Antibody capture radioimmunoassay for anti-rubella IgM

Diagnosis of fetal rubella infection with reverse transcription and nested polymerase chain reaction: a study of 34 cases diagnosed in fetuses

OBJECTIVE

Our purpose was to develop a reliable method for prenatal diagnosis of fetal rubella infection through the detection of viral ribonucleic acid extracted from the chorionic villi, amniotic fluid, or fetal blood in pregnant women.

STUDY DESIGN

Double amplification of rubella viral ribonucleic acid by nested polymerase chain reaction after reverse transcription was applied to samples from 34 women suspected of having rubella. The results were compared with those of serum antibody and levels of rubella virus-specific immunoglobulin M antibodies in fetal blood.

RESULTS

Viral ribonucleic acid was revealed in 8 of 34 cases (23.5%). In the remaining 26 cases, healthy babies were born in 24, 1 was electively aborted, and 1 died in the thirty-sixth week of pregnancy of unknown causes.

CONCLUSIONS

This method allowed very early detection of fetal rubella infection by sampling of chorionic villi and amniotic fluid compared with evaluation of the maternal symptoms and serum antibody levels. Fetal blood was also more useful for making a diagnosis up to the twentieth week of pregnancy than was measuring rubella virus-specific immunoglobulin M antibodies.

Evaluation of 15 commercial enzyme immunoassays for the detection of rubella-specific IgM

BACKGROUND

Detection of rubella-specific IgM is a critical investigation in the diagnosis of recent or congenital rubella for which many commercial enzyme immunoassays (EIAs) are now available.

OBJECTIVES

To evaluate 15 commercially-available EIA kits for the detection of rubella-specific IgM.

STUDY DESIGN

A panel of 229 sera was established comprising 72 sera from cases of primary rubella, re-infection, congenital rubella and primary immunization in which rubella-specific IgM had been detected by M-antibody capture radioimmunoassay (MACRIA); 80 sera, negative by MACRIA and no evidence of recent illness; 77 sera from recent illness with a number of other microbial agents, sera containing rheumatoid factor, and sera previously shown to give non-specific reactivity by MACRIA. These sera were tested in 15 commercial EIA kits for rubella-specific IgM according to the manufacturers' instructions. Sensitivity and specificity for each assay was established.

RESULTS

Specificities ranged from 82-98%, improving to 88-100% if the previously established non-specific reactive sera were excluded. Sensitivities ranged from 63-92%. Although only two sera from congenital rubella were tested, for one serum only four assays detected specific IgM.

CONCLUSION

Some commercial EIAs for rubella-specific IgM now give an acceptable balance of sensitivity and specificity, but all assays may give reactivity with occasional sera where there is no supporting evidence for recent primary rubella or rubella reinfection.

Multicenter evaluation of a new commercial assay for detection of immunoglobulin M antibodies to Toxoplasma gondii. Multicenter Study Group

A new commercial assay for detection of IgM-specific antibodies to Toxoplasma gondii (IMx Toxo IgM, Abbott, USA), based on microparticle enzyme immunoassay technology, was evaluated at 15 clinical sites in Europe and the USA. Performance characteristics were established by testing clinical specimens collected randomly from pregnant women, blood donors, individuals with suspected Toxoplasma gondii infection and individuals confirmed HIV positive. Reference testing was performed using Toxo-M EIA (Abbott). Specimens evaluated at European sites yielding discordant results between the new assay and the reference EIA were further tested with an immunosorbent agglutination assay; at sites in the USA, discordant results were resolved using Platelia Toxo IgM (Sanofi, France) and Vidas Toxo IgM (bioMérieux, France) assays. In addition, matched plasma and serum, heat-treated and non-heat-treated specimens, and fresh and frozen specimens were evaluated at the USA sites. At European sites the new commercial assay had a sensitivity of 95.6% (196/205), a specificity of 99.8% (3,137/3,143) and an agreement of 99.6% (3,333/3,348) following resolution of discordant results; sensitivity in the USA was 97.4% (184/189), specificity was 99.8% (1,204/1,207) and agreement was 99.4% (1,388/1,396) following resolution. The new IMx Toxo IgM is a sensitive and specific assay for measurement of IgM antibodies to Toxoplasma gondii in human serum and plasma.

Comparison of two immunoassay procedures for detecting enterovirus IgM

Enteroviruses cause significant illness in man but viral diagnosis is problematic. Enterovirus-specific IgM tests have been developed but due to the difficulties of obtaining reliable control sera the interpretation of assay data remains mainly arbitrary and empirical. The present study was undertaken to assess the reliability of such assays by comparing two tests performed independently in two different laboratories: a mu-capture radioimmunoassay (MACRIA) which utilizes 35S-labelled Coxsackie virus antigens and an enzyme immunoassay (EIA). A feature of the MACRIA was that sera were tested in one large batch whereas the EIA was in routine use in a reference laboratory. The MACRIA was easy to perform but more suitable for research investigations than routine diagnostic use. Similar results were detected in the majority of sera tested in the two assays with 85% concordance achieved on testing 120 sera. Of the 18 discrepant results, 11 were positive by EIA only and 7 by MACRIA only. 89-95% concordance was obtained on testing sera against individual Coxsackie B1-5 serotypes, moreover 52% of the sera positive in MACRIA were reactive against only one viral antigen and the results on certain of the more strongly reactive sera suggested the existence of a measure of type specificity in the MACRIA test. Qualitative differences between the two tests highlighted problems of interpretation in the absence of a gold standard and cautioned against sole reliance on serology for diagnosis of enteroviral infections.

