Development of a sensitive protein A-gold immunoelectron microscopy method for detecting viral antigens in fluid specimens

Immunoelectron Microscopy of Viral Antigens

Immunoelectron microscopy is a powerful technique for identifying viral antigens and determining their structural localization and organization within vaccines and viruses. While traditional negative staining transmission electron microscopy provides structural information, identity of components within a sample may be confounding. Immunoelectron microscopy allows for identification and visualization of antigens and their relative positions within a particulate sample. This allows for simple qualitative analysis of samples including whole virus, viral components, and viral‐like particles. This article describes methods for immunogold labeling of viral antigens in a liquid suspension, with examples of immunogold‐labeled influenza virus glycoproteins, and also discusses the important considerations for sample preparation and determination of morphologies. Together, these methods allow for understanding the antigenic makeup of viral particulate samples, which have important implications for molecular virology and vaccine development. © 2019 The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Immunohistochemical Detection of Porcine Rotavirus Using Immunogold Silver Staining (IGSS)

Immunogold silver staining (IGSS) was applied for the detection of porcine group A rotavirus in formalin-fixed paraffin-embedded tissue sections of small intestine. Prior to the application of IGSS, the reactivity of protein A-gold as a marker was tested with group-specific antiserum in immunogold electron microscopy. Immune aggregates were intensely and specifically labeled with the gold complex. Application of IGSS to tissue sections resulted in specific dark staining of villous enterocytes infected by group A rotavirus. This method also proved effective for the detection of rotaviral antigen in infected cultured cells. The IGSS method may be suitable for routine diagnostic detection of rotaviral infections and may have application for detection of other viral pathogens of veterinary importance.

The use of convalescent sera in immune-electron microscopy to detect non-suspected/new viral agents

Negative staining electron microscopy methods can be employed for the diagnosis of viral particles in animal samples. In fact, negative staining electron microscopy methods are used to identify viruses, especially in minor species and wild animals, when no other methods are available and in cases of rare, emerging or re-emerging infections. In particular, immune-electron-microscopy with convalescent sera is employed to detect etiological agents when there are undiagnosed clinical outbreaks, when alternative diagnostic methods fail due to the lack of immunological reagents and primers, and when there is no indicative clinical suspect. An overview of immune-electron-microscopy with convalescent sera’s use in the diagnosis of new and unsuspected viruses in animals of domestic and wild species is provided through the descriptions of the following four diagnostic veterinary cases: (I) enteric viruses of pigs: Porcine Rotavirus, Porcine Epidemic Diarrhea Virus, Porcine Circovirus and Porcine Torovirus; (II) Rotavirus and astrovirus in young turkeys with enteritis; (III) Parvovirus-like particles in pheasants; and (IV) Lagoviruses: Rabbit Hemorrhagic Disease Virus and European Brown Hare Syndrome Virus.

Immunocytochemical characterization of viruses and antigenic macromolecules in viral vaccines

Gold immunolabeling combined with negative staining (GINS) provides a valuable immunocytochemical approach that allows a direct ultrastructural definition of all viral vaccine constituents that share common antigenic features with pathogenic viral particles. These results have implications for the development of viral vaccines since it has been demonstrated that incomplete viral particles such as natural empty capsides and Rotavirus-like particles lacking the infective genome are potential candidates for the production of neutralizing antibodies. Furthermore comparative results of the application of GINS to either inactivated vaccines or unfixed samples provide direct evidence that even after inactivation specific antigenic sites are still available for gold immunolabeling.

Redirected infection of directly biotinylated recombinant adenovirus vectors through cell surface receptors and antigens

The inability of adenovirus to infect primitive hematopoietic cells presents an obstacle to the use of adenovirus vectors for gene transfer to these cell types. Therefore, expanding the tropism of adenovirus vectors to unique cell surface antigens would be an important development for gene therapy protocols. In this study, we sought to redirect infection of adenovirus vectors to primitive human hematopoietic cells that universally express the c-Kit receptor on their cell surface. To accomplish this, a vector was constructed by covalently linking biotin molecules to recombinant adenovirus, followed by addition of the biotinylated ligand for the c-Kit receptor, stem cell factor (SCF), through an avidin bridge. Gene transfer was directed specifically to c-Kit-positive hematopoietic cell lines, resulting in up to a 2,440-fold increase in luciferase expression with frequencies equivalent to recombinant virus infection of permissive cells. Substitution of biotinylated antibodies directed against c-Kit, CD34 (binds L-selectin), and CD44 (hyaluronate receptor) receptors for biotinylated SCF resulted in 50-, 8-, and 260-fold increases in reporter gene expression, respectively, demonstrating that infection also could be redirected through antibody-antigen interactions and through antigens other than growth factor receptors. The versatility of this vector was demonstrated further by infection of primary T cells with vectors targeted with antibodies to CD44 (resting and activated T cells) and biotinylated IL-2 (activated T cells only). Taken together, directly biotinylated adenovirus vectors represent a versatile and efficient method for redirection of virus infection to specific cells.

