Visual reading of enzyme immunofluorescence assays for human cytomegalovirus antibodies

Enzyme immunoassay for detection of human immunodeficiency virus antigens in cell cultures

A sensitive and specific avidin-biotin enzyme immunoassay that uses immunoreagents from naturally infected individuals was formulated for the detection of human immunodeficiency virus (HIV) antigens. A total of 500 cell culture samples from 111 cultures were tested in this assay and in a reverse transcriptase (RT) assay. Of 353 samples that were positive in the immunoassay, 174 were positive and 179 were negative in the RT assay. The specificity of the immunoassay results was supported by the failure of samples to react with nonimmune serum, by the ability of an anti-HIV type 1 monoclonal antibody to block the reactivity of selected samples, and by the appearance of RT activity in samples drawn from some cultures after a longer period of cultivation. HIV antigens were detected in 174 of 176 RT-positive samples (sensitivity, 98.9%). A comparison of the kinetics of antigen production and RT activity revealed that detectable antigen levels frequently preceded the appearance of RT activity. Thus, 50% of virus-containing cultures were identified within 9 days by immunoassay compared with 14 days by RT assay. In addition, RT activity was often detected intermittently in cultures sampled on several days, whereas antigen levels did not decline after initial appearance. Enzyme immunoassays for HIV antigen detection that use easily obtained reagents and simple technologies could facilitate laboratory and clinical research which requires cultivation of viruses.

Detection of IgM antibodies against Chlamydia trachomatis by enzyme linked fluorescence immunoassay

A simple, sensitive enzyme linked fluorescence immunoassay has been developed to detect IgM antibodies against Chlamydia trachomatis. Reticulate bodies and elementary bodies from C trachomatis L2/434 Bu strain were isolated and used as antigens in the assay. Of 113 serum samples obtained from infants with pneumonia, 27 (23.9%) had IgM antibodies to C trachomatis L2 reticulate bodies and nine (8.0%) had IgM antibodies to C trachomatis L2 elementary bodies (titre greater than or equal to 1/500). Specific IgM antibodies were not detected in 20 control serum samples obtained from healthy adults and children. The possible use of enzyme linked fluorescence assay to determine IgM antibodies in the serodiagnosis of C trachomatis infection is discussed.

Comparison of enzyme linked immunosorbent assay and enzyme linked fluorescence immunoassay for detection of antibodies against Chlamydia trachomatis

An enzyme linked fluorescence immunoassay (ELFA) has been evaluated for the detection of antibodies against Chlamydia trachomatis. Reticulate bodies and elementary bodies from C trachomatis L2/434 strain were used as antigens. An enzyme linked immunosorbent assay (ELISA) has also been evaluated using the same antigens. Results obtained by ELISA and ELFA for human sera with these two antigens were compared with each other and with the results obtained by a micro-immunofluorescence (micro-IF) test. Serum IgG antibodies against C trachomatis L2 reticulate bodies and elementary bodies were found in 32 (20.0%) and 11 (6.9%), respectively, of 160 serum samples from pregnant women by the micro-IF test (titre greater than or equal to 1/32). All of these 32 pregnant women had IgG antibodies to C trachomatis reticulate bodies (titre greater than or equal to 1/100), whereas 20 (12.5%) had IgG antibodies to elementary bodies in the ELISA. On the other hand, 25 (15.6%) and 19 (11.9%) of them had IgG antibodies to C trachomatis L2 reticulate bodies and elementary bodies, respectively, by the ELFA (titre greater than or equal to 1/500).

Comparison of enzyme-linked immunosorbent assay with enzyme-linked fluorescence assay with automated readers for detection of rubella virus antibody and herpes simplex virus

The enzyme-linked immunosorbent assay (ELISA) was compared with the enzyme-linked fluorescence assay (ELFA) for the detection of rubella antibody and herpes simplex virus antigen. Test parameters, specimens, antigen or antibody, and conjugates for the two types of assays were identical except that p-nitrophenyl phosphate was used as the substrate for the ELISA and 4-methylumbelliferyl phosphate was used as the substrate for ELFA. Automated readers were used for both assays. Antibody titers and sensitivity of antigen detection were quite similar for ELISA and ELFA. ELFA for rubella antibody, however, could be conducted with less antigen or shorter substrate incubation time (5 min for ELFA versus 30 min for ELISA). For herpes simplex virus antigen detection, ELFA could also be read after a shorter substrate incubation time (15 min for ELFA versus 30 min for ELISA). Clear polystyrene microtiter plates routinely used for ELISA could be used for ELFA, but clear polyvinyl chloride plates had high background fluorescence. Black polystyrene and polyvinyl chloride plates gave lower background fluorescence than did clear plates. ELFA is of particular value as a substitute for ELISAs in which long substrate incubations are required or antigens of only low titer are available.

