New enzyme immunoassays for measurement of influenza A/Victoria/3/75 virus in nasal washes

Production and diagnostic application of monoclonal antibodies against influenza virus H5

Nine monoclonal antibodies (mAbs) against avian influenza virus (AI) H5 subtype from mice immunized with inactivated virus H5N1 (A/Turkey/ON/6213/66) were produced. Upon testing, the results indicated that the binding epitopes of eight out of the nine mAbs were conformational, while one mAb (#7) reacted with denatured H5N1 only. Two mAbs #10 and #11 reacted with all of the thirteen H5 strains tested indicating that the binding epitopes of these mAbs were conserved among these H5 subtypes. Possible applications of these mAbs in rapid tests for H5 antigen were explored. Double antibody sandwich (DAS) ELISAs were developed using two selected mAbs #10 and #11. This DAS ELISA detects specific H5 viruses and is able to identify all thirteen H5 strains tested. Three mAbs showed reactivity with AI H5 antigen for both immunofluorescence (IF) and immunohistochemistry. A cELISA used to screen chickens that had been infected with an H5 virus was developed with mAb #9 and recombinant H5 antigen. The sera from chickens that have been infected with an H5N1 virus were examined using the cELISA. 80% of the sera from H5 infected chickens showed a positive H5 specific antibody response at 7 days post-infection (dpi) and remained positive until the end of the experiment on day 30 (>40% inhibition). This panel of the AI H5 specific mAbs is valuable for the development of various immunoassays.

Development and Evaluation of a DAS-ELISA for Rapid Detection of Avian Influenza Viruses

Rapid detection of avian influenza virus (AIV) infection is critical for control of avian influenza (AI) and for reducing the risk of pandemic human influenza. A double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) was developed for this purpose. The method employed a monoclonal antibody (MAb) as the capture antibody and rabbit polyclonal IgG labeled with horseradish peroxidase as the detector antibody, and both antibodies were against type-specific influenza A nucleoprotein (NP). The DAS-ELISA could detect minimally 2.5 ng of influenza viral protein in virus preparations treated with Triton X-100, which is equvilent to 2.5 x 10(2) EID50 virus particles. This DAS-ELISA could detect all 15n AIV subtypes (H1-H15) and did not cross react with other avian pathogens tested. The DAS-ELISA were directly compared with virus isolation (VI) in embryonated chicken eggs, the current standard of influenza virus detection, for 805 chicken samples. The DAS-ELISA results correlated with VI results for 98.6% of these samples, indicating a sensitivity of 97.4% and specificity of 100%. The method was further tested with H5N1 and H9N2 AIV experimentally infected chickens, ducks, and pigeons, as well as field samples obtained from central China in 2005. The DAS-ELISA method has demonstrated application potential as an AIV screening tool and as a supplement for virus isolation in Asia.

Monoclonal antibodies for the rapid diagnosis of influenza-B virus infections by ELISA: production and characterization

BACKGROUND

Monoclonal antibodies directed against conserved epitopes of viral proteins have substantially improved the accuracy of several immunochemical methods in diagnostic virology.

OBJECTIVES

To characterize mouse monoclonal antibodies directed against structural protein antigens of influenza-B virus and evaluate their use as diagnostic reagents for the direct detection of such antigens in clinical specimens from patients with respiratory infections of unknown aetiology.

STUDY DESIGN

(a) Production and characterization of monoclonal antibodies against influenza-B viral antigens, and (b) their use in two different ELISA systems for detecting influenza-B antigen either directly in clinical specimens or after confirmation by rapid culture in MDCK cells.

RESULTS

Four monoclonal antibodies were selected for their specificity for the nucleoprotein antigen as demonstrated by Western blot analysis. The specificity of these antibodies for different epitopes of the nucleoprotein was demonstrated by competition experiments, using unlabelled and biotin-labelled purified antibodies in a sandwich assay. All four antibodies belong to the mouse IgG(2a) isotype, lack haemagglutination inhibition and neutralization properties and exhibit titres as high as 10(-6) in ELISA with as little as 30 ng purified influenza-B virus. ELISA methods using these antibodies detected only influenza-B viral antigens in direct testing of clinical specimens from patients with known influenza-B or influenza-A infections, or after reisolating virus from such specimens in tissue culture of MDCK cells.

CONCLUSION

The antibodies were suitable for the direct detection and typing of influenza-B virus in clinical specimens or for use in rapid confirmation cultures.

Tumor necrosis factor alpha exerts powerful anti-influenza virus effects in lung epithelial cells

Previous studies have associated influenza virus-induced expression of inflammatory cytokines, including tumor necrosis factor alpha (TNF-alpha), with influenza pathogenesis in the human respiratory tract and have suggested that alpha and beta interferons are the first cytokines recruited to counteract such infection. However, we report here that TNF-alpha has powerful anti-influenza virus activity. When infected with influenza virus, cultured porcine lung epithelial cells expressed TNF-alpha in a dose-dependent manner. Expression of TNF-alpha was induced only by replicating virus. TNF-alpha showed strong antiviral activity against avian, swine, and human influenza viruses, and the antiviral effect of TNF-alpha was greater than that of gamma or alpha interferon. These findings suggest that TNF-alpha serves as the first line of defense against influenza virus infection in the natural host.

