Nitrocellulose-enzyme-linked immunosorbent assay (NC-ELISA) - a sensitive technique for the rapid visual detection of both viral antigens and antibodies

Development of a gold-nano particle based novel dot immunobinding assay for rapid and sensitive detection of Banana bunchy top virus

An improved gold nanoparticle based Dot immunobinding assay (DIBA) was developed for the detection of Banana bunchy top virus (BBTV), that is more efficient, sensitive, rapid and simpler than conventional DIBA and ELISA. Instead of enzyme conjugates, gold nanoparticles were used as reporters owing to their unique optical properties. Antibody was raised against expressed recombinant coat protein of BBTV. The gold nanoparticles were conjugated to primary / detection antibody raised following immunization with recombinant coat protein, making it highly specific for the virus. Gold nanoparticle conjugated primary antibody (GCPab) based DIBA developed in this study has a detection efficiency comparable to ELISA. The results of using this assay format for detection of BBTV in banana plants from four geographical regions of India are also presented in this report. The test could detect the virus at sap dilution up-to 10^-2. Using this improved DIBA, any lab with basic amenities can perform indexing on large numbers of samples.

Biofunctional paper via the covalent modification of cellulose

Paper-based analytical devices are the subject of growing interest for the development of low-cost point-of-care diagnostics, environmental monitoring technologies, and research tools for limited-resource settings. However, there are limited chemistries available for the conjugation of biomolecules to cellulose for use in biomedical applications. Herein, divinyl sulfone (DVS) chemistry was demonstrated to immobilize small molecules, proteins, and DNA covalently onto the hydroxyl groups of cellulose membranes through nucleophilic addition. Assays on modified cellulose using protein-carbohydrate and protein-glycoprotein interactions as well as oligonucleotide hybridization showed that the membrane's bioactivity was specific, dose-dependent, and stable over a long period of time. The use of an inkjet printer to form patterns of biomolecules on DVS-activated cellulose illustrates the adaptability of the DVS functionalization technique to pattern sophisticated designs, with potential applications in cellulose-based lateral flow devices.

Dot immunobinding assay method with chlorophyll removal for the detection of southern rice black-streaked dwarf virus

Southern rice black-streaked dwarf virus (SRBSDV), a new virus from Fiji, has seriously damaged rice crops in southern China and northern Vietnam in recent years. This virus is difficult to diagnose in the early stages of infection, and is very destructive at the late stage. In the present study, a dot immunobinding assay (DIBA) that has a high sensitivity for diagnosing SRBSDV was developed. Two kinds of treatment for the DIBA were evaluated to determine the most effective one for removing chlorophyll interferences via rice extraction. The first included several reagents to remove chlorophyll, namely, the alkaline reagents like magnesium oxide and alumina oxide, the adsorbent reagents like activated carbon and bentonite, as well as the extraction agent acetone. The second and third treatments, which were used to remove chlorophyll in blot membrane-nitrocellulose and polyvinylidene fluoride (PVDF), included several organic solvents containing methanol, ethanol, acetone, ethyl acetate, and diethyl ether. The results showed that activated carbon and methanol yielded the best contrasting purple color for the infected samples by decreasing the chlorophyll content.

Effects of smoking and treatment status on periodontal bacteria: evidence that smoking influences control of periodontal bacteria at the mucosal surface of the gingival crevice

BACKGROUND

We examined whether smoking status could influence growth of potentially pathogenic bacteria in the periodontal environment of treated and untreated periodontal patients.

METHODS

We have previously reported effects of treatment status on marker bacteria in our patients. We established a history of any smoking during 6 months prior to microbiological sampling (F-ME, 16 smokers out of 64; MHM, 70 smokers out of 185). We used a commercial immunoassay to quantitate Porphyromonas gingivalis, Prevotella intermedia, and Actinobacillus actinomycetemcomitans in paper point samples from periodontal sites.

RESULTS

Logistic regression showed that in smokers, neither P. gingivalis nor A. actinomycetemcomitans was quantitatively increased, while P intermedia was somewhat increased. Multiple regression demonstrated that smoking disrupts the positive relationship between increasing probing depth and increasing bacterial growth that is found in non-smokers. In smokers, growth of marker bacteria at shallow sites (< or =5 mm) was significantly increased to the levels found at deeper sites (>5 mm) in both smokers and non-smokers. Supragingival plaque biofilm was identified as a reservoir for marker bacteria; smokers and nonsmokers had equal ranges of oral cleanliness.