Varicella-zoster viral glycoproteins analyzed with monoclonal antibodies

Monoclonal antibodies to varicella-zoster virus were used to study viral glycoproteins by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Based on the viral glycoproteins immunoprecipitated, the five monoclonal antibodies fell into three groups. Two antibodies, 4B7 and 8G9 (group 1), immunoprecipitated a single glycoprotein of molecular weight (MW) 118,000 (118K glycoprotein) and had high neutralizing activity in the absence of complement. One antibody, 3C7 (group 2), which lacked neutralizing activity, immunoprecipitated two glycoproteins of MWs 120,000 and 118,000 and a glycoprotein giving a diffuse band in the region of 64,000 to 65,000. Pulse-chase experiments and experiments with monensin as an inhibitor of glycosylation suggested that the 120K polypeptide was derived by glycosylation of the 118K polypeptide and that a 43K antigen was processed into the 64 to 65K glycoprotein. Two antibodies, 3G8 and 4E6 (group 3), both had neutralizing activity only in the presence of complement, and both immunoprecipitated at least five polypeptides, with MWs ranging from 50,000 to 90,000. Antibody 3G8 was isotype immunoglobulin G2b (IgG2b), and its immunoprecipitating activity was stronger than that of 4E6, which was isotype IgG1. Pulse-chase experiments with antibody 3G8 showed that lower-MW glycopeptides chased into three polypeptides of MWs 90,000, 80,000, and 60,000 by 24 h. Immunoprecipitation experiments with antibody 3G8 on infected cells treated with glycosylation inhibitors 2-deoxyglucose, monensin, and tunicamycin, suggested that a prominent, early-appearing 70K polypeptide may have been processed into the glycoproteins of higher MWs and that the 60K polypeptide may have been derived by glycosylation of polypeptides of lower MWs.

Coxsackievirus B3 persistence and myocarditis in NFR nu/nu and +/nu mice

NFR nude (nu/nu) and euthymic (+/nu) littermates were infected with coxsackievirus B3 (CBV-3) and assayed for virus persistence in the heart, pancreas and spleen, for development of myocarditis and for antibody production. The virus grew to higher titer and persisted longer in hearts of nu/nu mice. In both types of mice there was comparable myocarditis with a mononuclear cell inflammatory response, and there was some evidence of chronic lesions for up to 21 days in +/nu and 28 days in nu/nu mice. Antibody of the IgM class was present at 7 days in both strains of mice. Thereafter, +/nu mice produced high titers of virus-specific IgG antibody, while nu/nu mice produced little or no viral IgG antibody. The persistence of virus for up to 28 days in NFR nude mice is longer than has been reported previously, and offers an opportunity for further study of the role of T-cells in virus persistence and myocarditis.

Antibody class capture assays for varicella-zoster virus

Pooled monoclonal antibodies to varicella-zoster virus (VZV) were used as "detector" antibodies in a four-phase enzyme immunofluorescence assay for determination of immunoglobulin M (IgM), IgA, and IgG antibodies to VZV. Polyclonal antisera specific for heavy chains of human IgM, IgA, and IgG were employed as "capture" antibodies on the solid phase. The antibody class capture assay (ACCA) for VZV IgM antibody detected high titers of virus-specific IgM in all patients with varicella and in 5 of 10 zoster patients. VZV IgM antibody was not detected in patients with primary herpes simplex virus infections or in other individuals without active VZV infection, with one exception, a patient with encephalitis who had other serological findings compatible with a reactivated VZV infection. VZV-specific IgA and IgG antibody titers demonstrable by ACCA were compared with those measured by solid-phase indirect enzyme immunofluorescence assay (EIFA). VZV IgA antibody titers detected in patients with varicella and zoster were variable and could not be considered to be reliable markers of active VZV infection. IgA antibody titers detected by ACCA tended to be higher than those demonstrated by solid-phase indirect EIFA in varicella and zoster patients. VZV IgG antibody titers detected by ACCA in patients with varicella, and to a lesser extent in zoster patients, were as high as or higher than those demonstrated by solid-phase indirect EIFA. However, ACCA was totally insensitive in detecting VZV IgG antibody in individuals with past infections with VZV and would not be a suitable approach for determination of immunity status to VZV.