A sensitive one-step immunocapture EIA for rapid diagnosis of influenza A

A highly sensitive one-step immunocapture EIA for the detection of influenza A virus antigen directly in a clinical specimen was developed. The sensitivity was achieved by using two high-affinity cross-reactive influenza type A-specific monoclonal antibodies, recognizing independent nonoverlapping epitopes on the influenza A nucleoprotein. One of the two MAbs was used as a capture antibody, while the other was coupled with enzyme peroxidase and served as a detector. Sensitivity to detection of highly purified recombinant influenza A virus nucleoprotein by EIA reached approximately 10 pg. Fifteen purified human influenza A virus strains of H1, H2 and H3 subtypes, isolated during the period 1934-1992, were tested by this system. All the influenza A viruses tested positive, whereas two influenza B viruses used as a control were negative. The efficiency of the system for detection of influenza A viral antigen directly in clinical specimens was confirmed by testing nasal and nasopharyngeal washes and aspirates, tested previously by time-resolved fluoroimmunoassay and by virus culture confirmation assay.

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.

Comparison of Directigen FLU-A with viral isolation and direct immunofluorescence for the rapid detection and identification of influenza A virus

Directigen FLU-A, an enzyme immunoassay membrane test, was compared prospectively to isolation in cell culture and direct immunofluorescence (IF) for the detection of influenza A virus. One hundred ninety specimens were evaluated by Directigen FLU-A and cell culture; 184 of these specimens were also tested by direct IF. The sensitivity of Directigen FLU-A compared to isolation in cell culture and direct IF was 100%. The specificities of Directigen FLU-A compared to isolation and direct IF were identical, 91.6%. Fourteen specimens that were positive by Directigen FLU-A did not yield virus in culture; two of the specimens, however, were positive by direct IF, and four other specimens were not specimens of choice for the test. A positive Directigen result had positive predictive values of 62.6 and 75.0% compared to isolation and direct IF, respectively; a positive Directigen result with an intensity reading of 2+ or greater, however, had positive predictive values of 85 and 100% compared to isolation and direct IF, respectively. In all comparisons, the negative predictive value was 100%. There was no evidence that cross-reactivity occurred with non-influenza A antigens. Directigen FLU-A should serve as a convenient screening test for influenza A and as a rapid test supported by isolation in cell culture during an influenza outbreak.

Comparison of enzyme-linked immunosorbent assay, indirect immunofluorescence assay, and virus isolation for detection of respiratory viruses in nasopharyngeal secretions

Nasopharyngeal secretions obtained from 94 children with acute respiratory illness were examined for the presence of respiratory syncytial virus (RSV), adenovirus, and influenza virus type A by virus culturing (virus isolation technique [VIT]), immunofluorescence assay (IFA), and enzyme-linked immunosorbent assay (ELISA). Similar results were obtained in at least two tests for RSV, influenza virus type A, and adenovirus in 92 (97.9%), 88 (93.6%), and 88 (93.6%) cases, respectively. Both rapid virus detection methods showed good specificity for the diagnosis of these virus infections (greater than or equal to 90.7%) and were more sensitive than was VIT for RSV detection. In a more accurate statistical analysis, the indexes of agreement between VIT and ELISA were substantial for RSV (kappa = 0.69; zeta = 5.5; P less than 0.0001), influenza virus type A (kappa = 0.67; zeta = 5.3; P less than 0.0001), and adenovirus (kappa = 0.71; zeta = 6.0; P less than 0.0001), while it was almost perfect for RSV when ELISA was compared with IFA (kappa = 0.88; zeta = 5.7; P less than 0.0001). Although the observed agreement was good in the comparison of these two tests for these three viruses (89%0, the indexes of agreement were moderate in the comparison of IFA and VIT for RSV (K = 0.55; Z = 2.0; P < 0.05), influenza virus type A (K = 0.42; Z = 9.7; P < 0.0001), and adenovirus (K = 0.41; Z = 6.5; P < 0.0001) and of ELISA and IFA for influenza virus type A (K = 0.55; Z = 7.0; P < 0.0001) and adenovirus (K = 0.59; Z = 6.8; P < 0.0001). All of the statistical evaluations demonstrated better agreement between ELISA and VIT for influenza virus type A and adenovirus.

Detection of influenza viruses in throat swab by using polymerase chain reaction

An assay protocol based on exploiting the polymerase chain reaction (PCR) for the direct detection of influenza virus in throat swab is described. By use of the mixture of H1 and H3 primers, it was possible to determine the subtype of the influenza A viruses simultaneously. No visible band was detected after PCR of influenza B or A (H2N2) viruses with a pair of H1 or H3 primers. The dilution experiment showed that the influenza viruses, as few as 1.3-6 plaque-forming units, were sufficient for detecting the HA gene by PCR. All throat swab samples from which influenza viruses had been isolated by conventional method were also positively detected by PCR method.

Evaluation of a new enzyme-linked immunosorbent assay (ELISA) in the diagnosis of rhinovirus infection

This study describes the evaluation of a newly developed ELISA for the direct detection of rhinovirus antigens in nasal washings. Of 54 volunteers inoculated with 100 TCID50 of human rhinovirus type 2 (HRV-2), 50 (96.6%) and 32 (59%) excreted antigen and virus on at least 1 of 3 days investigated, respectively. Thirty-three (61%) had significant rises in rhinovirus-specific IgA by ELISA. Twelve (22%) developed symptoms of colds. Generally the ELISA detected antigen more frequently in volunteers later in the course of infection and provided evidence of infection in a higher proportion of asymptomatic compared with symptomatic volunteers. On the other hand, virus isolation detected virus more frequently earlier in the course of infection and in a higher proportion of symptomatic compared with asymptomatic volunteers. We conclude that rhinovirus antigen detection by ELISA is a simple, rapid, sensitive, and practical test to diagnose a rhinovirus infection and potentially a viable alternative to virus isolation.