Serotyping of human astrovirus strains by immunogold staining electron microscopy

Human astrovirus strains were propagated in CaCo-2 cell cultures, and virus multiplication was demonstrated by immunosorbent electron microscopy (ISEM). Serotyping of the virus strains was carried out in cell culture fluids or directly in faecal extracts by an indirect immunogold staining (IGS) electron microscopy technique, using specific rabbit antisera against astrovirus types 1-6 as primary antibodies and goat anti-rabbit IgG gold conjugate as secondary antibody. Thirty-seven astrovirus strains were examined, of which 26 grew in the cell cultures in several passages. IGS of the cell-derived viruses showed that 16, 3, 3, and 4 of the strains were types 1, 2, 3, and 4 respectively. Types 5 and 6 were not demonstrated. Eleven strains did not grow in cell cultures, and attempts to serotype these strains by IGS directly in the faecal extracts were unsuccessful, except for one strain which was found to be type 1. The results indicate that IGS may be a specific and suitable method for serotyping astroviruses grown in cell cultures.

Immunodominant antigens of zoospores from ovine isolates of Dermatophilus congolensis

Zoospores of Dermatophilus congolensis were analysed by SDS-PAGE and western blotting. The electrophoretic profiles of zoospores from 13 isolates of D. congolensis were similar but not identical when stained with Coomassie blue or silver. Immunodominant polypeptides with apparent molecular masses of 76 and 31 kDa were identified in western blots of 13 of 13 and 12 of 13 isolates respectively of D. congolensis reacted with hyperimmune, ovine, antizoospore sera. Identical immunodominant polypeptides were observed in western blots reacted with sera obtained from naturally infected sheep. Initial characterisation of the 76 and 31 kDa polypeptides indicated that they were probably surface exposed because (i) antibodies eluted from the surface of live zoospores after adsorption of hyperimmune antizoospore serum, reacted principally against the 76 and 31 kDa subunit polypeptides in western blots, (ii) adsorption of hyperimmune antizoospore serum with live zoospores resulted in significant diminution of reactivity against both the 76 and 31 kDa polypeptides in western blots, (iii) indirect fluorescent immunostaining of zoospores with antiserum prepared against gel-purified 76 kDa polypeptide, resulted in intense staining of the zoospore outer coat. Immuno-gold electron microscopy of negatively stained zoospores with antiserum prepared against gel-purified 31 kDa polypeptide identified this antigen as a flagella subunit.

Colloidal gold labeling of sections and cell surfaces

Colloidal gold labeling techniques can be simplified enough to become practical for diagnostic use in a hospital electron microscopy laboratory. Methods found to be practical and reproducible are presented, including production of colloidal gold reagents, polar embedding for gold labeling of thin sections, and use of silver enhancement on semithin sections. Methods for cell surface labeling are emphasized; they are technically straightforward and can be applied to investigation of multiple diagnostic problems.

Etiology of rabbit haemorrhagic disease spontaneously occurring in Korea

Causative agent of rabbit haemorrhagic disease (RHD) was purified by CsCl density gradient centrifugation from the liver homogenate of rabbits infected with RHD virus which originated from Korea. The viral particles were 35-40 nm in diameter, and had hollow depressions on their surface. Protein A-gold immunoelectron microscopy clearly showed that the convalescent antisera of diseased rabbits reacted specifically with the virus particles. SDS-PAGE and Western blot analyses demonstrated that the structural protein of the virus was composed of a single major polypeptide of 63 kD. These findings indicate that the causative agent of RHD, tentatively named as picornavirus in Korea, belongs to calicivirus.

