Development and evaluation of a capture enzyme-linked immunosorbent assay for determination of rubella immunoglobulin M using monoclonal antibodies

Prenatal diagnosis of rubella virus infection by direct detection and semiquantitation of viral RNA in clinical samples by reverse transcription-PCR

A reverse transcription-nested PCR (RT-nPCR) method for prenatal diagnosis of rubella virus (RV) infection was developed. In the first step of RT-nPCR a synthetic RNA molecule (pRRV) differing from the RV target sequence by having a 21-nucleotide insertion was used as the internal control of amplification for the detection of PCR inhibitors. In addition, comparison of pRRV and RV-specific PCR signals allowed for the semiquantitation of RV input target sequences (range, 10 to > and = 1,000 RV genomes). In parallel, a complete RT-nPCR assay was performed with the same samples in the absence of the internal control to confirm the results of the first step and to detect RV RNA-positive samples containing < 10 RV genomes. Subsequently, the RT-nPCR method was used to examine retrospectively clinical samples (direct RT-nPCR) from eight congenitally infected and eight uninfected fetuses for RV RNA. RT-nPCR was also used to detect RV RNA in cell cultures (culture-RT-nPCR) 96 h after inoculation with the same specimens. With amniotic fluid (AF) samples, direct RT-nPCR identified eight of eight cases of RV transmission (sensitivity, 100%), whereas culture-RT-nPCR and virus isolation detected only six of eight cases (sensitivity, 75%). However, when the culture-RT-nPCR results were positive, culture-RT-nPCR confirmed the direct RT-nPCR results 3 days to 3 weeks earlier than virus isolation. The specificity of direct RT-nPCR was 100%, with eight of eight uninfected fetuses being negative. Semiquantitation showed only small amounts (< and = 100 copies) of viral RNA in clinical samples. In conclusion, direct RT-nPCR with AF samples (i) shows 100% sensitivity and specificity for prenatal diagnosis of RV infection and (ii) is a rapid technique, giving results in 24 to 48 h after sampling.

Quantitative detection of secretory immunoglobulin A to Helicobacter pylori in gastric juice: antibody capture enzyme-linked immunosorbent assay

Helicobacter pylori is a major etiologic agent in gastroduodenal disorders. In this study, immunoglobulin A (IgA) antibodies to H. pylori were estimated in serum and gastric juice specimens from patients with gastritis and peptic ulcers using antibody capture enzyme-linked immunosorbent assays (ACELISAs). The antibody titers of the ACELISAs are independent of the antibody concentration and reflect the ratio of H. pylori-specific IgA to total IgA. The ratio is stable, although the antibody concentration fluctuates in gastric juice. Using the ACELISAs it was possible to evaluate quantitatively not only serum IgA (SR-IgA) antibodies but also secretory IgA (SC-IgA) antibodies in gastric juice. There were significant differences between the patients and control group in the SR-IgA and SC-IgA ACELISAs. Furthermore, the ACELISAs made it possible to compare between SR-IgA antibodies in serum and SC-IgA antibodies in gastric juice. In all patients, the ratios of H. pylori-specific IgA were higher in gastric juice than in serum. These results suggest that H. pylori SC-IgA antibodies are mainly produced by the local immune response in the gastric mucosa. Our studies indicate that ACELISA is well suited for the analysis of local immune response in mucosa.

Development and evaluation of capture enzyme-linked immunosorbent assays for detection of immunoglobulin G and M antibodies to group A streptococcal antigens

Capture enzyme-linked immunosorbent assays (ELISAs) were developed to detect immunoglobulin G and M antibodies to group A streptococcal (GAS) antigens, streptolysin O, streptokinase, and group A carbohydrate. The sensitivities and the specificities of the IgM capture ELISAs to each GAS antigen were high enough to distinguish the patients with GAS infections (diagnosed as GAS pharyngitis or scarlet fever) from the control groups (healthy people and patients with pharyngitis from whom GAS could not be isolated). On the other hand, the specificities of the IgG capture ELISAs were not very effective in diagnosis of GAS infections. When the capture ELISA and an indirect ELISA detecting IgM antibodies to group A carbohydrate were compared, false-positive reactions due to rheumatoid factor occurred in the indirect ELISA, but did not occur in the capture ELISA. These results indicate that the capture ELISA works better than the indirect ELISA in detecting the IgM antibody, and that the IgM capture ELISA to GAS antigen provides a rapid and highly reliable serodiagnosis for GAS infections employing only a single serum.

An antibody- and synthetic peptide-defined rubella virus E1 glycoprotein neutralization domain

We previously described a monoclonal antibody (MAb) library generated by infecting BALB/c mice with rubella virus (RV) and selected by an enzyme-linked immunosorbent assay (ELISA) using purified virion targets. Plasmid pARV02-01, which expresses the fusion protein RecA1-35-GIGDLGSP-E1(202)-E1(283)-GDP-LacZ9-1015 in Escherichia coli, was shown to be a ligand for MAbs E1-18 and E1-20 (J. S. Wolinsky, M. McCarthy, O. Allen-Cannady, W. T. Moore, R. Jin, S. N. Cao, A. Lovett, and D. Simmons, J. Virol. 65:3986-3994, 1991). Both of these MAbs neutralize RV infectivity. A series of five overlapping synthetic peptides was made to further explore the requirements of this MAb binding domain. One of these peptides (SP15; E1(208) to E1(239)) proved an effective ligand for both MAbs in the ELISA. Stepwise synthesis of SP15 defined the minimal amino-terminal requirement for binding MAb E1-18 as E1(221) and that of MAb E1-20 as E1(223); the minimal carboxyl-terminal requirement is uncertain but does not exceed E1(239). Immunization of mice and rabbits with SP15 induced polyvalent antibody reactive with SP15, with other overlapped and related but not unrelated synthetic peptides, and with RV. The rabbit anti-SP15 antibody showed neutralization activity to RV similar to that of MAbs E1-18 and E1-20 but lacked hemagglutination inhibition activity. These data define a neutralization domain on E1 and suggest that the RV epitopes conserved by SP15 may be critical for protective host humoral immune responses.