Enzyme-linked immunosorbent assay of core antigens for clinical diagnosis of influenza

A solid-phase enzyme-linked immunosorbent assay (ELISA) with monoclonal secondary antibodies was used to detect matrix protein and nucleoprotein of influenza A. The sensitivity of the ELISA for highly purified A/Brazil nucleoprotein and matrix protein was 0.05 and 1.0 ng, respectively. Nasal washes from 10 of 20 adult subjects with culture-proven, naturally acquired infection caused by A/Brazil/11/78-like influenza virus were positive in the test, and 2 of 13 subjects with rhinovirus infection were falsely positive. To determine if ELISA results could be improved, nasal washes were obtained from 21 adult volunteers who had been inoculated intranasally with wild-type A/Korea/1/82 (five subjects) or A/Korea recombinants with matrix protein or RNA-2 protein of A/Ann Arbor/6/60 (16 subjects), and the nasal washes were processed by a variety of methods. Prompt addition of sodium azide to the nasal washes to limit bacterial growth, avoidance of freezing, and the use of an antiproteolytic agent all failed to improve ELISA results noticeably. Under the best conditions, ELISA was positive in only 12 of the 21 experimentally infected subjects and in 1 of 15 uninfected controls. Positive ELISA results in experimentally infected subjects correlated significantly with the titer of live virus in the nasal washes (r = +0.506; P less than 0.001). Detection of gradient-purified whole influenza virus or isolated core antigen in ELISA was inhibited by prior incubation with nasal washes, and the inhibitory activity was only partly decreased by heat treatment of the secretions. At present, the use of ELISA for detection of influenza antigens in respiratory secretions is not sufficiently sensitive or specific for routine laboratory diagnosis of influenza.

Rapid etiological diagnosis of pneumonia in young men

The major findings and conclusions of the present study are: 1. Evidence of the etiology of the pneumonia was established in 86% of 106 young men with pneumonia. Pneumococcus was the most common etiologic agent; it was detected definitely in 30% of the pneumonia patients, and possibly in another 20%, by blood culture, sputum culture, antigen detection, and serological methods. 2. Pneumococcal antigen detection from purulent pretreatment sputum samples was the best rapid diagnostic method for pneumococcus; it was capable of identifying 90% of the pneumococcal pneumonias definite by our criteria, whereas sputum Gram stain was positive in 65% of these. 3. Detection of adenoviral antigens from nasopharyngeal specimens (NPS) by EIA or IF method or adenovirus DNA by HYB method showed good specificity but a somewhat lower sensitivity than did adenovirus isolation from NPS. 4. Adenovirus antigens and DNA can be demonstrated also from sputum specimens. 5. EIA is slightly superior to the CF method in detecting antibody responses to adenovirus, but the detection of different antibody classes offers no additional diagnostic possibilities. 6. Isolation of Mycoplasma pneumoniae from bronchoalveolar fluid in pneumonia patients is a specific and sensitive method in the diagnosis of mycoplasmal pneumonia. 7. It seems possible to differentiate by clinical signs and symptoms and by high CRP (over 85mg/1) and WBC (over 10 x 10(9)/1) values pneumococcal pneumonias from viral, mycoplasmal and mixed pneumonias and from upper respiratory infections. Moderately elevated CRP values were observed in adenoviral (Mean 50 mg/1) and in mycoplasma (mean 59 mg/l) pneumonias, as well as in MRI (mean 44 mg/l).

Detection of influenza viruses through selective adsorption and detection of the M-protein antigen

A model system has been developed which permits rapid detection of influenza viruses through targeting of the M (membrane or matrix)-protein; a type-specific antigen, in an enzyme-linked immunosorbent assay system. This technique exploits the hydrophobic properties of M-protein; the M-protein is selectively and rapidly adsorbed to polystyrene surfaces even in the presence of a 5000-fold excess of bovine serum albumin. Hyperimmune antiserum prepared to purified M-protein is used as the detecting reagent. All type A influenza viruses could be detected by this technique, type B influenza viruses reacted to a slight extent and Sendai virus (parainfluenza virus, type 1) did not react. Virus could be detected to levels as low as 3 ng. Purification of M-protein and preparation of hyperimmune sera from other related virus groups, such as type B influenza viruses, paramyxoviruses and rhabdoviruses should permit detection of these agents by a similar technique.

Time-resolved fluoroimmunoassay with monoclonal antibodies for rapid diagnosis of influenza infections

Monoclonal antibodies that are broadly reactive with either influenza A or influenza B viruses were used to develop a 2- to 3-h antigen capture time-resolved fluoroimmunoassay (TR FIA) for detecting influenza viral antigens in both original nasopharyngeal aspirate specimens and in tissue cultures inoculated with nose or throat swab specimens. The lower limit of sensitivity of the assay was about 10 pg of protein as determined with purified influenza A nucleoprotein expressed by recombinant DNA. When the TR FIA was performed with 96 nasopharyngeal aspirate specimens collected during outbreaks of influenza A (H3N2) virus and the results were compared with serodiagnosis results with paired sera, the specificity and sensitivity of TR FIA for the demonstration of influenza A infections were 95 and 85%, respectively. In culture confirmation assays, more than 80% of the swab specimens that grew influenza A or B virus within 7 days could be identified by the TR FIA within 48 h of the inoculation of cells. The results are consistent with those previously reported for respiratory syncytial virus and extend the applicability of monoclonal antibody-based TR FIA for the rapid diagnosis of acute respiratory viral infections.

