Enzyme immunoassay of mumps virus in cell culture with peroxidase-labelled virus specific monoclonal antibodies and its application for determination of antibodies

Development of a high-throughput assay for measuring serum neutralizing antibody against enterovirus 71

Enterovirus 71 (EV71) is the main etiologic agent of hand, foot, and mouth disease (HFMD) and causes frequently severe neurological complications and mortality in young children. The serum neutralizing antibody response is the major indicator of EV71 infection and protective immunity. The current serum neutralization test based on inhibition of cytopathic effect (Nt-CPE) requires manual microscopic examination, which is time-consuming and labor-intensive. In this study, a high-throughput neutralization assay which employs enzyme immunoassay for detecting growth of EV71 in Rhabdomyosarcoma (RD) cells and measuring serum neutralizing antibody (Nt-EIA) against EV71 was developed. RD cells infected with 100 TCID(50) of EV71 for 36-42h had the best performance and were selected for Nt-EIA. One hundred and twenty human sera (59 negative sera, 61 positive sera) were measured for EV71 neutralization antibody titers by Nt-CPE and Nt-EIA. Neutralization antibody titers against EV71 determined by Nt-EIA had a high sensitivity (100%), specificity (94.9%) and agreement (97.5%) by a qualitative comparison with Nt-CPE. In the quantitative comparison, the correlation coefficient between Nt-EIA and Nt-CPE was 0.91 after log transformation. Overall, the Nt-EIA is a suitable alternative assay for the quantitation of EV71 neutralizing antibody to EV71.

A simplified and standardized neutralization enzyme immunoassay for the quantification of measles neutralizing antibody

A simplified and standardized neutralization enzyme immunoassay (Nt-EIA) was developed to detect measles virus growth in Vero cells and to quantify measles neutralizing antibody. Heat-inactivated sera were diluted serially 4-fold and tested in duplicate. The 50% reduction point (50%RP) of virus growth was calculated using the Reed-Muench formula and the neutralizing antibody titre of test sera was converted into mIU/ml by comparing their 50%RP with that of the international standard serum. The optimal virus input and incubation time were found to be 50-100 plaque forming unit (PFU)/well and 64-72 h, respectively. The simplified Nt-EIA had a good reproducibility with only 3.7-4.2% of duplicate tests having a ratio > 4 in an evaluation of intra assay variation and the coefficients of variance were 2-9% in an evaluation of inter assay variation. In addition, the simplified Nt-EIA had a high sensitivity(98.6%), specificity (100%) and agreement (98.8%) in qualitative comparison with plaque reduction neutralization test (PRNT). In quantitative comparison, the correlation coefficient between Nt-EIA and PRNT was 0.83 without log transformation or 0.77 after log transformation and 90% of 61 positive sera had a ratio < 4 between antibody titre tested by the two methods. The simplified Nt-EIA is thus a suitable alternative to the PRNT for the quantification of measles neutralizing antibody.

Rapid direct diagnosis of mumps meningitis by ELISA capture technique

ELISA capture technique (ELISAc) was carried out using a rabbit hyperimmune serum attached to a solid phase for capturing mumps antigens in cerebrospinal fluid (CSF) in patients with meningitis and/or in supernatants of infected Vero cells. A biotin-labelled rabbit serum prepared from the previous serum was added and the reaction was read by an enzymatic (avidine-peroxidase) reaction by automated reading. The cut-off was calculated in 100 CSFs negative for viruses by conventional diagnosis. The specificity was evaluated in Vero cells infected with 22 CSFs collected from vaccinated children (URABE AM9 attenuated vaccine) who developed meningitis. A guinea pig hyperimmune serum confirmed the specificity. Results in culture correlated with the ELISA capture technique (ELISAc). No cross-reactivity was observed with parainfluenza 1, 2, 3 human reference strains. At least 2.5 ngs of purified mumps proteins were detected corresponding to 10(1.5) infectious particles per ml. ELISAc applied directly to 14 CSFs collected from unvaccinated children with meningitis diagnosed five positive cases, whereas in four cases conventional diagnosis had to be undertaken twice. ELISAc permitted the diagnosis of one additional patient. The test can be carried out in 3 h.

Inhibition of Semliki Forest virus multiplication in L-cells by combinations of interferon and ribavirin as measured by plaque titration and direct enzyme immunoassay

Inhibition of Semliki Forest virus (SFV) multiplication in L-cell monolayers by combinations of mouse interferon (IFN) and ribavirin was measured by plaque titration and by direct enzyme immunoassay of SFV in L-cells. When critically inhibitory quantities of IFN and ribavirin were combined, an additive inhibitory effect was observed in either assay.