Comparison of four enzyme immunoassays for detection of immunoglobulin M antibodies against rubella virus

We evaluated four tests for the detection of rubella virus-specific immunoglobulin M antibodies. Primarily, consecutive serum samples were tested by two different assays. Selected panels of sera from patients with proven or likely recent rubella and false-positive and true-negative results in the two primary assays were further tested with two recently developed, fully automated techniques. The four tests were comparable in overall accuracy, but their dynamic ranges may differ considerably. Ways to optimize the predictive values are discussed. We conclude that automated assays may be used without causing significant changes in diagnostic accuracy or distortions in notifications of the incidence of rubella compared with the use of established tools.

Slow maturation of IgG1 avidity and persistence of specific IgM in congenital rubella: implications for diagnosis and immunopathology

Without appropriately timed specimens, serological confirmation of congenital rubella infection may be a problem. We have compared the persistence of specific IgM and low avidity specific IgG1 in 141 sera from 120 cases of serologically confirmed congenital rubella infection with the known time scales for postnatal primary rubella. The results demonstrate that the maturation of the immune response to the rubella virus is abnormally slow in congenital rubella cases both in terms of the isotype switch and especially the development of high avidity specific IgG1. Thus avidity studies may permit serological confirmation of congenital rubella for longer than is possible with tests currently in use. The pathological implications of prolonged low avidity antibody production are discussed.

Detection of measles, mumps, and rubella antibodies in saliva using antibody capture radioimmunoassay

Antibody capture radioimmunoassays were developed for detecting virus specific IgM (MACRIA) and IgG (GACRIA) to measles, mumps, and rubella and used to investigate saliva as an alternative specimen to serum for diagnosis. Saliva was collected from 63 patients with measles, 19 with mumps, and 150 with rubella, which were all clinically diagnosed and serologically confirmed. Virus specific IgM was detected in 92% of measles, 75% of mumps, and 100% of rubella saliva samples collected during the first week of illness. Between 1 and 5 weeks after onset virus specific IgM was detected in 100% of saliva specimens. After the 5th week the proportion of reactive specimens declined. The specificity of the MACRIA tests was established by testing saliva samples collected from blood donors for measles (88), mumps (88), and rubella IgM (91). All of the saliva specimens tested for measles and rubella specific IgM were unreactive, 1/88 specimens tested for mumps specific IgM contained significant reactivity. Saliva specimens collected from acute cases of MMR were tested in all 3 MACRIAs. A small proportion of saliva samples contained detectable IgM of more than one virus infection. Rubella and measles specific IgG was detected in the saliva of all cases from the 4th or 5th day of illness, respectively. Detection of mumps specific IgG was less successful. We have demonstrated that virus specific IgM can be reliably detected in saliva samples collected from acute cases of measles, mumps, and rubella and identified 1-5 weeks after onset of illness as the optimum time for collection of samples.

Persistence of specific IgM and low avidity specific IgG1 following primary rubella

Persistence of specific IgM in sera following primary rubella infection was compared with the maturation of the specific IgG1 response. 206 sera, from 171 patients with primary rubella, taken 1 day to 2.5 years after onset of illness, were tested. Rubella-specific IgM was detected by M-antibody capture radioimmunoassay in 100% of sera taken 15-28 days after onset, but in only 9% taken 3-4 months after onset. However, using the diethylamine (DEA) shift value (DSV) method, low avidity specific IgG1 was detected in 91% sera taken at 3-4 months and at 5-7 months 21% of sera remained positive. Using an avidity index method, with urea in the wash buffer, none of the sera were positive for low avidity specific IgG1 beyond 3 months after onset. With DEA in the wash buffer, the number of sera positive rose to 38% at 3-4 months. Thus, the DSV method for detecting low avidity specific IgG1 is a useful additional test for confirming or refuting a diagnosis of primary rubella and is of particular value for assessing pregnant patients.

Persistent rubella-specific IgM reactivity in the absence of recent primary rubella and rubella reinfection

Between two and seven sera from cases of persistent detection of rubella-specific IgM for periods in excess of 2.5 months, but in the absence of recent primary rubella or rubella reinfection, were examined for rheumatoid factor, heterophile antibody, and IgM reactivity against toxoplasma and a number of viruses. The relative avidity of the rubella-specific IgG1 has been assessed in all the sera by two methods. None of the sera contained rheumatoid factor or heterophile antibody, nor did any contain detectable concentrations of IgM specific for any of the panel of antigens apart from five sera which contained low concentrations of IgM specific for some coxsackieviruses B. No sera were positive for low avidity specific IgG1 although three did give equivocal results with one avidity test and one gave equivocal results with the second avidity test.