Rapid diagnosis of respiratory adenovirus infections in young adult men

Rapid viral diagnosis was attempted in 106 military conscripts with pneumonia and in 101 military conscripts with other types of respiratory infections. Nasopharyngeal suction specimens (NPS) were assayed for viral antigens by immunofluorescence and enzyme immunoassay (EIA). Sputum specimens from 97 pneumonia patients were assayed for viral antigens by EIA. Also, 71 NPS and 13 sputum specimens were examined for the presence of adenovirus DNA by a sandwich hybridization (HYB) method. The reference test was adenovirus isolation in cell culture from the NPS. Adenoviruses were isolated from 6 pneumonia patients and from 20 patients with other respiratory infections. Of these 26 NPS, rapid diagnosis was successful in 13, 16, and 14 cases by EIA, immunofluorescence, and HYB, respectively. Four antigen-positive specimens were found among the 181 specimens which were negative by virus isolation. Sputum was found to contain adenovirus antigen by EIA in 5 of 97 tested specimens. Of these 97 specimens, 13 were selectively tested in HYB, and a positive signal was observed in 4 cases. Serological testing of paired sera revealed 23 adenovirus infections in the pneumonia group and 42 in the group with other respiratory infections. Other viral infections were found only sporadically. All rapid virus detection methods showed excellent specificity but had a lower sensitivity (60%) than virus isolation. Our results show that rapid methods for diagnosing respiratory adenovirus infections can be successfully used in selected groups of adults.

Detection of respiratory syncytial virus in nasopharyngeal secretions by enzyme-linked immunosorbent assay, indirect immunofluorescence, and virus isolation: a comparative study

An enzyme-linked immunosorbent assay (ELISA) was developed for the detection of respiratory syncytial virus (RSV) antigens in nasopharyngeal secretions (NPS) from children with acute respiratory disease. Antisera against RSV nucleocapsids were used as immunoreagents for this test system. The results obtained by RSV antigen ELISA were compared to those of indirect immunofluorescence (IF) and tissue culture virus isolation (TC). Of the 404 NPS obtained, 278 were tested in parallel by ELISA and IF and 205 by ELISA and TC, and 89 were screened in parallel by all three methods. The sensitivity of ELISA in relation to IF was 86.7%, the specificity 95.7%. Sensitivity and specificity obtained by ELISA were 89.9% and 94.4%, respectively, compared to TC. False-negative results were obtained with all three test systems used.

Rapid diagnosis of respiratory virus infections in patients with acute respiratory disease

Viral respiratory infections represent a significant segment of the total respiratory disease spectrum; however, until recently the laboratory diagnosis of viral respiratory infections was relatively inefficient. Development of new and improved immunologic assay systems has paved the way for accurate and reliable rapid diagnostic tests that detect viral antigens in clinical specimens. We conducted a careful and elaborate study in which radioimmunoassay for antigen detection was compared with a battery of tissue culture systems for viral isolation and identification. Using a fine plastic catheter, a specimen of mucus was aspirated from the nasopharynx of patients with clinical signs and symptoms of acute viral upper respiratory tract infections. Each specimen was divided into two portions; one was used to inoculate a variety of tissue culture cell lines and the other was used for radioimmunoassay tests for influenza A and B, adenovirus, parainfluenza 1, 2, and 3, and respiratory syncytial virus. Radioimmunoassay results compared very favorably with the tissue culture data with only one exception--adenovirus. Essentially this degree of accuracy and reproducibility was obtained with an enzyme-linked immunosorbent assay test, which has replaced radioimmunoassay. Tissue cultures are still used for backup, but with a rapid antigen detection system in place, coupled with a modern computer program to facilitate the laboratory data to the clinician, considerable strides have been made, and will continue to be made, in the diagnosis and therapy of viral respiratory tract infections.

Characterization and evaluation of monoclonal antibodies developed for typing influenza A and influenza B viruses

Monoclonal antibodies that are broadly reactive with influenza A or influenza B viruses were produced as stable reagents for typing influenza viruses. Monoclonal antibodies to influenza A were specific for either matrix protein or nucleoprotein. The antibodies to influenza B were specific for nucleoprotein or hemagglutinin protein. In an enzyme immunoassay procedure, influenza A antibodies detected H1N1, H2N2, and H3N2 influenza A virus strains collected between 1934 and 1984. Each of the influenza B antibodies detected influenza B reference viruses collected between 1940 and 1984. Pools of either influenza A or influenza B monoclonal antibodies were used to detect influenza viruses reisolated from clinical specimens in tissue culture. At 48 h after inoculation, the influenza A monoclonal antibodies detected 64% of H1N1 and 94% of H3N2 influenza A specimens, and the influenza B monoclonal antibodies detected 79% of the influenza B specimens. The results of this study suggest that the monoclonal antibodies described should provide useful diagnostic reagents for workers in virology laboratories who wish to isolate and identify influenza virus but have been unable to obtain consistent supplies of animal sera specific for influenza A or B viruses.

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.

Which of the commonly used marker enzymes gives the best results in colorimetric and fluorimetric enzyme immunoassays: horseradish peroxidase, alkaline phosphatase or beta-galactosidase?

