Enzyme immunoassays for measurement of cytomegalovirus immunoglobulin M antibody

Low total IgM values and high cytomegalovirus loads in the blood of newborns with symptomatic congenital cytomegalovirus infection

AIMS

Neurological outcomes differ considerably between symptomatic and asymptomatic infants with congenital cytomegalovirus (CMV) infection. Our objective was to characterize laboratory markers in symptomatic newborns in comparison with asymptomatic newborns with congenital CMV infection.

METHODS

Ten newborns with symptomatic and 13 newborns with asymptomatic congenital CMV infection were included in this 3-year prospective cohort study. Total immunoglobulin M (IgM), CMV-IgM, CMV antigenemia, and CMV-DNA in blood and urine were measured and their positive rates and quantitative values compared between the symptomatic and asymptomatic groups.

RESULTS

Fifty percent of newborns in the symptomatic group were positive based on total IgM; this was significantly lower than in the asymptomatic group (100%). Quantitative total IgM values were significantly lower, and there were significantly more copies of CMV-DNA in the blood of symptomatic newborns than in asymptomatic newborns (median values for total IgM: 14 vs. 43 mg/dL and blood CMV-DNA: 3.2×102 vs. 3.5×101 copies/106 white blood cells). CMV-IgM, CMV antigenemia, and urine CMV-DNA did not differ significantly between groups.

CONCLUSION

Low total IgM values and high blood CMV loads were associated with the presence of symptoms in newborns with congenital CMV infection.

Detection of IgM responses to bovine respiratory syncytial virus by indirect ELISA following experimental infection and reinfection of calves: abolition of false positive and false negative results by pre-treatment of sera with protein-G agarose

The IgM responses in three panels of sera generated by infection and reinfection of calves with bovine respiratory syncytial virus (BRSV) were measured by indirect ELISA (I-ELISA). The effect of depleting serum IgG by pre-treatment with protein G agarose (PGA) was evaluated. Following primary infection a weak IgM response was detected in the untreated sera of 3 out of 4 calves with maternally derived antibody (MDA). Both the magnitude and duration of the specific IgM responses in these calves were increased by pre-treatment with PGA. In addition, the fourth infected calf tested gave a single positive IgM result following PGA treatment. Transient or persistent IgM responses which were abolished by pre-treatment of sera with PGA were detected in 4/8 calves following reinfection. These were considered to be false positive results, consistent with the influence of IgM rheumatoid factor (IgM-RF). One of these calves and two additional calves showed transient increases in IgM which were resistant to PGA treatment. These were considered to represent specific IgM responses to reinfection. The results indicate the ability of PGA treatment to eliminate both false positive and false negative results and emphasise the necessity for controlling the influence of IgM-RF in IgM-specific indirect ELISAs.

TORCH syndrome

The original TORCH complex described clinically similar congenital infections caused by Toxoplasma gondii, rubella virus, cytomegalovirus, and herpes simplex virus, types 1 and 2. Cutaneous manifestations, including petechiae, purpura, jaundice, and dermal erythropoiesis, are commonly seen in toxoplasmosis, rubella, and cytomegalovirus infections. In herpes simplex virus infections, 80% of symptomatic infants show single or grouped cutaneous vesicles, oral ulcers, or conjunctivitis. Extracutaneous signs and symptoms are variable and can be severe. Significant clinical signs in congenital toxoplasmosis include diffuse intracerebral calcification, chorioretinitis, and microcephaly; congenital rubella can result in deafness, congenital heart disease, retinopathy, and brain calcification. Cytomegalic inclusion disease can include hepatomegaly, splenomegaly, paraventricular calcification, and intrauterine growth retardation. Localized or disseminated congenital herpes virus infection often involves the central nervous system and the eye. Diagnosis is confirmed by culture and identification of species-specific immunoglobulin M within the first 2 weeks of life. Histological examination contributes to the diagnosis in herpes simplex virus infection. Treatment for toxoplasmosis includes pyrimethamine with sulfadiazine or trisulfapyrimidine; congenital herpes simplex virus infection is treated with acyclovir. No specific therapy for congenital rubella or cytomegalovirus infections has been established, and so treatment is primarily supportive.

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.