Evaluation of commercial enzyme linked immunosorbent assay for detection of B19 parvovirus IgM and IgG

An indirect enzyme linked immunosorbent assay (ELISA) (Parvoscan-B19; Sweden) was compared with an in-house MACRIA for the detection of B19 specific IgM. A Parvoscan-B19 IgG test was also evaluated for its ability to detect a recent B19 infection in paired sera. Two hundred and twenty sera submitted to the laboratory for B19 serology and four MACRIA positive control sera were assayed for B19 IgM. Confirmation of the response of sera giving discordant results in the two assays was sought by the use of a "nested" polymerase chain reaction (PCR) for the detection of B19 DNA. The Parvoscan-B19 IgM test was 79% sensitive and 96% specific. Parvoscan-B19 was poor at detecting parvovirus infection in sera collected two to three months after the onset of symptoms. When sera collected more than seven weeks after the onset of symptoms were excluded from the analysis, Parvoscan-B19 IgM was 84% sensitive and 96% specific. Rubella specific IgM positive sera, rheumatoid factor positive sera, and heterophil antibody positive sera were also assayed for B19 IgM. No false positive results were encountered with these problematic sera. By using the cut off criteria for the Parvoscan-IgM test previously advocated by the manufacturers, 90% sensitivity and 87% specificity could be achieved. False positive results, however, occurred with six of the 17 rubella IgM positive sera, four of the 10 rheumatoid factor positive sera, and two of the 11 heterophil antibody positive sera tested. It is concluded that the Parvoscan-B19 was specific but insensitive when compared with in-house assays.

Laboratory diagnosis of rubella: past, present and future

Fifty years ago in New South Wales the late Sir Norman Gregg [1] described congenital cataracts in 78 babies, 67 of whose mothers had had clinical rubella in early pregnancy; he concluded that the disease in the mother caused the abnormality in the baby. Gregg [1–3] and Swan [4, 5] and their colleagues reported that deafness, heart disease and microcephaly were also major components of the congenital rubella syndrome. The need to prevent this tragic outcome stimulated intensive work on laboratory diagnosis and vaccine development, leading to the isolation of rubella virus in 1962 and then to methods for antibody detection. These complementary advances established the two traditional pillars of virological diagnosis and opened the way to immunization, with the result that some countries are now on the verge of eliminating a disease which for over 100 years was regarded as no more than a mild and harmless exanthem of childhood.

A method for the rapid purification of serum IgM for the diagnosis of recent viral infections of chickens

The rapid purification of chicken IgM from serum was achieved by affinity chromatography. IgM immunoadsorbent gels were prepared using monoclonal antibodies specific to chicken IgM. Five different eluting agents were compared for the dissociation of the adsorbed IgM; the most convenient for routine purposes was 2 M NaCl, Tris-HCl, EDTA (NTE), as this enabled direct assay of eluents by ELISA without requiring the intermediate step of dialysis, which the other eluting agents did. Eluents prepared from sera obtained from infectious bronchitis virus (IBV) and infectious laryngotracheitis (ILTV)-infected chickens, together with samples of the same serum fractionated by gel chromatography, were tested by ELISA for virus-specific antibodies and to confirm the identity of the antibody class. In the case of both IBV and ILTV, similar results were obtained using immunoaffinity and gel chromatography. IBV-specific IgM, as determined by both methods in the ELISA, reached its highest concentration at the 8th day after inoculation and was virtually absent by the 24th day, whilst the highest concentration of ILT-specific IgM was detected at 6 days and no or little IgM was present at 16 days after inoculation. Purification of serum IgM by affinity chromatography followed by ELISA was considered suitable for routine serological diagnosis of IB and ILT, since the time required to complete the assay (3 hours) was considerably less than that for gel chromatography and many samples could be assayed simultaneously.

The avidity of specific IgM detected in primary rubella and reinfection

An IgM capture enzyme-linked immunosorbent assay for rubella-specific IgM was used to assess the avidity of specific IgM by comparing the results obtained with and without a mild protein denaturant in the washing fluid used after incubation of IgM with rubella haemagglutinating antigen. An avidity index (AI) was calculated with AIs less than 50% considered to indicate low avidity. Sera from recent primary rubella, rubella reinfection and from patients persistently reactive for specific IgM were tested. Urea and diethylamine (DEA) were compared as the protein denaturants. Twenty-six of 28 sera from cases of primary rubella gave an AI less than 50% with DEA, compared with 25 of 28 with urea. Seventeen of 20 sera from cases of reinfection gave an AI greater than 50% with DEA whereas only 14 of 20 had a similarly high avidity with urea. Eight of 10 sera from 4 cases of persistent specific IgM reactivity gave AIs greater than 50% with DEA, although this was reduced to 5 when urea was used. Thus a difference has been demonstrated between the avidity of specific IgM in primary infection from that demonstrated after a secondary antigenic challenge (reinfection). This may help in serologically distinguishing primary infection from reinfection.