Detection of Norwalk-like virus and specific antibody by immune-electron microscopy with colloidal gold immune complexes

Direct electron-microscopy (DEM), immune electron microscopy (IEM) and four different procedures of immune electron microscopy with colloidal gold immune complexes were evaluated for the detection of Norwalk-like virus and specific antibody. A solid-phase immune electron microscopy with colloidal gold immune complexes-triple layer method (SPIEMGIC-TLM) is developed for screening patients' specimens for the detection of Norwalk-like virus and its specific antibody. The method demonstrates low non-specific background labelling and is simple, sensitive and easy to perform. A quadruple layer method (SPIEMGIC-QLM), which is a modification of the triple layer method, has been established by adding a cross-linking anti-IgG layer to amplify the reaction and to provide a more sensitive test which is suitable for screening monoclonal antibodies prepared against 32-34-nm Norwalk-like virus isolated in our laboratory.

Identification of coronaviruses by the use of indirect protein A-gold immunoelectron microscopy

Concentration by airfuge and protein A-colloidal gold immunoelectron microscopy (PAG-IEM) offered a rapid and sensitive method for detection and identification of coronaviruses from various species. The method was applied to partially purified tissue culture-adapted or egg-adapted mammalian and avian coronaviruses and to clarified fecal samples from diarrheic calves and turkey poults for detection of enteric coronaviruses. Aggregates of virus coated with specific antibody were seen in virus samples mixed with homologous antiserum but not in control samples containing preexposure serum. At least a 10-50-fold enhancement of the sensitivity of direct EM for virus detection was obtained using protein A-colloidal gold complex as an electron-dense marker. The PAG-IEM method demonstrated low nonspecific background labeling and permitted detection of soluble and particle-associated antigen. Reciprocal cross-reactivity was detected among the subgroup of mammalian hemagglutinating coronaviruses, and antisera to 4 members of other subgroups only recognized their homologous virus.

Rapid identification of Ebola virus and related filoviruses in fluid specimens using indirect immunoelectron microscopy

Recent filoviral outbreaks in animal primates have raised public awareness of the potential for filoviruses to become a public health concern; methods that efficiently identify these viruses are therefore of high priority. An indirect immunoelectron microscopy method, which uses homologous guinea pig polyclonal antiserum, successfully identified Ebola-related (Reston) virus particles in serum and tissue culture fluid specimens with infectivity titres of 300 plaque forming units (pfu) per ml or more. The sensitivity of this procedure is sufficient to show virus in most acute phase sera, and is equal to that of the antigen capture enzyme linked immunosorbent assay (ELISA). The immunoelectron microscopy fluid technique can differentiate among antigenically distinct filoviruses in less than three hours. It should be valuable in the rapid diagnosis of potential filoviral infections.

The development of protein A-gold electron microscopy for immunological studies of Haemophilus somnus

Two separate experiments were conducted using modifications of protein A-gold immunoelectron microscopy (PAGIEM) to evaluate the ability of sera from calves vaccinated against Haemophilus somnus to bind virulent organisms (experiment I) and to detect differences in the antibody accessible antigenic sites on the outer membrane of selected strains of H. somnus having different virulence attributes using a high IgG2 titre specific bovine hyperimmune serum (experiment II). The results of experiment I demonstrated that the direct opsonisation of H. somnus by specific antisera was related to its IgG2 titre. In experiment II, strain-dependent differences in the labelling of antigenic sites by specific IgG2 antibodies were observed. The virulent strains of both septicaemic and genital isolates of H. somnus showed higher protein A-gold labelling than their non-virulent counterparts. The results from a comparison of pathogenic and non-pathogenic respiratory isolates did not reveal the same difference in labelling intensity. The studies demonstrated the PAGIEM technique to be a sensitive, versatile and a reliable laboratory method to analyse antigen-antibody interactions of H. somnus.

Negative staining in the detection of viruses in clinical specimens

Viruses have unique morphology and are therefore good candidates for negative staining. Negative staining with phosphotungstic acid (PTA) or uranyl acetate has facilitated the detection of many viruses in clinical specimens. Enhancement procedures have included the use of centrifugation and agar diffusion for concentrating virus particles, the use of solid phase capture reagents to trap virus particles and the use of secondary antibodies and electron dense markers to help visualize them. Techniques currently in use and employing negative staining include direct EM, immune electron microscopy (IEM), solid phase immune electron microscopy (SPIEM), colloidal gold-labeled protein A (PAG), solid phase IEM employing a second decorator antibody (SPIEMDAT), and solid phase IEM using colloided gold-labeled secondary antibodies (SPEIMDAGT). IEM methods assist with the detection of small viruses or viruses present in low numbers while PAG offers increased sensitivity over direct EM and IEM. In our experience the serum-in-agar (SIA) method is the most sensitive of the PAG IEM techniques for detection of rotavirus particles in clinical specimens. SPIEMDAT enhances the detection of small viruses which are often missed by other techniques due to background staining in specimens. SPEIMDAGT employing colloidal gold-labeled secondary antibody has increased sensitivity and offers the advantage of detecting viral antigen when whole virus particles are not visible. IEM techniques have recently been used for typing viruses using either monospecific antisera or monoclonal antibodies and colloidal gold-labeled secondary antibody.