CONCLUSIONS

Smoking-associated periodontitis is not simply a reflection of oral cleanliness. Smoking extends a favorable habitat for bacteria such as P. gingivalis, P. intermedia, and A. actinomycetemcomitans to shallow sites (< or =5 mm). Molecular byproducts of smoking interfere with mechanisms that normally contain growth of damaging bacteria at the surface of the oral mucosa in gingival crevices. In this way, smoking can promote early development of periodontal lesions.

Performance of a commercial immunoassay for detection and differentiation of periodontal marker bacteria: analysis of immunochemical performance with clinical samples

BACKGROUND

We employed a commercial immunoassay for simultaneous detection and differentiation of marker bacteria Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, and Prevotella intermedia and reassessed the immunochemical performance of the assay.

METHODS

We compared the analytical performance of the immunoassay in our study of clinical samples from 249 periodontal patients in 2 private periodontal practices with the previously reported analytical performance of the same immunoassay. We also compared immunoassay measurements of the marker bacteria in clinical samples with values obtained in other studies by direct culture of the same organisms.

RESULTS

The assay produced 3 times more high-end readings than reported previously. We also reassessed and revised previously published calibration curves for the immunoassay. The immunoassay provided measurements of the marker bacteria in clinical samples from our patients that were comparable to and consistent with measurements of the same bacteria by direct culture in other studies.

CONCLUSIONS

We ascribe the increased sensitivity of the immunoassay in our study to: 1) a more standardized and vigorous sample dispersion that improves release of particulate and soluble antigens from dental plaque biofilm, and 2) better visualization of the reaction product of the enzyme-linked immunoassay. High-technology assays, such as diagnostic immunoassays, have a significant potential for future development in dental diagnosis, because they simplify detection and measurement of biologically important markers such as specific bacteria in clinical samples. Commercial assays also have an important potential for standardization of clinical measurements of biological markers.

The use of filter paper plasticized with polyvinyl alcohol-glutaraldehyde in ELISA

F1-antigen purified from Yersinia pestis was covalently linked to 5-mm diameter filter paper discs plasticized with polyvinyl alcohol-glutaraldehyde. These discs were used both for ELISA and dot-ELISA for the detection of anti-F1 IgG in rabbits. The best conditions were achieved using 1.25 microg of F1 antigen/disc, 3% w/v skim milk in PBS as blocking agent, anti-IgG peroxidase conjugate diluted 12,000 times, and serum from rabbits immunized or not against Y. pestis, diluted 6,400 times. The absorbance values obtained from the comparative study between this procedure and conventional ELISA were not significantly different but the low cost of the reagents employed in ELISA using the filter paper discs plasticized with polyvinyl alcohol-glutaraldehyde makes this method economically attractive.

A nylon membrane enzyme immunoassay for rapid diagnosis of influenza A infection

A new membrane-enzyme immunofiltration assay (MIFA) was developed for rapid diagnosis of influenza A infection. The pretreated specimens were dispensed into a 1.2 micron Biodyne B nylon membrane-bottomed microplate and vacuum filtration was applied. Blocking solution, peroxidase-conjugated anti-influenza A nucleoprotein monoclonal antibody, washing buffer and substrate were added in that order. The assay was completed within 30 min. Out of 103 nasopharyngeal swabs collected in transport medium, 31 isolates of influenza A virus were obtained and 22 specimens were detected directly by the MIFA technique. The 9 isolation-positive MIFA-negative specimens required 6 days or more for viral detection in cell culture, and probably contained a very low quantity of virus. The 72 cell culture negative specimens were also negative by MIFA. Comparison with a classical immunocapture assay (ICA) gave a better sensitivity for MIFA, as only 15/103 specimens were positive by ICA. MIFA is a rapid test with 71% sensitivity and 100% specificity. It was also very useful to test the cell culture supernatants, as a sensitivity of 100% was obtained with MIFA when the immunofluorescence technique was positive. The same technique could be readily carried out on the same plate for other respiratory viruses since capture antibody is not used.