An enzyme immunoassay to detect specific antibodies to protein and lipopolysaccharide antigens of Chlamydia trachomatis

We have developed an enzyme immunoassay to measure antibodies to the proteins and lipopolysaccharide (LPS) of Chlamydia trachomatis. Antibodies to proteins could be differentiated from antibodies to lipopolysaccharide (LPS) by treatment of the antigen with periodate or Triton X-100. Some important parameters of the oxidation by periodate were studied by comparing the response of several monoclonal antibodies. Four types of response could be observed: type I, a reduced response after mild or strong oxidation; type II, a normal response after mild oxidation, but reduced after strong oxidation; type III, not affected; type IV, an increased response after oxidation. Treatment with Triton X-100 had the same effect as mild oxidation and confirmed the response types I, III, and IV. Treatment of antigen with periodate reduced the IgG response measured in sera from patients with evidence of Chlamydia psittaci infection.

A review of enzyme immunoassay for detection of antibody to Brucella abortus in cattle

Enzyme immunoassay has gained wide acceptance for serological diagnosis of bovine brucellosis because of its ability to detect antibody of all isotypes unlike the conventional tests. The indirect enzyme immunoassay, however, presents several parameters that require careful analysis. These parameters include the choice of antigen and antiglobulin-enzyme conjugate reagents for use in the assay, dealing with the large amount of data the semi-automatic or automatic assay can generate and the inter- and intralaboratory standardization and quality control. This review considers the various methods described in the literature and, briefly, how some of the problems have been overcome or how they might be dealt with.

Enzyme-linked immunosorbent assay detection of immunoglobulins G and M to Venezuelan equine encephalomyelitis virus in vaccinated and naturally infected humans

Enzyme-linked immunosorbent assays (ELISAs) were developed for detection of immunoglobulin G (IgG) and IgM antibodies to Venezuelan equine encephalomyelitis (VEE) virus in vaccinated and naturally infected humans. A total of 441 sera found negative for VEE antibodies by plaque reduction neutralization were examined by IgG ELISA and gave a 1.0% false-positive rate; no false-positives were found in the IgM ELISA. Sera with neutralizing antibody to western or eastern equine encephalomyelitis virus did not react with VEE antigen in the IgG ELISA. Sensitivity of the IgG ELISA was determined by testing 100 coded pre- and postvaccination human sera. Sixty-two were positive by ELISA; 58 of these 62 were also positive by neutralization tests, and 38 were negative by both tests. No neutralization-positive, ELISA-negative sera were found. Comparison of titers obtained by ELISA and neutralization tests indicated that 88% varied randomly by a fourfold dilution factor or less, while 61% were identical or varied only twofold. In sera obtained sequentially from 10 vaccinees and 5 naturally infected patients, both IgG and IgM antibodies appeared between 2 and 3 weeks after vaccination or onset of symptoms. The IgG and IgM antibody ELISAs described are rapid, specific, and sensitive indicators of VEE antibody status in vaccinated and naturally infected individuals.

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.

Evaluation of quaternary aminoethyl-Sephadex A50 column chromatography for detection of anti-cytomegalovirus immunoglobulin M

The sensitivity of an indirect fluorescent antibody (IFA) test (screening test) for the detection of antibodies to cytomegalovirus (CMV) was examined by using 128 serum specimens and quaternary aminoethyl (QAE)-Sephadex A50 column chromatography to separate IgM from IgG class antibodies. Of these 128 rheumatoid factor-negative serum samples, only 54 (42%) continued to produce fluorescence after the IgG was removed by the Sephadex column (yielding a theoretical 1:10 dilution) and the samples were retested for IgM (confirming test). Of the 54 specimens that were positive on both the screening and confirming IgM IFA assays, 53 (98%) had titers of 1:80 or more. Of the 74 sera that were negative on the confirming test, only 10 (14%) had titers of 1:80 on the initial screening test, and none was greater than 1:80. Immunoglobulin measurements of eight serum samples before and after column treatment indicated excellent IgG removal but poor IgM recovery (a mean loss of 85% of the total IgM). Comparison of the time needed to detect IgM in CMV culture-positive patients demonstrated an increase from 17.1 to 28.3 days (serum tested by IFA before and after column separation, respectively). Therefore, confirmation of anti-CMV IgM in serum specimens by QAE-Sephadex A50 column chromatography seems to be of low sensitivity.