Development of a highly specific and sensitive rubella immunoglobulin M antibody capture enzyme immunoassay that uses enzyme-labeled antigen

An enzyme immunoassay (EIA) for serum immunoglobulin M (IgM) antibodies to rubella virus based on enzyme labeling of viral antigen was developed. The sensitivity of the EIA for the detection of recent rubella virus infection was evaluated by using 115 rubella-IgM-antibody-positive serum specimens, which were confirmed as positive by Rubazyme M (Abbott Diagnostics). In addition, 12 individuals, 2 of whom were exposed to rubella through vaccination and 10 of whom were exposed through natural infection, were studied, and the results were compared with those obtained by indirect EIA (Rubelisa M; Electro-Nucleonics, Inc.) and immunoblotting. The sensitivity of the newly developed EIA with sera from these individuals was 100%. Serum specimens from two patients indicated that the IgM antibodies were detected by the newly developed EIA at the same time as IgM antibodies were detected by immunoblotting and before positive reactions were detected by an indirect EIA. The reference population consisted of 564 healthy blood donors and hospitalized patients (150 serum specimens). In addition, 145 serum specimens commonly giving false-positive reactions in conventional rubella IgM EIAs were studied. With these specimens, no false-positive reactions were observed. Positive IgM responses, which could not be confirmed by immunoblotting, were observed in two samples from the reference population. However, these two samples were rubella IgG positive. The overall specificity of the EIA was 99.8%.

Detection of immunoglobulins G and M to rubella virus by time-resolved immunofluorometry

We describe new methods for the detection of immunoglobulin G (IgG) and IgM rubella-specific antibodies in serum. The IgG assay was based on a solid-phase rubella antigen immobilization approach, and the IgM assay was based on the IgM capture assay principle. Both assays used biotinylated antibodies (anti-human IgG and antirubella monoclonal antibody, respectively). The tracer system was based on streptavidin labeled with a fluorescent europium chelate. The final measurements were done by using time-resolved fluorescence. Both assays were thoroughly evaluated with clinical samples and compared successfully with established techniques. We anticipate that these assays are suitable for routine clinical use.

Laboratory diagnosis and clinical significance of rubella in children with cancer

Virus-specific antibody responses were studied in 12 children with cancer in whom rubella was diagnosed by seroconversion or a rising titre (greater than or equal to fourfold) of haemagglutination inhibiting (HI) antibody. Our results confirmed the difficulties of making a diagnosis of rubella infection in immunocompromised children using criteria for interpreting antibody assays established in immunocompetent patients. Specific IgM antibody persisted for more than 2 months in 7 of 10 children with probable primary rubella, 3 of whom had high concentrations of such antibody 6, 7 and 11 months after the rash. Radial haemolysis and specific IgG1 and IgG3 antibody responses were low in 4, 2, and 4 patients, respectively. One child apparently had a rubella reinfection and, in another, rubella antibody passively acquired from blood transfusions was probably responsible for the HI seroconversion. Nonetheless, the benign clinical course of rubella in immunocompromised children was confirmed.

Detection of rubella virus in fetal and placental tissues and in the throats of neonates after serologically confirmed rubella in pregnancy

From 35 therapeutic abortions performed because rubella had occurred at 2-19 weeks of pregnancy, 120 fetal organs, 12 specimens of mixed products of conception, and 15 placentae were tested for rubella virus. Virus was isolated from 10 out of 11 fetuses (91 per cent) from women infected at 2-8 weeks, from 5 out of 8 (63 per cent) infected at 9-10 weeks, and from 2 out of 16 (13 per cent) infected at 11-19 weeks. Hybridization tests for viral RNA on 39 fetal organs from eight cases revealed infection in four additional fetuses. Virus was isolated from only 3 out of 15 aborted placentae, but hybridization tests on six placentae revealed infection in three additional specimens. Hybridization was superior to virus isolation for detecting rubella infection in products of conception and is therefore potentially the better method for examining chorionic villus biopsies. Rubella virus was isolated from the throats of 4 out of 9 infants (44 per cent) infected during the first 12 weeks of gestation, but from none of 13 infected after 17 weeks. Infants in the latter group are unlikely to infect susceptible contacts.

