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

Evaluation of rubella IgM enzyme immunoassays

BACKGROUND

Rubella virus generally causes a mild fever, rash illness similar in clinical presentation to infections by other viruses including measles and parvovirus B19. Rubella infections in pregnant women in the first trimester carry a high risk of congenital rubella syndrome (CRS) which can result in severe congenital defects in the infants. The goal of rubella immunization programs is therefore to eliminate CRS. The primary test for the laboratory confirmation of rubella is IgM serology. It is therefore important to evaluate currently available commercial rubella IgM immunoassays to ensure high quality rubella diagnostic testing.

STUDY DESIGN

In this study, we compared the performance of seven commercial rubella IgM enzyme immunoassays (EIA) (Meddens, Denka Seiken, Behring, Wampole, Captia, Sigma and Abbott Axsym) using well-defined panels of sera from rubella and non-rubella/rash-illness cases.

RESULTS

The Meddens, Denka Seiken, Behring and Wampole rubella IgM EIAs all performed similarly for sensitivity (range of 74.1-76.8%) and specificity (range of 93.9-96.1%). Relative to the other assays, the Axsym had a higher sensitivity (78.9%) but lower specificity (86.5%). The Captia assay had the lowest overall sensitivity (66.4%), while the Sigma assay had a lower specificity (85.6%) in relation to the other assays.

CONCLUSIONS

In conclusion, the Meddens, Denka Seiken, Behring and Wampole rubella IgM EIAs are comparable in their overall performance with respect to sensitivity and specificity.

Analysis of immunoglobulin A antibodies to Helicobacter pylori in serum and gastric juice in relation to mucosal inflammation

Helicobacter pylori is a major etiologic agent in gastroduodenal disorders. In this study, immunoglobulin A (IgA) antibodies to H. pylori antigens were evaluated in serum and gastric juice specimens obtained from patients with gastritis or peptic ulcers by utilizing antibody capture enzyme-linked immunosorbent assays (ACELISAs). Urease alpha subunit (UA), urease beta subunit (UB), the 66-kDa heat shock protein (HSP), and the 25-kDa protein (25K) were used as antigens for the ACELISAs. The antibody titers of the ACELISAs reflect the ratio of H. pylori-specific IgA to total IgA. The ratio is stable, although the antibody concentration fluctuates in gastric juice. By using ACELISAs it was possible to evaluate quantitatively not only serum IgA antibodies but also gastric juice secretory IgA (S-IgA) antibodies. In both serum IgA and gastric juice S-IgA ACELISAs, the titers of antibody to HSP and 25K were remarkably correlated with the histologic grade of gastritis, whereas those to UA and UB were not strongly correlated with histologic grade. Thus, it is useful for estimating the histologic grade of gastritis to quantify serum IgA and gastric juice S-IgA antibodies to HSP and 25K.

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.

A practical guide to the diagnosis of congenital infections in the newborn infant

Every attempt should be made to identify an etiologic agent in infants with suspected congenital infection. Some of the infections are treatable, such as herpes simplex, syphilis, and toxoplasmosis. For other infectious agents (i.e., CMV and rubella), close follow-up will enable early detection of hearing impairment and permit early educational intervention. In addition, appropriate isolation measures will reduce the risk of nosocomial infections due to herpes simplex, rubella, hepatitis B, and CMV. Rational use of the available diagnostic tools will enable detection of most symptomatic congenitally infected neonates at a reasonable cost.

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.

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.

Detection of rubella-specific IgM in subclinical rubella reinfection in pregnancy

Seven cases of asymptomatic rubella reinfection in early pregnancy are described. In each, there was a history of exposure to a rubelliform illness and low levels of rubella-specific IgM subsequently appeared in the serum. Four of the women had been immunised, after having been shown to be susceptible to rubella, one had been immunised at school without previous antibody screening, and two were uncertain about immunisation. One pregnancy was terminated and rubella virus was not isolated from the products of conception. Six pregnancies went to term and the infants showed no evidence of intrauterine infection. In a further case it was impossible to discriminate between reinfection and primary infection, and termination of pregnancy was offered.

Comparison of five different methods of rubella IgM antibody testing

Five tests for the detection of rubella specific IgM antibody were compared. They were the conventional method of sucrose density gradient fractionation, followed by haemagglutination inhibition; an anti-mu capture radioimmunoassay; and three commercially available enzyme linked assays: Rubazyme M, Rubenz M I, and its successor, Rubenz M II. The five methods detected similar numbers of rubella positive samples between seven and 35 days after the onset of symptoms; in the earlier stages, however, the radioimmunoassay and Rubenz M II were more sensitive. All three commercial kits were straightforward to use but produced misleading positive results with sera containing heterophil antibody. In considering sensitivity, specificity, and cost effectiveness together the Rubenz M tests were the most appropriate for routine use. With the recent withdrawal of Rubenz M I from the market only Rubenz M II is now available. If Epstein-Barr virus infection is excluded, Rubenz M II provides a reliable test for the diagnostic laboratory.