An enzyme labelled nuclear antigen immunoassay for detection of cytomegalovirus IgM antibodies in human serum: specific and non-specific reactions

A mu-capture enzyme linked immunosorbent assay was developed for detection of IgM antibody to cytomegalovirus (CMV). Virus-specific IgM was detected using horseradish peroxidase labelled nuclear CMV antigen (CMV-ELA). False-positive reactions caused by Paul-Bunnell-Davidsohn (PBD) positive sera and antinuclear antibody (ANA) positive sera were identified in a combination assay employing enzyme labelled nuclear control antigen (CO-ELA) in parallel to the CMV-ELA. Four of five PBD positive and 30 of 31 ANA positive sera reactive with the CMV-ELA were identified as false positive reactions in the combined ELA-assay. The reactivity in PBD-positive sera could not be explained by antigenic cross reactivity between CMV and Epstein-Barr virus, and the results further suggested that different cell specified components of the CMV-ELA were responsible for the reactivity of PBD-positive as compared to ANA-positive sera. One of 314 healthy blood donors, 12 of 12 patients with primary CMV infection, and 11 of 15 patients with secondary CMV infection had detectable CMV IgM antibodies. Comparison of different CMV-ELAs revealed that pronounced differences in specificity as well as sensitivity may exist.

Comparison of Isolab Quik-Sep and Quik-Sep System II for separation of immunoglobulins G and M

Use of Quik-Sep System II (QSII) ion-exchange chromatography increased the detection of CMV-directed immunoglobulin M (IgM) compared to the prototype Quik-Sep System (QSI) (27 of 87 [31%] IgM-positive versus 20 of 87 [24%]). However, an increase in the number of false-positive rheumatoid factor-containing sera was found (15/52 [29%] versus 8/52 [15%]). Total immunoglobulin G (IgG) and IgM concentrations were higher in the QSII eluates compared to those from QSI, although total IgM recovery did not exceed 36% in either system.

Immunoglobulin M to cytomegalovirus in primary and reactivation infections in renal transplant recipients

Two commercially available enzyme immunoassays and one assembled in house were used to measure immunoglobulin M (IgM) antibody to cytomegalovirus (CMV) in a total of 220 serum specimens from 104 renal transplant recipients. All assays included a step in which interfering IgG antibody was removed or complexed. Concordance of results between pairs of assays ranged from 84 to 96%. All sera from patients with recent seroconversion (primary CMV infection) had measurable anti-CMV IgM. Among those already seropositive to CMV when transplanted, 26 to 55% had IgM antibody posttransplant, depending on the assay. This was observed regardless of the CMV serologic status of the kidney donor, indicating that reactivation of endogenous CMV, as well as reinfection, can induce this antibody in transplant recipients. Four cadaver donors known to transmit CMV to eight recipients did not have measurable IgM antibody to CMV.

Elimination of nonspecific cytomegalovirus immunoglobulin M activities in the enzyme-linked immunosorbent assay by using anti-human immunoglobulin G

Direct enzyme-linked immunosorbent assay methods offer several advantages in assessing past or recent exposure to cytomegalovirus (CMV) infection, but there persist many pitfalls in the use of these methods for determining specific immunoglobulin M (IgM). The efficiency of absorption of sera by IgG-coated latex beads, aggregated human IgG, or Staphylococcus aureus, i.e., for removing nonspecific CMV IgM activities, was evaluated in comparison with the effect of an anti-human IgG hyperimmune serum. Large routine series comprising serum samples from patients of various clinical groups and healthy individuals were examined. The CMV IgM-positive samples were at first treated with latex or aggregated IgG, but these absorptions left too many CMV IgM-positive individuals. S. aureus increased the nonspecific activity of some sera and, in other cases, removed or impaired specific IgM activities. The anti-IgG treatment caused the disappearance of nonspecific CMV IgM activities that had resisted the other treatments, whereas specific activities remained intact. Utilizing this method, only 1.03% of the routine series patients remained CMV IgM positive by the enzyme-linked immunosorbent assay, a figure in good agreement with a mean probability of CMV antibody acquisition of 0.33% for the population living in Belgium. On the other hand, in a series of patients who were investigated for serological response to several viruses, eight individuals displayed multiple IgM activities after anti-IgG treatment. In these cases, most IgM activities were found in patients who had IgG toward the related antigen for a long time before transient IgM was detected. This result implies that to assess a diagnosis of primary infection, it is necessary to examine serial specimens for IgG acquisition accompanying specific IgM.