A monoclonal-based IgM capture ELISA for detection of antibodies to 22 and 41 kDa membrane antigens of Toxoplasma gondii

A murine monoclonal antibody which reacts to 22 and 41 kDa Toxoplasma gondii surface antigens was employed in an IgM capture enzyme-linked immunosorbent assay (ELISA). A total of 125 patients' sera were tested in the monoclonal-based assay. When compared with a commercial ELISA test (Abbott Toxo-M EIA) which uses polyclonal anti-T. gondii antibodies, good correlation (Pearsons coefficient r = 0.91) was observed. The specificity of the assay was studied by testing a panel of control sera obtained from healthy individuals and blood transfusion donors; all sera gave negative results. Serum samples positive for T. gondii antibodies were treated with 2-mercaptoethanol (2-ME) to demonstrate the specificity of the test for IgM antibodies. Reactivity of these sera was lost after the treatment. The test is not subject to interference by rheumatoid factor as sera positive for rheumatoid factor were negative in the assay. Reproducibility was good with the coefficients of variation for within-day tests below 10% and not exceeding 18% for day-to-day tests. The monoclonal-based assay is simple to perform and appears to be a viable test for diagnosis of T. gondii infection.

A tube latex test based on colour separation for the detection of IgM antibodies to either one of two different microorganisms

A simple two stage assay was developed for the detection of IgM antibodies to either one of two microorganisms chosen arbitrarily for this study. Salmonella enteritidis and Trichinella spiralis. In the first stage, magnetic polystyrene beads (Dynabeads) coated with anti-mu (mouse) antibodies were incubated with the test material for 45 min to capture the IgM antibodies. In the second stage, indicator latex particles were incubated with the Dynabeads for 30 min and the results read following settlement of the Dynabeads under the influence of a magnet. Two types of indicator particles were used: blue-coloured (sensitized with Trichinella antigen) and red-coloured (sensitized with Salmonella antigen). These were mixed in suitable proportions to form a purple suspension. Reaction of either type of latex particles due to binding to the adsorbed IgM antibodies resulted in the settlement of that particle and hence a change of colour in the suspension to either red (if Trichinella-specific antibodies alone were present) or blue (if Salmonella-specific antibodies alone were present). When applied to the sera (used at 1/10 dilution) of both normal and immunized mice, the assay was positive for all but one (18) immune sera, and negative for all but one (9) normal sera.

Comparison of an antibody-capture IgM enzyme-linked immunosorbent assay with IgM-indirect immunofluorescence for the diagnosis of acute Sindbis and West Nile infections

The development and evaluation of an antibody-capture ELISA for the detection of IgM antibodies to Sindbis (SIN) and West Nile (WN) viruses are described. Comparison of the ELISA results with those obtained by indirect immunofluorescence (IIF) antibody tests using both fluorescein and biotinylated anti-human IgM conjugates, showed that the former technique was both more sensitive and specific than the IIF methods. There were no false positives by the ELISA whereas with the IgM-IIF assays a high percentage of false positives were obtained. These were due to rheumatoid factor and also to an interfering factor which was not detected by the RF latex agglutination test. Absorption of the sera with anti-IgG was necessary to eliminate this interference in the IgM-IIF tests.

A two-particle turbidometric latex immunoassay for the detection of specific IgM antibodies

A simple two stage assay using latex particles as a reaction indicator has been developed for the detection of IgM antibodies to Trichinella spiralis. In the first stage, magnetic polystyrene beads (Dynabeads) coated with T. spiralis antigen were incubated for 30 min with the test serum. After washing, in the second stage, the assay was developed for 1 h using anti-mu-coated latex particles. After sedimentation of the Dynabeads the turbidity of the resultant latex suspension was measured spectrophotometrically at a wavelength of 400 nm. A decrease in turbidity of more than 20% from that of the control, unreacted, suspension was considered positive. Using an IgM phosphorylcholine-binding monoclonal antibody which was reactive with T. spiralis, the sensitivity of the assay was determined to be 110 ng/ml of antibody. This was 20-fold less than the sensitivity achieved in an indirect enzyme-linked immunosorbent assay (ELISA). When the assay was applied to sera obtained from CBA/N or BALB/c mice, which were either normal or immunized against T. spiralis, the expected results were obtained with titers up to 1/640 observed, and confirmed (r = 0.93, P less than 0.001) in the ELISA.

Single-serum diagnosis of recent rubella infection with the use of hemagglutination inhibition test and enzyme-linked immunosorbent assays

Single-serum diagnosis of recent rubella infection was attempted with the use of hemagglutination inhibition (HI) test and two commercially available enzyme-linked immunosorbent assays (ELISAs). The period during which IgM antibody was detectable by IgM capture ELISA was 4 to 30 days after the onset of rash. Rubella IgG ELISA values relative to HI titer were lower in the sera from the patients with recent infection than in the sera from the subjects with remote infection. IgM ELISA and the combined use of IgG ELISA and HI test are two useful methods of single-serum diagnosis of recent rubella infection.