Rubella-specific IgG subclass avidity ELISA and its role in the differentiation between primary rubella and rubella reinfection

An antiglobulin enzyme-linked immunosorbent assay for rubella-specific IgG1 and IgG3 was adapted to measure antibody avidity by incorporating a mild protein denaturant, diethylamine (DEA), into the serum diluent. Sera were tested at varying dilutions, both with and without DEA, if they contained sufficient specific IgG1 or IgG3. The optical density (OD) was measured and curves were plotted. The highest OD (V) was noted and halved (V/2). The distance between the OD curves at V/2 was measured as the DEA shift value. Sera were examined from people whose sera contained rubella-specific antibodies as a consequence of infection or vaccination in the distant past (24 sera), recent primary rubella (66 sera), symptomatic reinfection (11 sera) or asymptomatic reinfection (64 sera). For specific IgG1 the DEA shift value was less than 0.6 for cases of rubella in the distant past, compared with greater than 0.8 for the first month after primary infection. The maximum DEA shift value for the sera from cases of reinfection was 0.65. No serum from cases of rubella in the distant past contained sufficient specific IgG3 to estimate avidity. The sera collected within 1 month of onset of primary rubella gave DEA shift values greater than 0.7 compared with sera from reinfections, which gave DEA shift values less than 0.6, except for two sera from a case of symptomatic reinfection. Thus the assessment of specific IgG subclass avidity is of value in differentiating serologically primary rubella from reinfection.

Outcome of confirmed periconceptional maternal rubella

61 pregnant women in whom confirmed rubella occurred from 5 weeks before to 6 weeks after the last menstrual period (LMP) were followed up prospectively. In 39, the pregnancy was terminated and the fetal tissues or mixed products of conception were examined for rubella virus. In 22, the pregnancy continued to term and cord serum was tested for specific IgM antibody. No evidence of intrauterine infection was found in 38 pregnancies in which the mother's rash appeared before, or within 11 days after, the last menstrual period. The shortest interval at which fetal infection occurred was when the rash appeared 12 days after the last menstrual period. All 10 pregnancies in which the rash appeared 3-6 weeks after the last menstrual period resulted in fetal infection: 4 of these pregnancies went to term, and all 4 infants were damaged. The risk to the fetus when rubella occurs before the mother's last menstrual period is probably negligible.

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.

Specific IgG subclass antibody in rubella virus infections

A solid-phase antigen enzyme-linked immunosorbent assay (ELISA) was developed for the detection of rubella-specific IgG subclasses. For rubella-specific IgG1 and IgG3 sera were quantitated in arbitrary units (au) by comparison with standard curves. A concentration of 3 au was taken as that indicating positivity for specific IgG1 and specific IgG3. No sera reactive for specific IgG2 and IgG4 have been found, and thus the assay reagents were controlled by testing dilutions of a standard calibrant serum containing known concentrations of the specific IgG subclasses. Of 105 unselected sera negative for rubella antibody by radial haemolysis (RH), two gave concentrations of specific IgG1 greater than 3 au and both were positive by rubella latex agglutination (LA). The sensitivity of the assay for specific IgG1 was confirmed by examining 25 selected sera negative by RH but reactive by LA. Twenty-one gave concentrations greater than 3 au. None of these 130 was positive for specific IgG3. All 63 sera containing greater than 15 international units rubella antibody by RH from cases of rubella in the remote past contained specific IgG1 and eight contained specific IgG3. In 79 cases of primary rubella, specific IgG1 developed in all cases by day 8. Specific IgG3 became detectable in all cases except one by day 16. Serum taken on day 21 from one case was negative for specific IgG3 but the absence of later sera precluded further investigation. One case had become negative for specific IgG3 by day 56. Sera from 24 cases of rubella reinfection were examined and all contained specific IgG1. In three cases of symptomatic reinfection, specific IgG3 was detectable in two but not in the remaining case. In 2 of the 21 cases of asymptomatic reinfection only a very early or a very late serum was available. Of the remaining 19 cases, 7 had detectable specific IgG3. However, only one of 9 sera collected 30-50 days after contact contained specific IgG3. Thus for the asymptomatic patient for whom other serological tests suggest a recent rubella infection, the failure to detect specific IgG3 in sequential sera collected after contact suggests reinfection rather than primary rubella. The detection of specific IgG3 did not correlate with the presence of specific IgM. Sera collected 6-8 weeks after rubella vaccination had detectable specific IgG1 in 32 of 33 cases and specific IgG3 in 9 of 33. The remaining vaccinee was seronegative.

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.

Serological study of rubella-like illnesses

We investigated 627 patients who within a period of 2 1/2 years had had a rubelliform rash and/or symptoms of arthritis and arthralgia. Sera from these patients were investigated for evidence of rubella, human parvovirus B19 (HPV), and measles infection with methods to detect specific IgM and IgG antibodies. Complement fixation tests were used to screen for a wide range of other infectious agents. We detected 229 cases of rubella, 43 cases of HPV infection, 7 cases of measles, and 9 cases of infection by various other aetiological agents. This left a large proportion of rubelliform rashes, 54% (339 cases), whose aetiology was unknown. This study confirmed that the diagnosis of rubella on clinical grounds alone is unreliable. Many (6.8%) of the rashes in the study were due to HPV infection, and the seasonal incidence was the same as for rubella. There was considerable overlap between the features of rubella and HPV infections, although in adults arthralgia occurred more frequently in HPV infections than in rubella. In all cases HPV infection was self-limiting, although, as in rubella, symptoms can be prolonged and one adult's disease lasted almost 9 months. Purpura was noted in only one patient with HPV infection. In this study three patients had HPV infection during pregnancy. Two patients spontaneously aborted one month later. The third patient progressed to full term and delivered a healthy baby.