Hemadsorption immunosorbent technique for the detection of dengue immunoglobulin M antibody

We developed a highly specific, sensitive, and economical hemadsorption immunosorbent technique for the detection of dengue-specific immunoglobulin M (IgM) antibody. The technique is based on the reaction of human sera with anti-human IgM immobilized onto a solid phase followed by the detection of dengue-specific IgM by the addition of a known quantity of dengue virus hemagglutinin and goose erythrocytes. Dengue-specific IgM-positive sera showed hemadsorption. IgM antibody specific for dengue virus was detected in 22 of 39 (56%) convalescent-phase sera from primary dengue infections and 8 of 10 (80%) convalescent-phase sera from secondary dengue infections. Additionally, 32 of 76 single sera from patients were positive for dengue IgM; these sera were previously uninterpretable by the hemagglutination inhibition test, as only a single serum specimen was available. No false-positive results were obtained with sera that were negative by the hemagglutination inhibition test for dengue virus. Crude dengue virus hemagglutinin preparations could be used without purification. Dengue-specific IgG did not interfere with the results, nor was there any cross-reactivity between dengue hemagglutinins and IgM specific for other viruses. Some cross-reactivity of the dengue-specific IgM was observed with Japanese encephalitis virus hemagglutinins, but this did not present any problems in the interpretation of results. This test is specific, inexpensive, highly reproducible, and simple to perform.

In situ hybridization for the detection of cytomegalovirus (CMV) infection. Application of biotinylated CMV-DNA probes on paraffin-embedded specimens

Five autopsy cases of cytomegalovirus (CMV) infections were studied. Conventional light microscopy disclosed characteristic cytopathic effects in lungs, kidneys, and brain. In one case, electron microscopy was carried out and revealed typical herpesvirus particles. In situ hybridization was done with biotin-labeled CMV-DNA probes and an avidin-alkaline phosphatase detection system. 4/5 cases were observed to contain hybridizing cells in different organs. Intensity of hybridization was related to the severity of CMV infection, roughly estimated by counting cytomegalic cells. In addition to cytomegalic cells, a high number of normal-looking epithelial and mesenchymal cell types were positive. These latter cells showed nuclear hybridizations in contrast to cytomegalic cells which hybridized both within the nuclei and the cell bodies. This modified in situ hybridization procedure is a rapid and valuable tool for the detection and final demonstration of virus infection, and will be of particular help for the examination of paraffin-embedded specimens.

Detection of Ross River virus immunoglobulin M antibodies by enzyme-linked immunosorbent assay using antibody class capture and comparison with other methods

An enzyme-linked immunosorbent assay based on antibody class capture was developed for the detection of Ross River virus-specific immunoglobulin M antibodies (RRV IgM). The assay was specific, reproducible and precise. When compared with conventional tests for the detection of RRV IgM, such as hemagglutination inhibition following sucrose density gradient centrifugation and indirect enzyme-linked immunosorbent assay, the class capture assay was more sensitive. In 186 sera which were collected from 39 patients with RRV infection over a period of 1-4 yr from onset of initial symptoms, RRV IgM persisted for at least 1-2 yr. Sera were tested both at a single dilution from which the results were expressed as a binding index and in a dilution series in which they were expressed as an antibody titre. Binding index values gave better discrimination between sera collected during acute and later phases of the disease and may be of greater value than antibody titres in the diagnosis of RRV infection.

Determination of specific cytomegalovirus IgM antibodies using infected air dried cells and isolated nuclei by immunoperoxidase assay

A simple immunoperoxidase assay (IPA), adapted for detection of serum IgM antibodies to cytomegalovirus (CMV) is described. The antigen consisted of CMV infected human embryonic fibroblasts or isolated nuclei. The sera were absorbed with aggregated gamma-globulins prior to testing. Rabbit anti-human IgM peroxidase conjugate was used to detect IgM bound to viral antigen. In parallel the enzyme linked immunosorbent assay (ELISA) technique was used to determine IgG and IgM antibodies to CMV, respectively. All patients with acute CMV infections who were tested had CMV-specific IgM antibodies by IPA, both whole cell and nuclei antigen. The maximal IgM titers were higher by ELISA than by IPA but in 3 of the CMV patients IgM was detected earlier by IPA (with both types of antigens) than by ELISA. In 3 of 5 transplant patients with recurrent CMV infection IgM was demonstrated by immunoperoxidase techniques, while by ELISA IgM was demonstrated in only 2 of them. No cross reactivity with other herpes viruses was observed. The described IPA is simple, rapid and has the potential for widespread use in routine laboratories.