Comparing the marker enzymes horseradish peroxidase (HRP), alkaline phosphatase (AP) and beta-galactosidase (beta Gal) in IgG-coupled form with respect to their temperature-dependent kinetics over a period of 22 h the temperature of 37 degrees C warrants highest substrate turnover for all enzymes at all reaction times using fluorogens. Also applying chromogens the optimum temperature for beta Gal is 37 degrees C and depends for HRP and AP on the reaction time. The substrate turnover of HRP using ABTS as chromogen is much higher compared to the other enzymes--both related to mol enzyme (molar activity) and to gram enzyme (specific activity). The turnover decreases for all enzymes in different degrees after coupling to IgG. The turnover of fluorogenic substrates is lower for all enzymes than the turnover of chromogenic substrates but due to the more sensitive detection of fluorogenic products the detection limits for all conjugates were lowered too--especially for beta Gal-IgG by a factor of 333 compared to the colorimetric procedure. In a 2-site binding enzyme immunoassay for alpha-1-fetoprotein (AFP) the detection limit for AFP was reduced by a factor of 2 only by the fluorimetry compared to the colorimetry with all 3 marker enzymes. The HRP-IgG conjugates warranted lowest detection limits for AFP (0.5-1 microgram/1), highest analytical sensitivity (slope of standard curves) at shortest periods of substrate reaction compared to the other enzymes.

Stool desorbing activity: a possible cause of false-positive reactions in competitive enzyme immunoassays

We have developed a competitive enzyme immunoassay for the measurement of purified toxin A of Clostridium difficile. However, when we applied this assay to the detection of C. difficile toxin in stool specimens, we noted a high rate of nonspecific activity in fecal specimens which did not contain toxin. We found that the low specificity (26%) of the assay was due to the presence in stool specimens of interfering factors which desorbed the antigen coated on the solid-phase surface. These factors could be detected by measurement of the desorption of biotin-labeled proteins attached to the solid-phase surface. In addition, these interfering factors were partially inactivated by heating at 56 degrees C for 10 min and partially inhibited by phenylmethylsulfonyl fluoride (2 mM) or soybean trypsin inhibitor (10 mg/ml). These data suggested that the desorbing activity was due to proteolytic activity in the fecal specimens. Fetal calf serum (50%) was found to be the most effective measure in preventing the interfering effect. By using 50% fetal calf serum as a diluent, we increased the specificity of the antibody inhibition enzyme immunoassay to 93%. Interfering factors in stool specimens could be a cause of false-positive results in other competitive immunoassay systems. The use of diluents which neutralize protease activity can result in a marked improvement in the specificity of competitive immunoassay systems.

Enzyme immunoassay for the detection of group A streptococcal antigen

A competitive inhibition enzyme immunoassay for the detection of Streptococcus pyogenes directly from throat specimens or from solid bacteriological medium is described. Group A-specific polysaccharide adsorbed onto treated polystyrene beads, in conjunction with rabbit antibody to S. pyogenes, was used to determine the presence of the polysaccharide antigen. Inhibition values in excess of 65% were observed with 10(4) or more CFU of S. pyogenes per test. An inhibition of 25% was demonstrated with as few as 10(3) CFU per test. Heterologous microorganisms tested at 10(6) CFU per test reacted at levels of inhibition less than 25%. Two types of bacterial transport medium and swabs of different fiber compositions did not alter the assay performance. Accurate identification of S. pyogenes was achieved by testing single colonies picked directly from blood agar plates which had been incubated for 18 to 24 h. In addition, the assay was performed on throat specimens from children and adults having pharyngitis. A single-swab, blind study was conducted in which enzyme immunoassay reactivity was compared with results of blood agar culture and bacitracin sensitivity. When there were discordant results, serological identification was used as the confirmatory test. At an optimal cutoff value of 40% inhibition, sensitivity and specificity by enzyme immunoassay were 97.0% and 97.9%, respectively, as compared with confirmed culture results. The assay has an incubation time of 3 h and is a sensitive and specific method for the detection of S. pyogenes antigen.

Detection of respiratory virus antigens in nasopharyngeal secretions from patients with acute respiratory disease by radio-immunoassay and tissue culture isolation

An investigation was made of the sensitivity and specificity of four-layer radio-immunoassays (RIA) in the detection of adenovirus, respiratory syncytial virus, influenza virus types A and B, as well as para-influenza virus types 1, 2 and 3 from nasopharyngeal aspirates of 146 patients with acute respiratory disease. The sensitivity of RIA was comparable with that of tissue culture isolation if the total number of positives is considered. The difference may have been caused both by a higher efficiency of the RIA for detection of inactivated or non-cultivable agents and by a higher efficiency of tissue culture methods if the samples contained only small amounts of antigen. Differences between the two antigen detection systems were found in particular with respiratory syncytial virus and influenza B virus. At present, the use of tissue culture isolation together with RIA is the optimal routine laboratory procedure for the diagnosis of respiratory infections.

Etiological diagnosis of influenza A virus by enzymatic radioimmunoassay

An enzymatic radioimmunoassay for influenza A virus was developed by using polystyrene beads coated with rabbit immunoglobulin G to capture viral hemagglutinins (H1 and H3). Captured hemagglutinin was detected with goat immunoglobulin G followed by affinity-purified rabbit anti-goat immunoglobulin G labeled with alkaline phosphatase. [3H]AMP was added to quantify alkaline phosphatase activity, and free [3H]adenosine was measured with a scintillation counter. The assay detected as little as 0.1 ng of purified hemagglutinin. It was specific for hemagglutinin subtype and, depending on the source of the goat immunoglobulin G used, detected either H1 or H3. There was no reaction with neuraminidase or core antigens of influenza strain WSN-33. The clinical efficacy of the assay was evaluated with sequential nasal washes from 33 patients with naturally acquired H1N1 influenza. In the first 3 days of infection, the assay was consistently less sensitive than the viral culture, although detectable antigen persisted in secretions longer than did the infectious virus. Testing of multiple samples greatly increased the number of individuals in whom an etiological diagnosis could be made by immunoassay (81% of patients were positive for viral antigens at some point in their illness), and such testing was necessary to achieve the sensitivity of a single culture. Mean antigen levels were highest in nasal washes with the highest titers of infectious virus.