Sensitive avidin-biotin amplified fluorogenic enzyme immunoassay using biotinylated monoclonal antibodies for the identification and quantitation of virus

A highly sensitive amplified fluorogenic enzyme-linked immunosorbent assay (FELISA), which utilizes the high affinity interaction of the vitamin biotin for the multiple binding sites on the glycoprotein avidin, was developed for the detection and identification of a model virus, Newcastle disease virus (NDV). Monoclonal antibodies (MCA) directed against the virus were purified and labelled with biotin. Biotinylated MCA was then used with avidin-labelled enzyme and a fluorogenic substrate to detect NDV adsorbed directly on nitrocellulose membranes. Reagents were standardized and, using purified virus, the theoretical lower limit of test sensitivity of the amplified FELISA was determined to be 1 fg/ml of test sample (50 ag/well). The specificity of the amplified FELISA was evaluated by challenging the assay system with homologous and heterologous strains of NDV, and with other serologically related and unrelated viruses. The test was simple to perform and multiple samples could be conveniently assayed with results obtainable in 3-4 h.

Nucleotide sequence of the 3' terminal region of lettuce mosaic potyvirus RNA shows a Gln/Val dipeptide at the cleavage site between the polymerase and the coat protein

DNA complementary to the 3' terminal 1651 nucleotides of the genome of the common strain of lettuce mosaic virus (LMV-O) has been cloned and sequenced. Microsequencing of the N-terminus enabled localization of the coat protein gene in this sequence. It showed also that the LMV coat protein coding region is at the 3' end of the genome, and that the coat protein is processed from a larger protein by cleavage at an unusual Q/V dipeptide between the polymerase and the coat protein. This is the first report of such a site for cleavage of a potyvirus polyprotein, where only Q/A, Q/S, and Q/G cleavage sites have been reported. The LMV coat protein gene encodes a 278 amino acid polypeptide with a calculated Mr of 31,171 and is flanked by a region which has a high degree of homology with the putative polymerase and a 3' untranslated region of 211 nucleotides in length. Percentage of homology with the coat protein of other potyviruses confirms that LMV is a distinct member of this group. Moreover, amino acid homologies noticed with the coat protein of potexvirus, bymovirus, and carlavirus elongated plant viruses suggest a functional significance for the conserved domains.

Detection and titration of measles virus antibody by hemagglutination inhibition and by dot immunobinding

Measles continues to be a major disease of both human and nonhuman primates. The dot immunobinding assay, a modified enzyme immunoassay, permits the detection of measles virus antibody in the nonlaboratory setting with either serum or whole blood collected on filter paper.

Enterohemolysin production is associated with a temperate bacteriophage in Escherichia coli serogroup O26 strains

A temperate bacteriophage that determines the expression of enterohemolysin was isolated from Escherichia coli O26 strain C3888. The genetic determinant associated with enterohemolysin production (E-Hly determinant) was cloned from EcoRI-digested bacteriophage DNA in vector plasmid pUC8. pUC8 recombinant plasmid pEO19 carries a 3.7-kb EcoRI insert of phage DNA, and enterohemolysin was expressed in E. coli K-12 after transformation. Hemolysin-negative derivatives of pEO19 were generated by transposon mutagenesis with Tn1725. By subcloning, the phage E-Hly determinant was assigned to a 2,150-bp piece of DNA which is flanked by EcoRI and AccI restriction sites. The enterohemolysin-producing recombinant strains and wild-type strain C3888 express a 60-kDa protein which was detected in the bacterial outer membrane by Western immunoblotting. Biologically active enterohemolysin was detected only in bacteria grown to the stationary phase, and the hemolysin was not released into the culture medium. Lysis of erythrocytes was inhibited by 30 mM dextran 4, which functions as an osmotic protectant without destroying the enterohemolysin itself.

Sandwich-dot immunobinding assay (Sandwich-DIA), a new immunological method for the detection of diphtheria toxin

In this paper we describe a new assay for diphtheria toxin in bacterial cultures, based on a sandwich-dot immunobinding method. This method uses horse polyclonal diphtheria antitoxin as the coating antibody and mouse monoclonal diphtheria antitoxin as the detecting antibody. The sensitivity of this new method is within a range of 5-10 ng toxin per ml in Corynebacterium diphtheriae cultures. We did not observe any false-positive reactions. As a solid phase we used nitrocellulose disks which bind protein more strongly than the commonly used plastic solid phase. Results with strong toxin producers of C. diphtheriae can be obtained as soon as 11 h after starting a bacterial test culture. To detect weak toxin producers, the cultivation period must be extended to about 18 h and the results can be obtained after about 24 h. The method presented in this paper is simpler, faster and more reliable than currently used methods.