The development of an M antibody capture ELISA for rubella IgM

An M antibody capture enzyme-linked immunosorbent assay for rubella IgM was developed. The enzyme label was prepared from a monoclonal antibody raised against rubella haemagglutinin (Tedder et al., 1982). Paired sera from acute rubella infections and vaccines as well as sera from blood donors, antenatal patients and patients whose sera contained rheumatoid factor and patients with acute non-rubella infections were tested by this method.

Separation of hemagglutination-inhibiting immunoglobulin M antibody to rubella virus in human serum by high-performance liquid chromatography

High-performance liquid chromatography was successfully used to separate hemagglutination-inhibiting immunoglobulin M (IgM) rubella virus antibody from IgG rubella virus antibody in human serum. The fractionation by high-performance liquid chromatography was as effective as sucrose density gradient centrifugation in separating IgM antibody from IgG antibody.

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.

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.

Fluoroimmunoassay for detection of rubella-specific immunoglobulin M: comparison with indirect enzyme immunoassay and mu-chain capture

The performance of a commercially-available method of fluoroimmunoassay (Rubella M FIAX, International Diagnostic Technology, Santa Clara, Calif.), designed for the detection of rubella-specific immunoglobulin M, was tested with 137 selected sera, including 52 from cases of primary rubella, 29 from healthy pregnant women, 21 containing rheumatoid factor, and 35 from cases of infectious mononucleosis (IM) caused by Epstein-Barr virus. The results were compared with those obtained by commercial indirect enzyme immunoassay (EIA) and EIA anti-mu chain capture tests. The fluoroimmunoassay technique showed a satisfactory level of sensitivity, but low values had to be interpreted with caution as false-positive results were detected with sera with rheumatoid factor and from IM cases, even after preliminary treatment of sera with the anti-human immunoglobulin G antisera provided in the kit. On the other hand, no false-positive results in the analysis of IM sera were seen in the EIA anti-mu chain capture method. Because of its sensitivity and specificity, we recommend the use of the latter technique for the diagnosis of primary rubella.

Comparison of various serological methods and diagnostic kits for the detection of acute, recent, and previous rubella infection, vaccination, and congenital infections

The antibody development after natural rubella infection and rubella vaccination has been followed in 802 sera from 493 patients and 71 sera from 22 vaccinees. Also examined were 67 sera from 28 infants with rubella embryopathy and sera from 50 children with presumed prenatal infection. In addition, 777 sera from 641 patients tested for routine rubella diagnosis were studied. Anamnestic information was available from all these patients. These sera were assayed for IgM antibody detection by sucrose density gradient (SDG), the commercial ELISAs (Enzygnost IgM and Rubazyme M), and the non-commercial anti-my-hemadsorption immunosorbent technique (HIT). For the determination of IgG antibodies the hemagglutination inhibition test (HAI), the commercial ELISAs (Enzygnost IgG, Rubazyme), and a single radial hemolysis test (SRH) were used. The SDG and HIT were less sensitive for IgM antibody detection than the two ELISAs, particularly when IgM concentrations were low. In total 26.5% of the IgM results with the newer tests were discordant with SDG, but only 0.5-1.3% of these results were not explicable when the clinical data was considered. Problems were encountered with all IgM assay systems used. For the detection of rubella antibodies after acute infection and vaccination the ELISA Enzygnost IgG was as sensitive as the HAI whereas the ELISA Rubazyme and SRH detected antibodies with some delay. Corresponding results with all tests were found more than 25 days after acute infection and more than 50 days after vaccination. All methods can be used for detection of antibodies in infants with rubella embryopathy. The results of this study suggest that certain combinations of tests can be used for the reliable detection of rubella infection.

Evaluation of commercial methods of enzyme immunoassay (EIA) for the measurement of rubella-specific IgM

Four commercial EIA methods for measuring rubella-specific IgM (three indirect tests and one anti-mu capture test) were evaluated, using sucrose gradient centrifugation and hemagglutination inhibition as the reference method. Evaluation was conducted with the aid of four serum panels, including 53 primary rubella cases, 30 healthy pregnant women, 21 sera positive for rheumatoid factor(s) (RF) and 35 sera from 29 cases of heterophil-positive infectious mononucleosis with EBV-specific IgM detected by immunofluorescence. All EIA methods were more sensitive than the reference method when applied to very early samples (1-5 days post-exanthema) and no differences in sensitivity were found between them. On the other hand, we observed a significant incidence of false-positive results if an indirect EIA method is applied to RF-positive samples. False positivity is significantly reduced, but not totally eliminated, when samples are preabsorbed with anti-human IgG serum and, in all cases, the absorbance values obtained were low. In contrast, there were no false-positive results using an anti-mu capture method, even in sera from cases of infectious mononucleosis. The basis for choosing between an indirect method and an anti-mu capture method for the diagnosis of congenital and post-natal rubella virus infection is discussed.