Serogrouping and subtyping of Legionella pneumophila with monoclonal antibodies

Monoclonal antibodies directed against Legionella pneumophila serogroups 1 to 6 were produced by fusing splenocytes of BALB/c mice with the Sp 2/0-Ag14 or the NSO mouse myeloma cell lines. Specificity of these antibodies was determined by indirect fluorescent-antibody staining: 8 reacted with L. pneumophila serogroup 1 and, respectively, 13, 6, 6, 5, and 10 reacted with serogroups 2, 3, 4, 5, and 6; all except 5 were serogroup specific, and none presented cross-reactions with six other species of Legionellaceae. Serogroup determination of 35 isolates of L. pneumophila with seven selected monoclonal antibodies resulted in correct serogrouping in all instances; a pool of the same seven monoclonal antibodies stained intensely all strains of L. pneumophila without any staining of the other species of Legionellaceae. When 24 serogroup 1 isolates of L. pneumophila were stained with eight serogroup 1-specific monoclonal antibodies, the staining patterns could be clustered in five distinct groups. These hybridomas thus represent an unlimited source of standard reagent that could be used in the detection and serogrouping of L. pneumophila; differences in staining patterns could be used as epidemiological markers for these bacteria.

Rapid viral diagnosis

There has been much interest and activity in the development of techniques for rapid viral diagnosis which would allow successful intervention in the treatment of patients or their contacts or in the control of viral diseases in the community. The greatest emphasis has been on techniques that permit viral detection directly in the clinical specimen, since these avoid the need to cultivate the agent, are feasible for detection of viruses that cannot be cultivated, and can detect virus in specimens in which the agent is no longer infectious. Direct methods used for viral detection include electron microscopy and various immunoassays which are based on demonstrating reactivity of viral antigen in the specimen with known viral antisera. The use of immunoassays for more rapid identification of viruses isolated in laboratory host systems and for selective detection of viral antigen in inoculated cell cultures even before the agents produce an observable effect has been an important advance in viral diagnosis by the approach of isolation and identification. The reliability of all specific viral identification procedures depends on the use of high quality viral antisera. Some of the problems previously encountered in preparing satisfactory viral immune reagents are being overcome through the availability of highly specific monoclonal antibodies produced by cell hybridization techniques. Virus-specific IgM antibody assays for rapid diagnosis have been improved greatly through the use of a "capture" technique in which antibody to the human mu chain is used in the solid phase to separate IgM from other serum components which might compete with IgM antibody or give nonspecific reactivity, and also through the availability of highly specific monoclonal antibodies to the human mu chain. A variety of simple assays for determination of viral antibody status have been developed, and many are commercially available. The reliability of some of these antibody assays has been improved through the incorporation of more suitable controls and through better definition of interpretations which should be made from test results.

Sensitive enzyme immunoassay with beta-D-galactosidase-Fab conjugate for detection of type A influenza virus antigen in clinical specimens

The most sensitive method for diagnosis of type A influenza virus infection is isolation of the agent in cell culture. However, detection and identification may require several days to complete. This delay in diagnosis prevents effective use of the antiviral agents available for treatment of type A influenza infection. As a rapid diagnostic method, enzyme immunoassay (EIA) is attaining increased usage for direct detection of viral antigen in clinical specimens. Standard EIA techniques, however, are usually not sensitive enough for reliable detection of viral antigen in respiratory secretions. We developed a conjugate consisting of the antigen-binding fragment of goat antirabbit immunoglobulin G coupled to beta-d-galactosidase, using the heterobifunctional reagent N-succinimidyl 3-(2-pyridyldithio)propionate. Other immunoreagents in our EIA consisted of guinea pig and rabbit antisera to influenza A/Brazil/11/78 (H1N1) for microtiter plate coating and primary antiserum, respectively. The sensitivity of this EIA was tested with 60 clinical specimens containing influenza A/England/333/80 (H1N1) which closely resembles A/Brazil. Of 31 initial specimens, collected within 24 h of the onset of symptoms, 27 (87%) were positive, using a fluorgenic substrate, and 18 of 29 (62%) specimens obtained 12 to 60 h after the initial specimens were positive, for a total of 75% (45 of 60). All positive reactions were specific, as shown in a confirmatory test with preimmune and hyperimmune guinea pig globulins. Clinical specimens negative for virus (n = 33) or containing heterologous respiratory viruses (n = 26) were negative in this system. These results indicate that EIA systems can be developed with a sensitivity approaching that required for clinical usefulness.

