Antibody class capture assay (ACCA) for rubella-specific IgM antibody

Performance of two new enzyme immunoassays for the detection of IgM and IgG antibodies to rubella

Two new enzyme immunoassays for detection of rubella-specific IgM and IgG antibodies, Rubaset EIA-M and Rubaset EIA-G, were evaluated. Serum samples from 350 patients with or without rubella symptoms were tested. Rubaset EIA-M had a sensitivity of 98.0%, a specificity of 95.2% and an overall agreement of 96.8% compared with Rubazyme-M. Sera from patients with autoimmune diseases showed no false-positive reactivity. The corresponding values for Rubaset EIA-G were 98.5%, 94.8% and 96.9% respectively, compared with Rubazyme. Sera yielding discordant results were mainly acute-phase specimens from patients with confirmed rubella infection.

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.

Characteristics of different solid-phase immunoassay formats for the measurement of BK virus immunoglobulin M in sera of patients on renal dialysis or with kidney allografts

Solid-phase immunoglobulin M (IgM) antigen capture enzyme immunoassay (AgCEIA) and antibody capture enzyme immunoassay (AbCEIA) were developed for the diagnosis of BK virus (BKV) infections. Of 37 serum samples from renal allograft recipients, 15 were positive for BKV IgM antibody by either AgCEIA, AbCEIA, or antigen capture radioimmunoassay. False-positive IgM results were observed in the AgCEIA in the presence of high levels of BKV IgG antibody (titers greater than or equal to 1:51,200), when rheumatoid factor (RF) titers were greater than or equal to 1:20, or in the presence of high levels of RF (titers greater than or equal to 1:10,240) when BKV hemagglutination inhibition titers exceeded 1:40. False-positives due to RF could be eliminated by treatment of sera with anti-human IgG antisera or IgG-coated latex particles. The presence of RF did not, however, produce false-positive results in the AbCEIA. Both AgCEIA and AbCEIA were specific for BKV IgM antibody, as 14 serum samples containing either JC papovavirus, cytomegalovirus, rubella virus, hepatitis A virus, or hepatitis B virus core IgM antibody were negative in both EIAs. Comparison of results obtained for 37 serum samples revealed 14 positive by radioimmunoassay and 11 positive by both AgCEIA and AbCEIA. Both EIAs detected BKV IgM antibody in sera of renal allograft patients and patients on renal dialysis who had reactivated BKV infections persisting for several months after transplantation.

The detection of measles specific immunoglobulin M antibodies using biotinylated antigens

The methods of reverse type enzymeimmunoassay (EIAs) with biotinylated antigens were used to determine IgM antibodies to measles virus in human sera. These antigens, either purified measles virus antigen or lysate type measles-vero antigen with lysate vero control antigen, were used in the two separate IgM-tests. Paired sera from 15 measles patients as well as 456 sera from patients with viral infections other than measles, with mycoplasma pneumoniae infections, from rheumatoid arthritis patients and blood donors, were assayed in a dilution of 1:200. Both the test systems detected all the 30 serum specimens from the measles patients as measles IgM positive, but the sera of all the other groups proved to be measles IgM negative. These tests developed for measles specific IgM antibodies, avoiding the interference of IgM-class rheumatoid factor, offer valuable tools for routine virus serology.

Use of monoclonal antibodies in an ELISA to detect IgM class antibodies specific for Toxoplasma gondii

Two monoclonal antibodies CH6 and C1E3 were used in an antibody class capture assay for the detection of IgM antibodies specific for Toxoplasma gondii. CH6 was used on the solid phase to capture human IgM. After a Toxoplasma gondii antigen had been added, specifically bound material was detected using C1E3 coupled to horseradish peroxidase. The assay was compared with an established system using polyclonal antisera at both the capture and antigen detection stages. A good correlation was found, with 97.3% (125 of 128) of sera giving the same classification in both assays. Three sera were positive only in the polyclonal system. No false positive results were found when 118 negative sera were examined. The two monoclonal antibodies provide a viable alternative to the use of polyclonal sera at the capture and antigen detection stages in the antibody class capture assay for the measurement of specific IgM against T gondii.