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.

Comparison of the performance and reproducibility of various serological methods and diagnostic kits for the detection of rubella antibodies

For rubella antibody detection performance and reproducibility of standard laboratory methods and newer assay systems have been evaluated. IgM antibody detection in sucrose density gradient ultracentrifugation (SDG) was compared with two commercial ELISAs and the non-commercial anti-my-hemadsorption immunosorbent technique. The two ELISAs proved to be more sensitive than the SDG even if done with a long incubation hemagglutination inhibition test (HAI) to increase sensitivity. Additional tests showed that the sensitivity of the SDG could be increased by using ELISA instead of HAI. The reproducibility of all tests was good. In 205 assays the ELISA enzygnost IgM showed a coefficient of variation (CV) with its reference serum of 6.3% for titers, while the CV for absorbance was 37.8%. With ELISA rubazyme M the same reference serum gave a CV of 13.7% in 149 subsequent assays. In 12 and 13 assays in the anti-my-hemadsorption immunosorbent technique the CV varied with the height of the reference serum used between 4.7 and 18.7%. Antibody detection using HAI was compared with IgG antibody detection using two commercial ELISAs and a commercial single radial hemolysis test (SRH). In 592 assays with a low positive control serum the HAI gave a CV of 6.0%. With the ELISA enzygnost a CV of 7.7% for the titers was obtained in 72 assays, but for absorbances the CV was 39.4%. The CV for the kit internal low positive control in 148 assays with the ELISA rubazyme was 26.8%. As with HAI the reproducibility of the SRH was good. The same control serum used in the HAI gave a CV of 6.2% in 418 subsequent assays. Because of the good reproducibility and sensitivity the SDG can now be replaced by newer techniques which are less expensive and time consuming. Interference with rheumatoid factor was only observed in the ELISA enzygnost if sera were not pretreated with latex adsorbents. The reproducibility of our HAI was comparable to that of the SRH while the results obtained with the two commercial ELISAs were less reproducible. Until it is known, that antibodies detected with the newer techniques are able to prevent re-infection, it would be unwise to reject the HAI completely for the determination of immunity status.

A micro-capture ELISA for detecting Mycoplasma pneumoniae IgM: comparison with indirect immunofluorescence and indirect ELISA

A mu-capture ELISA was developed for detecting Mycoplasma pneumoniae-specific IgM, and compared with an indirect immunofluorescent antibody (IFA) technique and an indirect ELISA. mu-capture ELISA and IFA compared well and were found to be the most sensitive assays. The IFA test can be completed in 2 h whilst the results of the mu-capture ELISA can be available in 24 h. Both tests are amenable to routine diagnostic use and have similar sensitivity. Indirect ELISA was found to be less sensitive and less specific, giving high assay values with several sera having undetectable M. pneumoniae CF antibody or CF antibody in low titre. Serum samples obtained from 11 patients at various times after M. pneumoniae infection showed maximum antibody levels within the first month by all assays, with a gradual fall in amount of IgM with time when assayed by mu-capture ELISA, a more gradual decline by IFA and hardly any decline with indirect ELISA. It was concluded that the indirect ELISA is unsuitable for the investigation of possible M. pneumoniae infection because the sustained high assay values with serum samples taken many months after infection, make interpretation of the test results very difficult.

Clinical validation of an antibody-capture anti-rubella IgM-ELISA

An antibody-capture IgM-ELISA using monoclonal antibodies for conjugate was subjected to clinical validation with respect to sensitivity and specificity. In 103 serum specimens, known to contain anti-rubella IgM by a sucrose density gradient method, IgM was found by the ELISA in 99 sera. In a second study, 16 out of 17 acute rubella infections were detected by the IgM-ELISA. In 17 out of 17 vaccinees, a specific IgM response could be demonstrated. Specificity of the antibody-capture ELISA was found to be high; no interference was seen in 60 rheumatoid-factor positive sera, in 100 highly positive IgG sera or 10 sera with anti-CMV IgM. Only one out of 100 sera with heterophile antibodies showed a positive response. In acute rubella infections, IgM was shown to be detectable from 1 to 4 days after onset of illness up to about 12 wk, with peak values at about 1 wk after onset.

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.