Detection and identification of influenza virus antigens by nylon-coupled enzyme-linked immunoassay

A direct solid-phase enzyme-linked immunoassay for rapid detection and typing of influenza virus was developed utilizing antibodies immobilized by covalent linkage to nylon beads. Covalent linkage of antibody to nylon was accomplished by treatment of partially hydrolyzed nylon with glutaraldehyde. For comparison to conventional enzyme-linked immunosorbent assays (ELISA), IgG fractions were adsorbed to polystyrene beads. Influenza type-specific immunoglobulins coupled to nylon beads were used in an enzyme-linked immunoassay to identify influenza A/USSR/77(H1N1), and A/Texas/75 (H3N2). In titrations of viral antigen, antibody coupled to nylon beads detected 1.9 X 10(4) plaque-forming units (PFU) per assay, whereas 2.2 X 10(5) PFU were required in assays utilizing antibody adsorbed to polystyrene beads. Use of fluorogenic or radioactive substrates for alkaline phosphatase-labeled antibodies increased the sensitivity for virus detection 10-fold with this enzyme, but were only slightly more sensitive than chromogenic substrates with peroxidase-labeled antibody.

Enzyme-linked immunosorbent assay for detection of respiratory syncytial virus infection: development and description

An indirect enzyme-linked immunosorbent assay for detection of respiratory syncytial virus (RSV) antigens was developed, using commercially available antisera. Horse anti-RSV and calf antiserum to bovine RSV were used as capture and detector antibodies, respectively. The assay could detect as few as 50 PFU of unpurified RSV per ml in infected cell culture supernatant fluids and as little as 10 ng of affinity-purified RSV antigen per ml. No cross-reactions were observed with heterologous virus types. Freeze-thaw treatment had no effect on RSV enzyme-linked immunosorbent assay titers, but viral transport medium inhibited RSV enzyme-linked immunosorbent assay titers from 10- to 100-fold. The assay can be easily performed in 24 h and is a sensitive and specific method for the detection of RSV antigens.

Enzyme-linked immunosorbent assay for detection of respiratory syncytial virus infection: application to clinical samples

An enzyme-linked immunosorbent assay (ELISA) for respiratory syncytial virus antigens was applied to the rapid diagnosis of acute infections in children and was compared with viral culture and immunofluorescence tests. The ELISA test employed commercially available reagents and was run on a day-to-day basis as specimens were received in the laboratory. Sensitivity and specificity by ELISA were 82 and 95%, respectively, compared with culture. In the same specimens, the sensitivity and specificity by immunofluorescence were 86 and 96%, respectively. Nasopharyngeal aspirates were proven to be a better source of viral antigen than were nasopharyngeal swabs. ELISA-positive samples remained positive even when left unrefrigerated for a week or mailed to the laboratory in plastic containers. Respiratory syncytial virus ELISA, like culture, became negative as the disease progressed and showed no superiority over culture for diagnosis late in the illness.

The role of respiratory syncytial virus and other viral pathogens in acute otitis media

We utilized recently developed enzyme immunoassay techniques to examine the role of selected viruses in the etiology of acute otitis media. Viral pathogens were found in middle ear fluids obtained from 13 (24%) of 53 children with acute otitis media; respiratory syncytial virus accounted for ten of the 13 viral agents identified. In addition, respiratory syncytial viral antigen was found in nasopharyngeal washings obtained from 15 of the 53 children. Seven of these children had RSV identified as the sole middle ear pathogen, whereas six children had otitis caused by Streptococcus pneumoniae as either the sole middle ear pathogen or in combination with RSV. Similarly, all three children with respiratory infections caused by influenza virus had ear infections caused by bacterial pathogens, either alone or in combination with influenza virus. These findings suggest that, in patients with viral respiratory infection, coexisting acute otitis media may be associated with the recovery of either viruses or bacteria from the middle ear exudates.

Enzyme immunoassay for direct detection of influenza type A and adenovirus antigens in clinical specimens

Detection of viral antigens in specimens without prior cultivation in cell culture provides the most rapid method for specific viral diagnosis. A solid-phase, double-antibody enzyme immunoassay was developed for this purpose and tested with clinical specimens containing influenza type A and adenovirus. Polystyrene microtiter wells were the solid phase and were coated with virus-specific guinea pig immunoglobulins. Specimens were added, and bound viral antigens were detected by addition of virus-specific rabbit immunoglobulins followed by enzyme-labeled goat antirabbit immunoglobulin G. Two methods of labeling goat anti-rabbit immunoglobulin G with horseradish peroxidase were investigated: covalent attachment and a noncovalent, immunological binding of antibody to enzyme, the peroxidase-antiperoxidase method. Both methods of labeling resulted in assays that could detect 10(3.5) 50% tissue culture infectious doses of influenza type A and 10(3.8) 50% tissue culture infectious doses of adenovirus. Equal sensitivity was noted with alkaline phosphatase-labeled goat anti-rabbit immunoglobulin G. An increase in sensitivity of three- to sixfold was achieved when virus-specific rabbit immunoglobulins and conjugate were diluted in 1% gelatin. The solid-phase, double-antibody enzyme immunoassay detected influenza type A and adenovirus in isolation-positive clinical specimens with 53% (21/40) and 62% (13/21) efficiency, respectively. The solid-phase, double-antibody enzyme immunoassay has considerable potential as a practical and rapid method for detection of respiratory viral antigens in nasal wash and throat swab specimens. For optimal value, however, greater sensitivity than was provided by the present methods is desirable.

Sudden infant death syndrome associated with rotavirus infection

Rotavirus was detected in the stools of five children stricken with sudden infant death syndrome (SIDS) over a three-week period. While none of the children had acute gastroenteritis, four of the five had acute upper respiratory infections. Rotavirus was also identified in tracheal aspirates from two of the infants. Extensive investigations failed to reveal the presence of any other viruses or toxins in specimens obtained from the five children with SIDS. Rotavirus was not found in the stool specimens obtained from a control group of 36 infants including six who died of causes other than SIDS. Future attempts at the prevention of rotavirus infections should be directed at populations susceptible to sudden infant death syndrome.