A new immune complex dot assay for detection of rotavirus antigen in faeces

A new immune complex dot assay (ICDA) using immune gold/silver staining is described for the sensitive and rapid detection of rotavirus in cell culture and stool specimens. The method involves spotting preformed antigen-antibody complexes onto nitrocellulose paper, followed by incubation with colloidal gold-labelled secondary antibody and silver enhancement. ICDA was sensitive and specific and detected rotavirus antigens over a wide range of concentrations. It was more sensitive than a conventional immunodot assay (CIDA) and two commercial enzyme immunoassays (EIA) based on testing serial dilutions of a positive stool specimen. Of 26 stool specimens tested ICDA detected rotavirus antigen in 17; 14 were positive by Pathfinder Rotavirus EIA, 16 by Testpack Rotavirus EIA, and direct electron microscopy (DEM) detected only 12. The ICDA offers improved sensitivity over commercial EIAs and DEM.

Sensitive solid-phase immune electron microscopy double-antibody technique with gold-immunoglobulin G complexes for detecting rotavirus in cell culture and feces

A new solid-phase immune electron microscopy double-antibody colloidal-gold technique (SPIEMDAGT) was developed and compared with direct electron microscopy, direct immune electron microscopy, and enzyme immunoassay for detecting rotavirus. Guinea pig and rabbit antirotavirus antisera were used as capture and detector antibodies, respectively, and goat anti-rabbit immunoglobulin G-gold complexes were employed as a label. Animal rotavirus in cell culture media and human virus in stool specimens were detected by this method. On average, SPIEMDAGT detected 800 times more virus particles than direct electron microscopy and 45 times more particles than direct immune electron microscopy and yielded 20% more positives than enzyme immunoassay. SPIEMDAGT could detect not only viral antigen associated with morphologically recognizable particles but also antigen present when whole virus particles were not visible.

A 165 kd protein of the herpes simplex virion shares a common epitope with the regulatory protein, ICP4

We have investigated the possibility that immediate-early (IE) protein ICP4 could be a part of herpes simplex virus type 1 (HSV-1) virion particle. Immunodetection with a monoclonal antibody against ICP4 reveals that a component of the virion, migrating at 165 kd, shares a common epitope with this immediate-early protein. Immunolocalization studies on purified virions indicate that the antigen can be detected only in virions without membranes, and is located outside the capsid, most probably in the tegument. Ultrastructural localizations on HSV-1 infected BHK cells extracted with a nonionic detergent confirm that the protein immunoreacting with anti-ICP4 is present in virions.

Comparison of three protein A-gold immune electron microscopy methods for detecting rotaviruses

Three immune electron microscopic (IEM) methods employing protein A-colloidal gold (PAG) were compared with direct electron microscopy (DEM) and direct IEM (DIEM) techniques for their abilities to detect simian rotavirus (SA11) and human rotavirus. Using PAG IEM the number of rotavirus particles per grid square was 10 to 50 times and 2 to 5 times higher than observed with DEM and DIEM, respectively. A comparison of sensitivities among the three PAG IEM methods showed that the trapping efficiency for SA11 and human rotavirus was significantly enhanced by a serum-in-agar (SIA) method. The SIA method appeared to be a more reliable and sensitive alternative for detection and quantitation of viral particles.

Development of protein A-gold immunoelectron microscopy for detection of bovine coronavirus in calves: comparison with ELISA and direct immunofluorescence of nasal epithelial cells