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

A capture enzyme-linked immunosorbent assay (ELISA) for detection of virus-specific immunoglobulin M (IgM) antibody was developed which used a panel of labeled monoclonal antibodies to rubella virus hemagglutinin. The rapidity of the test system was increased by using, after 1-h incubation of the test serum, a second 1-h incubation of the serum with a mixture of viral antigen and labeled monoclonal antibody. The new assay was tested for specificity on 371 human sera from people without any recent contact with rubella virus; of these, 66 were sera selected from people with rheumatoid factor or IgM antibody to human cytomegalovirus, Epstein-Barr virus, or other viruses. In parallel, the new assay was performed on 191 sera from patients having recent contact with rubella virus. Results were compared with those obtained by an indirect ELISA method on IgM serum fractions, using purified rubella virus as a solid phase. Of the 371 sera tested for specificity, 5 (1.3%) gave false-positive results with indirect ELISA (1 rheumatoid factor, 2 heterophil antibody, and 2 human cytomegalovirus sera positive for IgM), and none were false-positive with the capture assay. Two sera from a patient with primary cytomegalovirus infection, which were positive for rubella IgM antibody with both methods and were initially interpreted as false-positive, were finally considered to be true-positive, since they were reactive only in the presence of IgM antibody and viral antigen. Of the 191 sera from 92 patients (84 patients with acute rubella, four newborns from mothers with rubella during pregnancy, and four vaccinees), 136 (71.2%) were found to be positive for IgM by direct ELISA, and 128 (67.0%) were positive by capture ELISA; 12 sera drawn during the first 2 days of disease, or at least 40 days after onset (or after vaccination), were detected only by indirect ELISA, and 4 sera were detected only by capture ELISA. Thus, specificity and sensitivity, respectively, were 100 and 91.4% for capture ELISA and 98.6 and 97.1% for indirect ELISA. However, when the number of patients was considered, 86 were detected as IgM positive by indirect ELISA, and 87 were detected positive by capture ELISA. The overall agreement between the two assays was 96.2%. Capture ELISA using monoclonal antibody appears preferable over indirect ELISA on IgM serum fractions because of its higher specificity and shorter time for test performance; furthermore, there is no need for serum fractionation or virus purification for the capture ELISA.

Assay of measles virus IgM and IgG class antibodies by use of peroxidase-labelled viral antigens

Purified measles virions, nucleocapsid protein and crude lysate of measles infected cells were labelled with horseradish peroxidase, and used for the detection of IgM and IgG antibodies to measles virus by direct enzyme immunoassay. The assays consisted of three layers: anti-human IgM or IgG immunoglobulins on solid-phase, test serum specimen and enzyme labelled viral antigen. For the expression of the results, a standard curve was included in each test and the O.D. values were changed to arbitrary antibody units. Specificity and sensitivity of the assays were compared with indirect EIAs. The specificity studies included a collection of serum specimens containing either rheumatoid factor, antinuclear antibodies or IgM antibody specific for other viruses. The assays proved both reliable and simple to perform and sensitivity was slightly higher than that for indirect EIAs. However, specificity was dependent on the purity of the viral antigens. When crude infected cell lysate antigen was used, some nonspecific results were obtained, particularly with serum specimens containing antinuclear antibodies. When virion or nucleocapsid protein were used, no nonspecific reactions were obtained.

Selection and performance of monoclonal and polyclonal antibodies in an IgM antibody capture enzyme immunoassay for rubella

Monoclonal anti-human IgM and anti-rubella antibodies were prepared and tested in an IgM capture enzyme immunoassay (MACEIA) for rubella-specific IgM and compared with polyclonal reagents. Assay sensitivity was increased with monoclonal antibodies resulting in the improved discrimination of adult sera with low levels of specific IgM. Despite high IgM binding, interference by IgM anti-Ig was not a major problem. The use of monoclonal antibodies allowed assay simplification by the simultaneous rather than sequential addition of antigen and conjugate. Although comparable results were obtained with 33 test samples in the sequential and simultaneous MACEIA, the specificity and sensitivity of this modification requires further evaluation.

Enzyme-linked immunosorbent assay for mumps IgM antibody: comparison of IgM capture and indirect IgM assay

We have established two enzyme-linked immunosorbent assays (ELISAs) for detection of mumps IgM antibody, i.e., indirect IgM ELISA and IgM capture ELISA, for serodiagnosis of recent mumps infection. In the latter method, peroxidase-conjugated monoclonal antibody to mumps virus was employed. Both methods detected mumps antibody of IgM class only in serum fractions separated by centrifugation through a sucrose density gradient. Optical density values given by both ELISAs were correlated for most sera examined. Indirect IgM ELISA, however, gave a false positive reaction for sera containing both rheumatoid factor and mumps IgG antibody, while giving a false negative reaction for sera containing high titers of mumps IgG antibody. This technique was, therefore, less reliable than IgM capture ELISA. IgM antibody detectable by IgM capture ELISA was present in all patients with mumps by the fifth day of illness and persisted for up to 3 mth in most and up to 5 mth in same cases.

Public Health Laboratory Service IgM antibody capture enzyme linked immunosorbent assay for detecting rubella specific IgM

A total of 468 sera were selected for the evaluation of the Public Health Laboratory Service's IgM antibody capture enzyme linked immunosorbent assay kit (MACELISA) for detecting rubella specific IgM. The results obtained were compared with those obtained by IgM antibody capture radioimmunoassay (MACRIA). Sera from patients with primary postnatal rubella, congenital rubella, remote rubella, infectious mononucleosis, and recent infection with other agents were included, in addition to sera taken after rubella immunisation and sera containing rheumatoid factor and rubella specific IgG antibody. The assay exhibited a similar ability and comparable specificity to MACRIA for detecting rubella specific IgM antibody. The Public Health Laboratory Service MACELISA can be recommended if, as for all assays that detect rubella specific IgM, all the available clinical and serological data are taken into account when the results are interpreted.