Production of antiserum to respiratory syncytial virus polypeptides: application in enzyme-linked immunosorbent assay

By use of crossed immunoelectrophoresis techniques, respiratory syncytial (RS) virus-specific precipitates were produced between RS virus cellular antigen [solubilized in tris(hydroxymethyl)aminomethane-glycine buffer, pH 9] and antiserum raised in rabbits against semipurified RS virus. When these precipitates were employed as antigens for further immunizations in rabbits, antibodies (anti-RSV-precip.I) were produced which reacted with only one RS virus antigen when tested by the crossed immunoelectrophoresis technique. Precipitates obtained between RS virus cellular antigen (labeled with L-[35S]methionine) and anti-RSV-precip.I were examined by polyacrylamide gel electrophoresis, which showed that anti-RSV-precip.I precipitated RS virus polypeptides of molecular weights 28,000 to 84,000. Anti-RSV-precip.I was employed as capture antibodies in the enzyme-linked immunosorbent assay, in which RS virus cellular antigen was used as the second layer. Determination of human RS virus immunoglobulin G antibodies by this enzyme-linked immunosorbent assay technique showed a high degree of sensitivity, specificity, and reproducibility.

Detection of respiratory syncytial virus in nasopharyngeal secretions by inhibition of enzyme-linked immunosorbent assay

An enzyme-linked immunosorbent assay developed for the demonstration of respiratory syncytial (RS) virus immunoglobulin G antibodies was used for the detection of RS virus in specimens of nasopharyngeal secretions (NPS) obtained from children with acute respiratory disease. Samples of NPS were incubated with a fixed amount of standard serum (human serum antibodies to RS virus) before being added to the enzyme-linked immunosorbent assay test plate. A decrease in the optical density value determined for this standard serum was seen with majority of NPS specimens from which RS virus had been isolated in tissue culture. The reliability and the specificity of this inhibiton test were supported by experiments with purified RS virus and by tests with NPS specimens containing other respiratory viruses.

Detection of respiratory syncytial, parainfluenza type 2, and adenovirus antigens by radioimmunoassay and enzyme immunoassay on nasopharyngeal specimens from children with acute respiratory disease

Four-layer antispecies radioimmunoassay (RIA) and enzyme immunoassay (EIA) procedures were developed for the detection of respiratory syncytial virus (RSV), parainfluenza type 2 virus, and adenovirus antigens in nasopharyngeal specimens from children hospitalized for acute respiratory disease. Polystyrene beads (RIA) or flat-bottomed polystyrene microtiter plates (EIA) were used as the solid phases, guinea pig anti-virus immunoglobulins were used as the captive antibodies, rabbit anti-virus immunoglobulins were used as the secondary antibodies, and 125I-labeled sheep anti-rabbit (RIA) or horseradish peroxidase-labeled swine anti-rabbit (EIA) immunoglobulins were used as the indicator antibodies. A comparison of the EIAs and RIAs with routinely used immunofluorescence (IF) techniques was made with 164 nasopharyngeal specimens collected from children with acute respiratory disease. Only 3 of 66 RSV IF-positive specimens were negative in RSV RIA, and of 83 RSV, parainfluenza type 2 virus, and adenovirus IF-negative specimens, 1 was positive in RSV RIA. Of 4 parainfluenza type 2 virus IF-positive and 11 adenovirus IF-positive specimens, each was positive in corresponding RIAs, and all 83 IF-negative specimens were negative in parainfluenza type 2 virus and adenovirus RIAs. The results of the RSV, parainfluenza type 2, and adenovirus EIAs confirmed the results of corresponding RIAs in each selected case tested. The RIAs and EIAs were found to be as specific and sensitive as IF techniques, and more practical in the rapid detection of respiratory viruses in nasopharyngeal secretions.

Detection of influenza A virus by radioimmunoassay and enzyme-immunoassay from nasopharyngeal specimens

Four-layer (indirect) radioimmunoassay (RIA) and enzyme-immunoassay (EIA) techniques were developed for the detection of influenza A and B virus in the sonicated nasopharyngeal specimens from patients hospitalized for acute respiratory infection. Polystyrene beads (RIA) or polystyrene microtiter plates (EIA) were used as the solid-phase, guinea pig antivirus immunoglobulins as the catching antibodies, rabbit antivirus immunoglobulins as the secondary antibodies, and 125I-labeled sheep antirabbit (RIA) or horseradish peroxidase conjugated swine antirabbit (EIA) immunoglobulins as the detector antibodies. A comparison of the developed RIAs and EIAs with the immunofluorescence (IF) method was made with 41 influenza A IF-positive and 150 influenza A IF-negative specimens. Each of the 41 influenza A IF-positive specimens was positive by the influenza A RIA and negative by the influenza B RIA. Out of 150 influenza A IF-negative specimens 3 specimens were found with weakly positive results in influenza A and B RIAs, but in each of these 3 specimens the binding proved nonspecific by the corresponding confirmatory tests. Using the EIa technique and the same immunoreagents as in RIA, identical results were obtained in each selected specimen tested. The developed RIAs and EIAs proved to be as specific and sensitive as the IF technique, and they should be practical in the diagnosis of respiratory infections directly from nasopharyngeal specimens.