A dot immunobinding assay on nitrocellulose for the detection of bovid herpesvirus-4 antibodies

A dot immunobinding assay (DIA) was developed for the detection of antibody against bovid herpesvirus-4 (BHV-4) in bovine sera. A semipurified virus preparation was used as the antigen and an antispecies horseradish peroxidase-labeled IgG and diaminobenzidine were employed as the detection system. The sensitivity and specificity of the DIA were similar to those of indirect fluorescent antibody test, indicating the suitability of DIA as a rapid field test for the detection of anti-BHV-4 antibodies in cattle.

A dot-ELISA for the detection of IgG antibodies to mumps and varicella viruses

An enzyme-linked immunosorbent assay using nitrocellulose strips (dot-ELISA) for the routine laboratory detection of IgG antibodies to mumps and varicella viruses is described. The virus antigens are dotted onto nitrocellulose strips, and the dotted strips are incubated with the sera to be tested. The bound antibodies are revealed using enzyme-labeled antihuman IgG antibodies. Reliable results are obtained when the assay is carried out at 37 degrees C. The reported data indicate that the dot-ELISA can reliably be used for the detection of IgG antibodies to mumps and varicella viruses in human sera.

A dot-ELISA intended for the specific and simultaneous detection of antibodies directed to antigens derived from Toxoplasma gondii, rubella virus, cytomegalovirus, and type 1 and type 2 herpesviruses

A procedure for the routine and simultaneous laboratory detection of IgG antibodies produced in humans in the course of various infectious diseases is described. The procedure, based on dot-enzyme-linked immunosorbent assay (ELISA), used single nitrocellulose strips onto which several antigens were dotted in close proximity. Optimal conditions were specified that allowed the unequivocal and simultaneous detection of IgG antibodies specifically directed against Toxoplasma gondii, rubella virus, cytomegalovirus, and herpes simplex virus type 1 and type 2 antigens. This technique has proved to be simultaneously specific, sensitive, and reliable, and it has been applied to prenatal screening of sera from pregnant women. It is suggested that this technique should also be used for the screening of large numbers of sera under field trial conditions.

An amplified dot immunoassay for the direct quantitation of adapted and wild strains of human cytomegalovirus

A rapid and simple quantitative dot immunoassay for a cell-adapted reference strain of cytomegalovirus (CMV) and for wild strains of CMV present in clinical urine samples was developed. The assay was performed on nitrocellulose paper dotted with several dilutions of viral pellets free of cellular debris. Viral dilutions were treated with a monoclonal antibody to the major component of the viral capsid. To amplify the reaction, a three-dimensional complex of streptavidin and biotinylated horseradish peroxidase was used as the detector system. The dot immunoassay, which does not require cell cultures, yielded results within one day. A significant correlation was found between CMV titers obtained by dot immunoassay and CMV infectious units determined by immunoalkaline phosphatase staining of CMV-late antigen positive cells.

The use of a nitrocellulose-enzyme immunoassay for the rapid screening of monoclonal antibodies to human enteroviruses

A simple, indirect enzyme immunoassay using purified enterovirus adsorbed on to nitrocellulose has been developed for screening monoclonal antibodies to enteroviruses. The sensitivity of the assay ranged from 10 ng to 1 microgram of viral protein and was 10- to 50-fold more sensitive than conventional EIA on microplates. This simple, sensitive and specific assay proved to be a useful and practical tool for detecting monoclonal antibodies which would not be found in a conventional EIA screening procedure.