Detection of specific immunoglobulin M antibody to rubella virus by use of an enzyme-labeled antigen

A direct antibody capture enzyme immunoassay (EIA) for the detection of rubella-specific immunoglobulin M (IgM) antibody was developed. Polystyrene microtiter strips coated with rabbit anti-human IgM were used as solid phase, and a semipurified rubella antigen labeled with horseradish peroxidase was used as indicator. By testing a panel of 238 serum specimens (not including sera from newborns with congenital rubella), the direct EIA was compared with the indirect EIA used routinely in our diagnostic unit and with a commercial IgM capture EIA (RubEnz M II) that employs a horseradish peroxidase-labeled anti-rubella monoclonal antibody as indicator. Overall agreement of direct EIA with indirect EIA and RubEnz M II was 95%, whereas agreement between direct and indirect EIA was 96.2%, and agreement between direct EIA and RubEnz M II was 97.8%. Sensitivity of the direct assay was higher than that of the indirect EIA and similar to that of the RubEnz M II assay. Specific IgM antibody could always be detected in serum specimens taken from patients with primary acute rubella infection between days 4 and 56 after the onset of rash. The assay was highly specific, and it was not affected either by rheumatoid factor or by high levels of specific IgG in sera. Another important advantage that the direct EIA has over the indirect EIA is that it requires 10 to 20 times less antigen per serum specimen tested.

Monoclonal capture antibody ELISA for respiratory syncytial virus: detection of individual viral antigens and determination of monoclonal antibody specificities

An enzyme-linked immunosorbent assay (ELISA) for respiratory syncytial virus (RSV) that employs solid-phase monoclonal antibodies was developed. RSV antigens bound by these monoclonal capture antibodies were detected by addition of a polyclonal bovine antiserum, followed anti-bovine enzyme conjugate and enzyme substrate. The sensitivity and specific of the assay were determined by titrations of the solid-phase antibodies and by antigen titrations with both unpurified RSV-infected cell culture material and purified RSV nucleocapsids. The addition of a competitive binding step prior to the addition of antigen to the solid-phase antibody provides further evidence of the assay's specificity. Furthermore, the competitive binding assay enables the antigen specificity of monoclonal antibodies to be determined or compared without the use of purified antigens. Monoclonal capture ELISA is a convenient, rapid, and sensitive assay that can be used to measure specific RSV antigens in unpurified preparations as well as to determine anti-RSV antibody specificity and should prove useful in examining other complex antigen-antibody systems.

Clinical evaluation of the sensitivity and specificity of a commercially available enzyme immunoassay for detection of rubella virus-specific immunoglobulin M

A solid-phase capture antigen enzyme immunoassay (Rubazyme-M) was evaluated for sensitivity and specificity on sera from 1,200 blood donors, 51 patients with rubella, 2 infants with congenital rubella, 104 patients with other infections, and 126 patients with immunological abnormalities. The sensitivity was 100% for sera tested between days 3 and 40 after the onset of symptoms of rubella virus infection. Rubella virus-specific immunoglobulin M was detected at birth in sera from congenitally infected infants and persisted for several months. Positive Rubazyme-M responses were observed in some patients in the absence of rubella diagnosis (one blood donor, three other infections, and two immunological abnormalities), providing a test specificity of 99.6%. None of 67 patients with rubella virus-specific immunoglobulin G antibody and high levels of rheumatoid factor were positive in the test.

Evaluation of a commercial antibody capture enzyme immunoassay for the detection of rubella specific IgM

A commercial M antibody capture ELISA kit ( Rubenz M) for the detection of rubella specific IgM was evaluated in comparison with M antibody capture radioimmunoassay. A total of 248 sera were evaluated, including sera from cases of primary postnatal rubella, congenital rubella, infectious mononucleosis, and sera which contained rheumatoid factor. No false positive results were obtained but two high positive sera gave Rubenz M values which were below the value recommended as indicative of a positive result. We therefore propose changes in the criteria used for assessing the significance of the results obtained. These changes improve the accuracy of the assay without loss of specificity.

Use of monoclonal antibodies to human immunoglobulin M in "capture" assays for measles and rubella immunoglobulin M

Monoclonal antibodies to human immunoglobulin M (IgM) were used in a four-phase enzyme immunofluorescence "capture" assay for determination of IgM antibodies to measles and rubella viruses. Little or no background reactivity was seen in the test system, and interfering effects of rheumatoid factor were avoided by preabsorption of test sera with aggregated human IgG. Virus-specific IgM antibody was demonstrable in 23 of 24 patients with serological evidence of measles virus infections and in 36 of 36 patients with serological evidence of postnatal rubella infection. A few of the rubella patients did not show IgM antibody until 5 days after onset of illness. The enzyme immunofluorescence assay was able to demonstrate rubella IgM antibody in congenitally infected newborns, whereas indirect immunofluorescence results for virus-specific IgM were negative. Viral IgM antibody was not detected in persons with past infections with the test viruses, in young children without evidence of past infection, or in patients infected with heterotypic viruses, rickettsiae, chlamydiae, or mycoplasmas.