Time-resolved fluoroimmunoassays with monoclonal antibodies for rapid identification of parainfluenza type 4 and mumps viruses

Monoclonal antibodies were prepared to the F and M proteins of parainfluenza 4A and 4B and to mumpsvirus to obtain reagents that could be configured into type-specific yet broadly-reactive IFA, EIA, and TR-FIA tests. Several antibodies to parainfluenza 4A also detected subtype 4B, although to a somewhat lower signal, and thus were well suited to generic parainfluenza type 4 tests that were comparable to similar tests previously described for parainfluenza types 1, 2, and 3. Monoclonals to subtype 4B were less able to detect 4A because of high background problems in one or another test. Monoclonals to mumpsvirus F protein were completely type-specific. These antibodies were screened by IFA and EIA for broad reactivity with diverse strains of each virus and were configured into optimized EIA and TR-FIA tests. The all-monoclonal tests were then compared to polyclonal tests in terms of their ability to detect virus in clinical specimens. The all-monoclonal TR-FIA was uniformly the most sensitive, detecting virus in 80% of culture-positive parainfluenza 4A specimens, 67% of parainfluenza 4B specimens, and 90% of mumps specimens, compared to 40-67% for the monoclonal EIA tests and 33-60% for the polyclonal EIA tests. For parainfluenza 4 TR-FIA, mean P/N values were 379 for subtype 4A cell culture fluids (228 for subtype 4B cultures) and 57 for 4A clinical specimens (43 for 4B specimens). For mumpsvirus TR-FIA, mean P/N values were 27 for culture fluids and 32 for clinical specimens. The sensitivities of the TR-FIA were determined with purified virus to be 0.28 ng virus per well for parainfluenza 4A and 0.70 ng virus per well for mumpsvirus.

Blocking ELISA for detection of mumps virus antibodies in human sera

A new blocking enzyme-linked immunosorbent assay (ELISA) for detection of mumps virus (MuV) specific antibodies in large numbers of human serum samples was developed. The blocking ELISA is based on the reaction of MuV-specific, conjugated monoclonal antibodies (mAbs) with immobilized virus antigen, that has previously been incubated with a two-fold dilution of human serum. Mouse hybridomas that produce antibodies against MuV proteins were generated. They could be divided into 4 groups according to their hemagglutination inhibiting- and virus neutralizing capacities and their reaction in the blocking ELISA with MuV strain Enders. Ascites material from 22 mAbs derived from the 4 groups was further characterized with the MuV strains Enders and Jeryl Lynn. When mAbs from different groups were mixed in the blocking ELISA, an additional increase in absorbance could be observed. A mixture of 2 MuV neutralizing mAbs that were directed against HN and F protein, was used to assay 3 consecutive pre-, early post- and late postvaccination serum samples of 138 children, vaccinated at the age of 1.5 yr. A correlation of 94% was found between the blocking ELISA and the normal indirect ELISA, and of 98% between the blocking ELISA and the neutralization enzyme immunoassay (N50-EIA). The specificity and rapidity of the blocking ELISA makes it suitable for routine use in the determination of MuV neutralizing antibodies in large quantities of serum samples.

Rapid detection of mumps virus by the polymerase chain reaction

A procedure for detecting mumps virus in under 48 h was developed using the PCR. The sensitivity of the PCR amplification reaction and of the detection of the PCR product was significantly improved by: (i) enriching for viral template RNAs by overnight culture of the virus in Vero cells and (ii) substitution of polyacrylamide gel analysis for agarose gel electrophoresis. The technique was capable of detecting 1-20 infectious units of virus or an equivalent of 1-10 pg of mumps virus-specific plasmid DNA.

Effect of fixation on the detection of transmissible gastroenteritis coronavirus antigens by the fixed-cell immunoperoxidase technique

The effect of various fixatives and detergents on the in vitro detection of the viral determinants which are expressed in swine testis cells infected with the transmissible gastroenteritis coronavirus (TGEV) was studied using a microwell immunoperoxidase technique. When compared with glutaraldehyde and formaldehyde, 0.1% paraformaldehyde was found to be the fixative of choice for the detection of these determinants on the membranes of infected cells. Among dehydrating fixatives, 80% acetone or a mixture of acetone and ethanol or of acetone, methanol and ethanol were found to be the best fixatives for the detection of these viral determinants which are expressed in infected cells. In the case of acetone, the temperature of fixation and its concentration in the fixative preparation were found to be important. The treatment of 0.05% glutaraldehyde-fixed, infected cells with 0.1% saponin or 0.1% paraformaldehyde-fixed, infected cells with 1%NP-40 led to satisfactory detection of viral determinants. Using Triton X-100 to render cells permeable, the quantities of N and M antigen detected in TGEV-infected cells prefixed with either 0.05% glutaraldehyde or 0.1% paraformaldehyde were equal to those of 80% acetone-fixed, TGEV-infected cells while the quantity of S antigen detected was diminished. The effect of other detergents such as zwittergent, empigen BB, Chaps and N-lauroylsarcosine on the detection of viral determinants was also studied.

