction products with relatively low background, and should find general application for isolating specific cDNA clones from expression cDNA libraries.

Rapid identification of proteins on flat surfaces, using antibody-coated metal oxide suspensions

Suspensions of Fe3O4 (black), Fe2O3 (red), and Cr2O3 (green) were exposed to solutions of protein A, and then each to a different antiserum to one of the following human proteins: fibrinogen, high molecular weight kininogen (HMK), albumin or immunoglobulins (IgG). Test surfaces were patterns of human proteins adsorbed out of solutions or out of plasma, onto glass as well as onto polyvinylchloride slides. They were exposed to single or mixed suspensions of the treated oxides for about 30 s and rinsed. Adhesion of each oxide onto each matching protein of these patterned test surfaces resulted, thus identifying each protein by color.

Demonstration of OKT6 antigen on human thymic dendritic cells in culture

In situ, two types of dendritic cells (DCs) have been characterized in more detail: the interdigitating DCs of peripheral lymphoid tissues and the epidermal Langerhans cells. In order to characterize human thymic DCs, normal human thymus specimens were obtained from children undergoing cardiovascular surgery. In culture, DCs could be easily differentiated from macrophages and epithelial cells by their long fine processes, irregular nucleus, and dark, membrane-bound granules. By immunoelectron microscopy, using the protein A-gold and the avidin-biotinperoxidase complex techniques, cultured DCs were strongly labeled with anti-Ia and anti-OKT6 monoclonal antibodies. These results demonstrate that the phenotype of thymic DCs is similar to that of epidermal Langerhans cells and suggest that they may belong to the same cellular lineage.

Choice of immunoglobulin G purification method in assays for antibodies to the thyrotropin receptor

Activity of autoantibodies to the thyrotropin receptor in the serum of patients with active Graves's disease was compared when the patients' IgG was purified by three different procedures: ammonium sulfate precipitation (I), a modified batch diethylaminoethyl cellulose method (II), and affinity chromatography on Protein A-Sepharose CL-4B (III). IgG extracted by I was significantly less potent in inhibiting binding of 125I-labeled thyroid membranes than that prepared by either II or III, and was significantly less effective than II in stimulating adenyl cyclase activity in thyroid membrane. Thyroglobulin, a serum protein whose concentration is increased in patients with various thyroid diseases, was coprecipitated in amounts sufficient to significantly inhibit binding only when method I was used, but not with either of the other two procedures. Evidently method I is inferior to either of the other two when used for purification of autoantibodies to the thyrotropin receptor. Method II used in this study, being faster and more economical than I and of equivalent efficacy, is a feasible alternative method for clinical use.

Enhancement of sensitivity of the haemagglutination test for echinococcosis by use of Staphylococcus aureus protein A

A modification of the indirect haemagglutination test is described for the serodiagnosis of echinococcosis. In the modified test the Cowan I strain of Staphylococcus aureus, which contains protein A, was used to enhance haemagglutination of sensitised red cells. The test was performed in parallel with the indirect haemagglutination test on 31 sera from surgically-confirmed cases of hydatid disease and on 45 sera from healthy blood donors. Use of S. aureus protein A enhanced the sensitivity of the test and greatly increased the titres obtained with most of the sera. None of the sera from healthy blood donors exhibited a titre greater than 64, whereas all but two of the sera from cases of hydatid disease exhibited titres greater than 128. The immunoassay is simple, inexpensive and requires little technical skill. It has the potential for wide application in the serodiagnosis of echinococcosis.

Cross-reactivity of birch anthers and leaves with birch pollen antigens and allergens. A fine-structural immunocytochemical study using the post-embedding protein-A-gold technique

Ultra-thin sections of vegetative tissues from birch (anthers and leaves) were labeled for pollen antigens and allergens using a commercial rabbit IgG antibody preparation directed against birch pollen antigens and allergens. Antibody binding sites were visualized using the protein A-gold technique. Specific labeling occurred in anther tissue (tape-tum cells, anther wall cells) as well as in the birch leaf (assimilation parenchyma). In both types of tissue, antigens and allergens were detected throughout the living protoplast (including cell organelles such as nuclei, mitochondria, and plastids). The cellulose cell walls were always free from anti-birch-pollen IgG-binding sites. The immunological controls (normal rabbit IgG) showed a low degree of nonspecific labeling. In plant tissues belonging to genera quite different from birch (tulip anther, rhododendron leaves), after incubation with the specific IgG weak labeling was observed. The immunological basis for these results is discussed.