Detection of immunoglobulin M and G antibodies against cytomegalovirus early and late antigens by enzyme-linked immunosorbent assay

A sensitive and reproducible enzyme-linked immunosorbent assay (ELISA) is described for the detection of immunoglobulin M and antibodies with specifity for human cytomegalovirus (CMV) early (CMV-EA) and late (CMV-LA) antigens. The emphasis is on the production of high-quality CMV antigens, CMV-EA and CMV-LA separately, and conditions for their application in the ELISA. The induction of CMV-EA and -LA in infected cell extracts was studied in detail by using human sera with defined antibody specificity for CMV-EA and CMV-LA. This resulted in the development of a simple whole cell extraction procedure that provided a high yield of CMV antigens with reproducible antigen quality. The antigens were specific for the detection of anti-CMV antibodies. The influence of autoantibodies on the determination of CMV-specific antibodies was investigated. Parallel analysis of 322 human sera by indirect immunofluorescence and ELISA showed a high correlation between both assays (r = 0.9674 for CMV-EA and 0.9362 for CMV-LA). Antibody titers determined by ELISA were equal to (for CMV-EA) or slightly higher (for CMV-LA) that those determined by immunofluorescence but significantly higher (20- to 5,120-fold) than those determined by complement fixation. From 191 sera positive by ELISA (titer greater than or equal to 40) 4 (2.1%) were negative by immunofluorescence (titer less than 40), and from 61 ELISA-positive sera 12 (19.6%) were negative (titer less than 8) when tested by complement fixation. Consequently, ELISA for CMV may prove to be more reliable for the selection of CMV-seronegative blood donors than these other methods. The use of high-quality antigens allows more economic handling of large-scale serum determinations. Possibilities for further automation are discussed.

Immunity to human cytomegalovirus measured and compared by complement fixation, indirect fluorescent-antibody, indirect hemagglutination, and enzyme-linked immunosorbent assays

The complement fixation test is currently the test employed most frequently to determine the presence of antibody to human cytomegalovirus. Several other techniques have been adapted for this purpose. A comparison of cytomegalovirus antibody titers was made between the complement fixation test, a commercially available enzyme-linked immunosorbent assay, an indirect immunofluorescent technique, and a modified indirect hemagglutination test. Forty-three serum samples were tested for antibodies by each of the above procedures. The enzyme-linked immunosorbent, immunofluorescent, and indirect hemagglutination assays were in close agreement on all samples tested; the titers obtained with these methods were all equal to or greater than the complement fixation titer for 38 of the 41 samples (92.6%). Two samples were anticomplementary in the complement fixation test but gave readable results in the other tests. The complement fixation test was the least sensitive of the procedures examined. The commercial enzyme-linked immunosorbent assay system was the most practical method and offered the highest degree of sensitivity in detecting antibodies to cytomegalovirus.

Detection of viral antigens, particles, and early antibodies in diagnosis

Immunoassays for the detection of viral antigens in clinical specimens and virus-specific IgM responses in serum have shortened the time required to make a laboratory diagnosis of several infections. A range of antigen detection systems are available, varying in sensitivity, complexity, and expense, and each may have a role to play depending upon the laboratory setting. Technical advancements to eliminate false-positive results in solid-phase IgM assays have provided an awareness of very early IgM responses in diseases such as rubella, hepatitis A, and mumps. When clinical specimens contain large numbers of virus particles, a rapid diagnosis is easily made using electron microscopy. Detection of antigens, virus particles, and IgM responses is creating increased demands for viral diagnostic services in primary care settings. Other approaches using sensitive probes for viral nucleic acids or enzymes will also serve as viable laboratory techniques in the future.

Nonculture techniques using blood specimens for the diagnosis of infectious disease

Recent technological advances have increased the use of blood as a source for diagnosis of local and systemic infectious diseases. Traditionally, viable organisms may be cultured from the blood and others identified microscopically. The ability to detect microbial products by physicochemical, bioactivity, and antigenic techniques and the ability to detect specific immunoglobulin M (IgM) responses to infection improve our diagnostic capabilities but also present new problems in determining clinical relevance. The diagnostic use and reproducibility of new tests should be verified by comparative clinical field testing before implementation.