Sensitive fluorogenic enzyme immunoassay on nitrocellulose membranes for quantitation of virus

A highly sensitive fluorogenic enzyme-linked immunosorbent assay (FELISA), which utilizes nitrocellulose membranes as solid phase support, has been developed for the detection and identification of virus in clinical samples. Reagents were standardized and, using purified Newcastle disease virus (NDV) as a model, the theoretical lower limits of test sensitivity of the FELISA were compared, in both "sandwich" and "indirect" formats, to those of a comparable chromogenic enzyme-linked immunosorbent assay (CELISA). Of the systems evaluated, the "sandwich" FELISA exhibited maximum sensitivity and detected 10 fg of purified virus protein per milliliter of test sample (500 ag per test volume). Specificity of the "sandwich" FELISA was evaluated by challenging the system with heterologous strains of NDV and with other serologically related and unrelated viruses. In a clinical trial in which fecal materials from chickens undergoing vaccination with NDV were assayed directly by FELISA, the virus was detected from the first to approximately the tenth day post-vaccination. The test is simple to perform and results can be obtained in approximately 4 h.

A quantitative nitrocellulose enzyme immunoassay and its application to the screening of hybridomas for the detection of uncharacterized tumor-associated antigens in sera of cancer patients

An enzyme-linked immunosorbent assay on nitrocellulose based microtiter plates for the detection of uncharacterized tumor associated antigens in squamous cell carcinoma and adenocarcinoma cancer patients' sera is described. Nitrocellulose microtiter plates are more sensitive than the plastic plates of polystyrene and polyvinyl chloride for the detection of antigens in serum. Monoclonal antibodies were selected for their net reactivities toward cancer patients' sera as compared to normal sera. Sera from benign liver and kidney disease patients and activated human peripheral blood leukocyte supernatant were used to reduce potential false positives toward inflammatory and benign diseases. Using this system, fourteen antibodies were selected out of over eight hundred antibodies for their potential serodiagnostic application.

A nitrocellulose membrane based solid phase enzyme immunoassay for detecting polioviruses in stool

An enzyme immunoassay was developed with nitrocellulose membrane as the solid phase support built in a 96 well porous polystyrene plate. Monoethanolamine was found to be a satisfactory and better blocking agent than skimmed milk. Up to 10(4.28) TCID50 poliovirus particles/0.1 ml of stool collected in 10% skimmed milk could be detected depending on the initial titer of the antigen specific capturing serum/IgG immobilized on nitrocellulose membrane. Percentage of skimmed milk in the transport medium, composition and pH of the dilution buffer and chloroform treatment of the stool specimens before the test were important determinants of the specificity of the test. Polyvinyl affinity membrane did not appear to be superior to nitrocellulose membrane as a solid phase support.

Blocking dot-ELISA, using a monoclonal antibody for detection of antibodies to bluetongue virus in bovine and ovine sera

A modified solid phase blocking enzyme immunosorbent assay (ELISA), using a monoclonal antibody (McAb) against the group specific bluetongue virus (BTV) antigen is described for detection of anti-BTV antibodies in cattle and sheep sera. Dots of an optimal dilution of BTV antigens were adsorbed to nitrocellulose (NC) paper (hence dot-ELISA) and then the remaining adsorptive sites were saturated with gelatin. After exposure to bovine or ovine test serum the NC strips were reacted with the McAb. The presence of McAb was detected with a peroxidase-conjugated anti-mouse IgG (H and L). In the absence of anti-BTV antibody in test sera, BTV antigen sites were reactive with McAb as indicated by a brown colored dot after enzyme degradation of hydrogen peroxide in the presence of diamino benzidine (DAB) or amino ethylcarbazole (AEC). In the presence of sufficient anti-BTV antibody no color reaction was observed. The blocking (B) dot-ELISA was superior to the agar gel immunodiffusion (AGID) in detecting anti-BTV antibodies in bovine and ovine sera early after experimental infection with BTV type 10. In 5 of 7 animals inoculated by combined intravenous and subcutaneous routes, anti-BTV antibodies in sera were detectable as early as 7 days post infection (DPI), all of which were AGID negative. Comparable B-dot-ELISA and AGID results were found in 23 paired sera (pre and 20 DPI) from cattle experimentally infected with different types of BTV and in 100 AGID negative sera from Ontario dairy and Alberta beef cattle.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitrocellulose dot-ELISA for serodiagnosis of schistosomiasis

The diagnostic value of the nitrocellulose (NC)-ELISA technique originally described for the detection of viral and bacterial antigens was studied for the detection of antibodies in patients with parasitologically confirmed schistosomiasis, using only about 100 ng total protein content per NC disc of Schistosoma mansoni soluble egg antigen supplied by WHO. The results showed excellent sensitivity: 100% (38/38) for S. mansoni cases and 93.6% (44/47) for S. haematobium. The specificity tested on 50 sera of persons from non-endemic areas was also 100%. 34 sera of patients suffering from other parasitoses were also included. 3 sera of 10 from filariasis cases reacted positively by NC-ELISA, but they were also positive by indirect immunofluorescence, indicating a possible undetected Schistosoma infection. One positive reaction among sera from 4 toxocariasis cases was not confirmed by further tests. We conclude that the NC-ELISA can be a useful technique, especially in developing countries where tests with low cost equipment are needed. Large-scale screening studies should be done to evaluate its usefulness under field conditions.