Prenatal detection of rubella-specific IgM in fetal sera

Serum specimens were obtained by fetoscopy at 19-25 weeks' gestation from four fetuses whose mothers had had confirmed rubella earlier in pregnancy. They were tested for rubella-specific IgM by antibody capture radioimmunoassay. No specific IgM was detected in one fetus and a healthy infant was delivered at term. Specific IgM was detected in the other three fetuses. In one case the level was low (1 unit) and this pregnancy went to term resulting in a neonate with clinical and laboratory evidence of congenital rubella infection. The remaining two fetuses had 2.8 and 2.4 units of specific IgM and the pregnancies were terminated. Blood obtained from these two fetuses after abortion showed levels of 5.4 and 2.9 units respectively. No specific IgM was detected in sera from eleven other fetuses aborted because of maternal rubella but five of these cases were terminated before 19 weeks and in five the interval between rash and abortion was three weeks or less. The results show that the human fetus can produce detectable specific IgM antibody by 19-20 weeks' gestation after exposure to rubella several weeks earlier. However, a larger study is required to define the reliability of fetoscopic blood sampling for the diagnosis of intrauterine infection.

BK virus specific IgM responses in cord sera, young children and healthy adults detected by RIA

An IgM capture solid-phase radioimmunoassay (MACRIA) for BK virus (BKV) specific IgM is described. This test was found to be more sensitive in detecting BKV specific IgM than both haemagglutination inhibition and immune electron microscopy with serum fractions from sucrose density gradients. The use of this specific assay allowed large numbers of sera to be examined with ease so that the distribution of BKV specific IgM in different populations could be studied more fully. BKV specific IgM was detected in 11/300 sera from London blood donors, in 24/114 sera from children aged between 2 and 11 years admitted to a paediatric unit and 14/79 sera taken from children aged between 2 and 5 years for the investigation of anti-streptolysin 0 titres. BKV specific IgM was not detected in 404 cord sera examined to investigate the transplacental transmission of BK virus.

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.

An outbreak of erythema infectiosum associated with human parvovirus infection

Erythema infectiosum (EI) or fifth disease is a mild, acute exanthematous disease, occurring mainly among children, for which a causative virus has long been sought. In May 1983 an outbreak of exanthematous illness was reported in a primary school in North London. Children attending the school were investigated by questionnaire and 162 (43.9%) reported an illness with the features of EI. In each of 36 cases investigated virologically the illness was associated with parvovirus infection. Moreover, pre-existing antibody to parvovirus was correlated with protection from EI in 16 of 17 close family contacts of cases. We propose therefore that EI is the common manifestation of infection with the human parvovirus.

The immunoglobulin M response to rubella vaccine in young adult women

Rubella vaccination histories were taken from 333 young women working in the head office of a retail organization: 29% said they had had vaccine and 47% said they had not. The remainder did not know. Forty-six per cent of those less than or equal to 25 years old (who should have been offered vaccine at school), and 6% of those greater than 25 years old, said they had been vaccinated. When screened for immunity to rubella by radial haemolysis (RH) 3% had a low level of antibody (less than 15 i.u./ml) and 11% had no antibody. After immunization with Cendevax the specific rubella IgM response was measured by an IgM antibody capture radioimmunassay (MACRIA). It was only detectable in the group without RH antibody, and was present in 26/31 of them. The IgM response to Cendevax was strongest in specimens taken 20-39 days after immunization, but in 10 out of 11 cases tested was still present at around 71 days. The specific IgM responses to Cendevax were very similar to those in women given Almevax in an earlier study, when measured in parallel tests. Taking both vaccines together, specific IgM was present in 35 out of 36 vaccinees without pre-existing antibody tested between 40 and 77 days post-immunization. Detection of specific IgM by MACRIA would therefore be an effective means of determining susceptibility retrospectively in rubella vaccinees found to be pregnant.

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.

A comparison of Rubazyme-M and MACRIA for the detection of rubella-specific IgM

One-hundred and eighty-six carefully selected sera were tested for rubella-specific IgM by Rubazyme-M (Abbott Diagnostics) and an M-antibody capture radioimmunoassay (MACRIA). Eleven of these sera were from cases of infectious mononucleosis, six of which gave positive results in MACRIA, while one gave a positive result in Rubazyme-M. Of the remaining 175 sera, 158 gave concordant results whilst 17 sera gave discordant results; these 17 were also tested by serum fractionation. Problems were encountered with all assay systems used. It is therefore recommended that the results of all tests for rubella-specific IgM should be interpreted with caution.

A comparison of enzyme-immunoassay and radioimmunoassay for detection of hepatitis A virus and antibodies against hepatitis A virus

A direct comparison has been made of tracers labelled with an enzyme and with 125I in solid phase enzyme-immunoassay (EIA) and solid phase radioimmunoassay (RIA) for the detection of hepatitis A virus (HAV) antigen and antibodies to HAV. By comparing the binding capacity of peroxidase-labelled anti-HAV-IgG and anti-HAV-F(ab)2 fragments tracers, anti-HAV-IgG was found to have a higher binding capacity than anti-HAV-F(ab)2 fragments in both EIA and RIA. For EIA 16.25-fold more anti-HAV-IgG was needed for one test probe compared to RIA and 32.5-fold more anti-HAV-F(ab)2 fragments. For the detection of HAV antigen from stool preparations and IgG and IgM antibodies against HAV, there were only minor quantitative differences in titre. EIA was as sensitive as RIA.