A protein A-colloidal gold immunoelectron microscopy (PAG-IEM) technique was developed for the detection of bovine coronavirus (BCV) in the feces and nasal secretions of infected calves. Feces or nasal swab fluids were incubated sequentially with hyperimmune bovine anti-bovine coronavirus serum and protein A-gold, negatively stained, applied to formvar-coated copper grids and viewed using an electron microscope. The PAG-IEM method specifically identified BCV particles and possible subviral particles in feces and nasal-swab fluids from infected calves. The PAG-IEM method did not label other enveloped enteric viruses or morphologically similar fringed particles commonly found in feces. Detection of BCV using PAG-IEM was compared with ELISA and direct immunofluorescence (IF) of nasal epithelial cells by monitoring fecal and respiratory tract shedding of BCV from two experimentally infected and two naturally infected calves from birth to 3 weeks of age. PAG-IEM and ELISA detected shedding of BCV in fecal (4/4 animals) and nasal (3/4 animals) samples for an average of 5.25 days each. The observed agreement of BCV detection by PAG-IEM and ELISA was 85%. PAG-IEM may be a more sensitive immunoassay for the detection of BCV in diagnostic specimens from infected neonatal calves than ELISA. BCV infection of nasal epithelial cells was detected by immunofluorescence in 4/4 calves, persisted for the duration of the study in 2/4 calves and was sporadic in the other two animals. The observed agreement of BCV detection by PAG-IEM and IF was 57%.

Role of the virology laboratory in diagnosis and management of patients with central nervous system disease

A number of viruses cause acute central nervous system disease. The two major clinical presentations are aseptic meningitis and the less common meningoencephalitis. Clinical virology laboratories are now more widely available than a decade ago; they can be operated on a modest scale and can be tailored to the needs of the patients they serve. Most laboratories can provide diagnostic information on diseases caused by enteroviruses, herpesviruses, and human immunodeficiency virus. Antiviral therapy for herpes simplex virus is now available. By providing a rapid diagnostic test or isolation of the virus or both, the virology laboratory plays a direct role in guiding antiviral therapy for patients with herpes simplex encephalitis. Although there is no specific drug available for enteroviruses, attention needs to be paid to these viruses since they are the most common cause of nonbacterial meningitis and the most common pathogens causing hospitalization for suspected sepsis in young infants in the United States during the warm months of the year. When the virology laboratory maximizes the speed of viral detection or isolation, it can make a significant impact on management of these patients. Early viral diagnosis benefits patients with enteroviral meningitis, most of whom are hospitalized and treated for bacterial sepsis or meningitis or both; these patients have the advantage of early withdrawal of antibiotics and intravenous therapy, early hospital discharge, and avoidance of the risks and costs of unnecessary tests and treatment. Enteroviral infection in young infants also is a risk factor for possible long-term sequelae. For compromised patients, the diagnostic information helps in selecting specific immunoglobulin therapy. Good communication between the physician and the laboratory will result in the most benefit to patients with central nervous system viral infection.

The use of colloidal gold immunoelectron microscopy to diagnose varicella-zoster virus (VZV) infections by rapid discrimination between VZV, HSV-1 and HSV-2

Colloidal gold immunoelectron microscopy was used to diagnose rapidly 53 cases clinically suspected of varicella-zoster virus (VZV) infection and one special case selected from another study on typical herpes simplex virus (HSV) infections. The viruses were identified and subsequently typed within 2.5 h by a direct labelling test for VZV, and within 3.5 h by an indirect labelling test with monoclonal antibodies against HSV type 1 and type 2. The protein A purified IgG fraction of human anti-VZV immunoglobulins was adsorbed to colloidal gold particles, and the specificity of the gold-labelled antibodies was tested with several human and animal herpesviruses. Viral envelopes did not crossreact in the direct labelling test. However, an indirect labelling procedure revealed that a small fraction of the anti-VZV antibodies crossreacted with the cores of herpes simplex virus and pseudorabies virus (Aujeszky disease virus). Virus-infected cellular material taken from typical herpetic lesions was used directly without virus propagation for virus typing. All cases (N = 54) were analyzed without knowing the clinical description of the results of cytopathologic examination (Tzanck smear) and viral culture. Forty-four cases were identified as VZV; however, 5 of the supposed VZV infections were proved to be HSV infections. Although the viral culture of the one HSV case was HSV- and VZV-negative, colloidal gold labelling identified the case as VZV infection. In 16 cases virus immunoglobulin complexes were detected by using gold-tagged antibodies against human immunoglobulins. Immunoglobulins on the viral envelopes did not interfere with virus typing by immunogold labelling.

Electron microscopic method for determining the concentration of influenza virus antihemagglutinin antibodies of the IgG class

A novel technique for the determination of the concentration of influenza virus antihemagglutinin antibody of the IgG class is described which is based on the following principle: graded doses of purified antibody are allowed to react with homologous virus, resulting in binding of a portion of antibody. The virus-bound antibody is electron microscopically counted after labeling with protein A-gold. Since Freundlich's lambda-formula is valid for describing the relationship between antibody bound per virus particle and the corresponding concentration of unbound antibody, the values of bound antibody recorded can be used for calculating the concentration of unbound antibody. The antibody concentration of the test sample is obtained as sum of bound and unbound antibody. The antibody concentrations measured by use of this technique agreed well with chemically determined values.