A combined dot nitrocellulose-enzyme immunoassay for rotavirus and adenovirus

A combined enzyme immunoassay using nitrocellulose membrane as solid support is described for the detection of rotavirus and adenovirus in faeces from children with gastroenteritis. Its sensitivity and specificity are comparable to those of a previously described assay performed on plastic microplates (Pereira et al. (1985) J. Virol. Methods 10, 21-28). The introduction of nitrocellulose membrane as support for the immune reactions greatly simplifies the multiple washing steps and precludes the need for disposable plastic plates.

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.

Self-contained enzymic membrane immunoassay for detection of rotavirus antigen in clinical samples

A self-contained enzymic membrane immunoassay (SCEMIA) system has been developed for the detection of viral antigens in clinical samples. The assay system makes use of antiviral antibodies bound to a nylon membrane, a flow-through washing procedure, and a clearly visible endpoint of the enzymic reaction. A SCEMIA system with antibodies against rotavirus detected rotavirus antigen, within 15 min, in all faecal samples from children with gastroenteritis that were positive for antigen in a standard microplate enzyme immunoassay, which took 4 h to complete. In addition, the SCEMIA could detect rotavirus in faecal samples collected from infected individuals both before and after antigen could be detected by a standard immunoassay system. Rotavirus antigen was not detectable in control children who did not have evidence of rotavirus infection. SCEMIA systems are an accurate, rapid, and inexpensive means for the practical diagnosis of viral infections in human beings.

Single antibody dot immunoassay--a simple technique for rapid detection of a plant virus

A single antibody dot immunoassay (SADI) was developed for use as a rapid, simple and sensitive technique for the direct assay of virus bound to nitrocellulose membranes. SADI has been tested for the detection of subterranean clover mottle virus (SCMoV) in small amounts of infected tissue and purified virus preparations, and the technique was found to be twelve times more sensitive than ELISA in terms of total antigen detected. DIBA, an indirect dot immunoassay, was about twice as sensitive as SADI, but the latter was more specific for the detection of SCMoV and is a simpler, more rapid assay, requiring less than three h to complete.

Dot-enzyme immunoassay for visual detection of antibodies to pseudorabies virus in swine serum

A modified solid-phase enzyme immunoassay (EIA) is described for the visual detection of anti-pseudorabies virus (anti-PRV) antibody in porcine serum. Dots of PRV antigens were adsorbed to nitrocellulose paper (hence the name dot-EIA), and the remaining nonspecifically reactive sites were blocked with bovine serum albumin or skim milk powder. After immersion in test serum, bound antibodies were reacted with a peroxidase-conjugated anti-porcine immunoglobulin G (H & L). Positive reactions were easily visualized as brown dots after enzyme degradation of a substrate containing hydrogen peroxide and diaminobenzidine. The dot-EIA was comparable to the serum neutralization test and the standard microtiter EIA in its ability to detect antibody in the sera of pigs 9 days after experimental infection and 12 days after contact with infected pigs. The sensitivity and specificity of the dot-EIA relative to the serum neutralization test and the standard EIA were determined from the testing of 856 field sera from the United Kingdom, the United States, and Canada. In all comparisons, both the relative sensitivity and specificity of the dot-EIA were in the order of 98 to 99%. The dot EIA appears to have potential application as a rapid and economical field test in the diagnosis of PRV infection.