Comparison of methods for quantitating antigen-specific immunoglobulin M antibody with a reverse enzyme-linked immunosorbent assay

We compared two methods for quantitating antigen-specific antibody by a reverse enzyme-linked immunosorbent assay. In the serial-dilution method, the result was determined to be the highest dilution of a serum yielding an absorbance above an established threshold. In the single-dilution method, the result was determined by comparing the absorbance yielded by the test serum at a standard dilution to that yielded by positive and negative reference sera at the same dilution. The results in the single-dilution method reflected the antigen-specific immunoglobulin M antibody activity as a proportion of total immunoglobulin M antibody in a serum, i.e., the immune load, whereas the results in the serial-dilution method reflected the absolute concentration of antigen-specific immunoglobulin M antibody activity. Compared with results in the serial-dilution method, results in the single-dilution method had considerably greater reproducibility on a day-to-day basis and under various test conditions. The single-dilution method was more useful in discriminating between sera from patients in an early stage of clinical infection due to Toxoplasma gondii and sera from patients in a later stage of infection.

Diagnosis of acute toxoplasmosis by an enzyme immunoassay for specific immunoglobulin m antibodies

A recently developed enzyme-linked immunosorbent assay for detection of immunoglobulin M (IgM) class antibodies to Toxoplasma gondii was evaluated with respect to specificity and sensitivity. By using an antibody capture principle and F(ab')2 conjugates, interference of rheumatoid factors was absent. No cross-reactions with anti-toxoplasma IgG occurred, and no interference with antinuclear antibodies was found. A large-scale study with about 1,500 clinical specimens revealed a 100% specificity. By testing 79 sera from patients with acute-phase acquired toxoplasmosis, sensitivity was found to be 97%. In routine clinical practice, the IgM-enzyme-linked immunosorbent assay proved to be a more sensitive tool for diagnosis than the immunofluorescent-antibody test. The course of IgM-enzyme-linked immunosorbent assay antibodies in acute patients was studied; IgM reached peak levels within 1 month after onset of illness, and could be demonstrated up to an average of 8 months after onset.

The detection of antibodies to cytomegalovirus in the sera of renal transplant patients by an IgM antibody capture assay

An IgM antibody capture assay for detection of cytomegalovirus (CMV) IgM antibody (MACRIA) was developed. It was shown to be of similar sensitivity to the indirect immunofluorescence test but has the advantage that rheumatoid factor does not react in it and pretest fractionation of serum is not required. It does, however, give false results with some Paul Bunnell-positive sera. The assay was used to measure the IgM response in 28 renal transplant patients followed prospectively. Seven patients (100%) with primary infections and six of 13 (46%) patients with secondary infections developed IgM by MACRIA. Nine of 13 (69%) patients with CMV IgM-positive sera had symptoms other than pyrexia associated with CMV infections, while only one of seven (14%) IgM-negative infections were symptomatic. Four of seven irreversible rejection episodes were associated with CMV IgM. The possible significance of CMV IgM production is discussed.

Capture immunoglobulin M system for rapid diagnosis of La Crosse (California encephalitis) virus infections

A capture immunoglobulin M (IgM) enzyme immunoassay was developed to diagnose La Crosse virus infections by the detection of specific IgM in acutephase serum specimens. IgM was detected by the capture IgM system in the serum of 24 of 29 (83%) of the patients studied. In comparison, IgM was detected in 19 of 29 (66%) of the patients by an indirect immunofluorescence technique. Specific IgM was detected in 83% (20 of 24) of patient serum specimens by day 3 after the onset of clinical symptoms.

Cytomegalovirus antibody in cerebrospinal fluid of schizophrenic patients detected by enzyme immunoassay

By means of enzyme immunoassay techniques to detect the presence of antibody to cytomegalovirus, the cerebrospinal fluid of 178 patients with schizophrenia, 17 patients with bipolar disorders, and 11 other psychiatric patients was compared with that of 79 neurological patients and 41 normal control subjects. The cerebrospinal fluid of 20 of the schizophrenic patients and 3 of the patients with bipolar disorders showed significant increases in immunoglobulin M antibody to cytomegalovirus; no difference was found in patients on or off psychotropic medications.