Rapid virus subunit visualization by direct sedimentation of samples on electron microscope grids

Airfuge direct ultracentrifugation of viral samples on electron microscope grids offers a rapid way for concentrating viral particles or subunits to facilitate their detection and study. Using the A-100 fixed angle rotor (30 degrees) with a K factor of 19 at maximum speed (95,000 rpm), samples up to 240 microliters can be prepared for electron microscopy observation in a few minutes: observation time is decreased and structural details are highlighted. Using latex spheres to calculate the increase in sensitivity compared to the inverted drop procedure, we obtained a 10- to 40-fold increase in sensitivity depending on the size of particles. Application of this technique to rubella virus permitted better visualization of viral membrane subunits on the particles. Rubella hemagglutinin immuno-stimulating complexes preparations were also better visualized and their morphology conserved after direct ultracentrifugation on the specimen grids. Similar observations are reported for respiratory syncytial virus associated subunits.

Demonstration of calicivirus in human faeces by immunosorbent and immunogold-labelling electron microscopy methods

Immunosorbent electron microscopy (ISEM) and immuno-gold staining (IGS) electron microscopy methods have been applied to human faeces, shown by direct electron microscopy (EM) to contain calicivirus. Caliciviruses were successfully trapped on grids coated with positive rabbit or human antisera against calicivirus, but not with negative sera. Caliciviruses were specifically labelled with gold particles, when treated with positive rabbit or human antisera against calicivirus followed by protein A-gold and goat anti-rabbit or anti-human IgG gold conjugates in an indirect method in suspension. Goat anti-human IgM gold complexes did not react with the available antisera. Attempts to label caliciviruses trapped on the grids were unsuccessful. No cross-reactions were observed with Norwalk agent-like particles, hepatitis A virus or poliovirus type 3 by any of the methods. The results indicate that ISEM and IGS may be useful techniques for detection and identification of small viruses present in low concentrations in faeces.

Enumeration of enterovirus particles by scanning electron microscopy

Enumeration of virus particles requires relatively concentrated and uniformly dispersed virus preparations, which is difficult to achieve by the usual methods of negative staining and transmission electron microscopy. We have developed an electrophoretic method that concentrates enteroviruses onto a polycarbonate membrane for examination by high-resolution scanning electron microscopy. The electrophoretic apparatus comprises three chambers in electrical series, each containing 3.5 ml of dilute buffer. The center chamber is inoculated with virus. A 15-nm porosity membrane, which does not pass virus, separates the center from the side chambers. A constant current is applied, and chilled buffer is pumped past the electrodes for 2 h. The virus suspension is recovered, and changes in titer (or radioactivity if labeled virus is used) due to electrophoresis are measured. Buffer pH, relative to the viral isoelectric points, determines the direction of virus migration. Particle counts are calculated from the mean of 25 randomly chosen fields photographed at 35-60,000 X magnification and related to titers measured by plaque assay.

Use of gold IgG complexes and human antisera for electron microscopic identification of hepatitis A virus and polioviruses

An indirect immunogold staining technique was used for identification of hepatitis A virus and poliovirus types 1,2 and 3 by electron microscopy. Human convalescent antisera against hepatitis A virus and the three poliovirus types were used as primary antibodies and goat anti-human IgG gold complexes, with an approximate gold granule size of 15 nm, as secondary antibody. Hepatitis A virus was specifically labelled with the homologous antiserum. No labelling was observed when antiserum against poliovirus or other negative control sera were used as primary antibody. Poliovirus types 1, 2 and 3 were specifically labelled with a human serum with high titres of antibody against all three virus types. The use of type-specific antisera made it possible to distinguish types 1, 2 and 3 from each other, although slight cross-reactions occurred. The results indicate that gold IgG complexes in conjunction with human antisera may be used for identification of small spherical viruses.

Immunonegative stain techniques for electron microscopic detection of viruses in human faeces

Immune electron microscopy techniques have for some years been applied to detection of viruses in clinical specimens, especially faecal samples, as both sensitivity and specificity are improved by use of specific antibody. The following review describes in detail different preparation methods and illustrates some of the results that may be obtained.