Rapid dot-immunobinding assay on nitrocellulose for viral antibodies

A procedure is described for the routine laboratory diagnosis of viral serum antibodies. Antigens are dotted on nitrocellulose strips or sheets, and sera are applied on absorbent paper strips. Antigen-antibody complexes are detected with enzyme-conjugated antiglobulin and development of a colored, insoluble substrate product. The test allows processing of multiple sera in one 3- to 5-h operation and is equal to or more sensitive than serum neutralization, hemagglutination inhibition, and fluorescent antibody assays. Highly infectious viruses inactivated with a psoralen derivative and long-wavelength UV light irradiation can be used as antigens, allowing the study of human pathogens. Although the test detects cross-reacting, group-specific herpesvirus antigens, the intensity of the antibody reaction is greatest with type-specific antigens. Preliminary data suggest that the technique will be useful for the rapid typing of viruses from clinical specimens.

Enzyme-linked immunoassays for the detection of microbial antigens and their antibodies

Antibodies could be labeled with enzymes for use in histochemical staining procedures by enzyme-immunoassay (EIA). The use of EIA is an extension of previously used serological tests, using enzyme-labeled antibody or antigen to determine antibody content. Direct detection of antigen by EIA represents a more dramatic departure from previous methods based on culture. Also, the method has enabled detection of infectious agents that are difficult to cultivate, such as hepatitis A virus and rotavirus, or agents that cannot be cultivated, such as hepatitis B. The use of EIA tests for detection of microbial antigens provides an alternative to culture as a means for direct identification of a specific microbial agent. It also provides a means to detect microbial agents which have not been successfully propagated. The detection of circulating antigen or detection of antigen in other body fluids by EIA is more difficult than detection of antibody because of the sensitivity required, and because of interfering substances in specimens such as feces and respiratory secretions. For this reason, very few antigen detection assays have the sensitivity and specificity required to be used as a primary diagnostic test. The number of tests that have been developed, however, is impressive and because of the possibilities for rapid, specific diagnosis, the interest in antigen detection by EIA remains high.

Use of the nitrocellulose-enzyme immunosorbent assay for rapid, sensitive and quantitative detection of human enteroviruses

A modified enzyme immunosorbent assay (EIA) employing nitrocellulose (NC) membrane as a high-capacity solid phase was successfully employed for the sensitive and rapid detection of human enteric viruses, poliovirus and Coxsackievirus B-5. The sensitivity of the NC-EIA ranged from 7 to 70 pg of viral antigen diluted in phosphate-buffered saline. When virus was added to crude supernatants of mollusc tissue homogenates prepared by the standard procedure for the recovery of viruses in molluscs, the sensitivity was reduced by approximately 10-fold. The sensitivity of the NC-EIA for the detection of viral antigens was 10- to 100-fold higher than conventional EIA using polystyrene microtiter plates as solid phase supports. This simple, rapid and sensitive assay using minimal amounts of antibodies should prove to be a useful and practical diagnostic tool to augment infectivity assays currently employed by various virus monitoring procedures. The method also may be applicable for the detection of difficult to grow and/or non-cultivatable enteric viruses which may be present in sewage-contaminated environments.

In situ enzyme immunodetection of surface or intracellular bacterial antigens using nitrocellulose sheets

We describe an immunological method which allows the in situ colorimetric detection of translated DNA fragments in bacteria. In the absence of lysis only cell surface proteins are detected. For cytoplasmic proteins, lysis is required. The procedure comprises the following steps: bacteria are lysed, the proteins are transferred onto a disc of nitrocellulose sheet, the remaining protein sites are blocked, the disc is successively soaked in a solution of antibodies specific for the protein to be detected and in a solution of peroxidase-labelled anti-IgG antibody solution. Finally, the immune complexes are made visible by enzyme substrate incubation. We describe the application of this method to the detection of the LamB protein, the LacZ protein, and a LamB-polio VP1 chimera translated from cloned DNA fragment in E. coli.

Detection of picogram quantities of potyviruses using a dot blot immunobinding assay

Highly sensitive direct visual detection of potyviruses was achieved using a dot blot immunobinding assay (DBIA). The small sample volumes required permit the detection of as little as 0.5 pg virus in purified preparations. The binding of rabbit antibodies could be visualized using goat anti-rabbit IgG (GAR) conjugated to alkaline phosphatase, beta-D-galactosidase, glucose oxidase, or horseradish peroxidase and histochemical substrates. The avidin-biotin system was also useful, but somewhat less sensitive than GAR-enzyme conjugates. Detection of potyviruses in an aphid vector was also attempted, but without success due to endogenous aphid enzymes.