Comparison of a neutralization enzyme immunoassay and an enzyme-linked immunosorbent assay for evaluation of immune status of children vaccinated for mumps

A 50% neutralization enzyme immunoassay (N50-EIA) was compared with an indirect enzyme-linked immunosorbent assay (ELISA) for determining mumps virus antibodies in three consecutive serum samples from 138 children vaccinated with a live mumps vaccine at the age (in years) of 1.5. By the N50-EIA, most (132 of 138) preserum samples did not show neutralizing activity. Eight to 12 weeks after vaccination, 17 of the children were still negative, but only 7 remained so after 2.5 years, resulting in a seroconversion rate of 125 of 132 (95%). Over the same period, the neutralization geometric mean titer rose from 3.6 to 9.9. By an indirect ELISA, 128 of 138 preserum samples were found negative. The early and late postvaccination sera of 8 children were ELISA negative, resulting in a seroconversion rate of 120 of 128 (94%). Only two children remained seronegative by both methods. Seven of the late postvaccination serum samples yielded noncorresponding results, reflecting 95% correlation between both methods. Due to cross-reactivity with parainfluenza viruses, the ELISA proved to be less specific, but on the other hand, it showed a greater sensitivity than the N50-EIA.

Efficient induction of Semliki Forest virus and mumps virus neutralizing anti-anti-idiotypic antibodies using Quil A as adjuvant

Rabbit anti-idiotypic sera were prepared against Semliki Forest virus (SFV) neutralizing monoclonal antibody (MAb) UM 1.13 and mumps virus neutralizing MAb UM 10B. From these sera anti-idiotypic antibodies were purified by ammonium sulphate precipitation and subsequent affinity column chromatography. Anti-iso- and anti-allotypic antibodies were removed by binding to normal mouse serum immunoglobulins coupled to CNBr activated Sepharose. Peak protein fractions eluted from columns loaded with homologous MAb were used for anti-anti-idiotypic immunization of BALB/c mice to raise virus neutralizing anti-anti-idiotypic antibodies. Two intracutaneous immunizations, five weeks apart, with affinity purified rabbit polyclonal anti-idiotypic antibody (40 micrograms protein per animal) coupled to keyhole limpet hemocyanin and mixed with the adjuvant Quil A (50 microliters per animal) were sufficient to evoke neutralizing antibodies against either virus. Moreover the mice who developed SFV neutralizing serum antibodies upon anti-idiotypic immunization all survived an otherwise lethal challenge with virulent SFV.

NCI-H292 as an alternative cell line for the isolation and propagation of the human paramyxoviruses

Primary rhesus monkey kidney (MK) cells have long been the cells of choice for isolation and propagation of the human paramyxoviruses (parainfluenza 1, 2, 3, 4A, 4B, and mumps). However, problems with the supply and cost of MK cells and the presence of endogenous viruses, including herpes B virus and SV-5, necessitated a search for an alternative cell line. Continuous cell cultures of human origin (L132, A-549, HuT-292, HEK, G-293, G-401, A-498, A-704, CAKI-1, RD) and simian origin (LLC-MK2, BSC-1, MA-104, Vero) were evaluated for their capacity to support the growth of the human paramyxoviruses, as followed by cytopathic effect, hemadsorption, hemagglutination, and EIA. NCI-H292 (HuT-292) human lung mucoepidermoid carcinoma cells (ATCC # CRL-1848) proved to be the most sensitive line for cultivating all serotypes and strains of the paramyxoviruses. These cells were also shown to be a suitable substitute for MK in primary isolation of paramyxoviruses from clinical specimens. RPMI-1640 with 1.5 micrograms/ml trypsin was the preferred maintenance medium; alternatively, Eagle's MEM supplemented with 1.5 micrograms/ml trypsin and 0.1% ITS was satisfactory. NCI-H292 cells are a continuous line with excellent growth characteristics, although the genetic polyploidy of the cells may limit the number of passages of usable cells.

Competition binding assay in cell culture for identification of epitopes on enveloped and naked viruses

Virus infected monolayers, in wells of 96-well plates, could be used as antigen in competition binding assays to identify epitopes on respectively Semliki Forest virus, encephalomyocarditis virus and mumps virus.