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

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

Production of monoclonal antibodies to human IgM for assay of viral IgM antibodies

Monoclonal antibodies to human IgM were produced by fusing the Sp 2/0-Ag 14 line of mouse myeloma cells with spleen cells from BALB/c mice immunized with purified human IgM. From 6 clones which secreted antibody to human IgM, the one which produced the highest levels of antibody and grew relatively rapidly was selected for expansion and production of immune reagents for viral IgM antibody assays. Mouse ascitic fluids produced with this clone of cells had antibody titers for human IgM of 1 X 10(-10) by indirect enzyme immunofluorescence assay (EIFA). The monoclonal antibodies were found to belong to subclass 1 of murine IgG, and their specificity was shown to be directed against the Fab portion of the mu chain of human IgM. Antibodies from murine ascitic fluid conjugated with horseradish peroxidase were shown to be suitable for assay of measles IgM antibody by indirect immunoperoxidase staining. Antibodies conjugated with alkaline phosphatase could be used in an indirect EIFA for determination of measles IgM antibodies; use of monoclonal conjugates in this system eliminated the nonspecific activity observed in tests utilizing polyclonal anti-mu reagents. Further, the monoclonal antibodies were highly satisfactory for use in a 'capture' system for viral IgM antibody assays. The availability of monoclonal antibodies to human IgM overcomes problems with specificity, consistency and supply which have previously hindered development and standardization of viral IgM antibody assays.

Serological reactivity of some monoclonal antibodies to varicella-zoster virus

Monoclonal antibodies to varicella-zoster virus, free from host cell reactivity, were produced by cell fusion technics. Antibodies from four different clones showed diverse activities in neutralization immunofluorescence and complement fixation assays. The antibodies provide useful reagents for viral diagnosis and viral antigenic characterization.

Comparison of fluorescent and colorigenic substrates for enzyme immunoassays

A variety of substrates can be employed in enzyme immunoassays (EIAs) for the measurement of enzyme-labeled immunoreactants. We compared the sensitivities of a fluorescent and a colorigenic substrate in an EIA system for the measurement of Haemophilus influenza purified polyribose phosphate. After a 10-min substrate incubation, the EIA in which the fluorescent substrate was used could detect 10 pg of polyribose phosphate per ml, whereas the EIA in which the colorigenic substrate was used required the addition of 640 pg of polyribose phosphate per ml to generate a positive reading. However, the use of longer substrate incubation periods led to an increase in sensitivity of the colorigenic EIA. After an incubation period of 240 min, the sensitivity was equal to that of the EIA in which the fluorescent substrate was used. These results suggest that the ultimate limit of sensitivity of EIA systems is determined by the nature of the antigen-antibody reactions. However, the use of high-energy substrates in EIA systems can allow for the attainment of maximal sensitivity after short enzyme-substrate incubation periods.

Detection of La Crosse arbovirus antigen in mosquito pools: application of chromogenic and fluorogenic enzyme immunoassay systems

An enzyme immunoassay producing either a chromogenic or fluorogenic end product was developed and evaluated for detecting La Crosse viral antigen within mosquito pools. The enzyme immunoassay was found to be sensitive, detecting one infected mosquito within a pool of 100 mosquitoes, and specific, distinguishing between closely related California group viruses. Assays were completed within 5 h after the addition of test samples. La Crosse viral antigen could be readily detected in mosquito pools after seven freeze-thaw cycles.

Humoral immune response to virions and dense bodies of human cytomegalovirus determined by enzyme immunofluorescence assay

An enzyme immunoassay utilizing a fluorogenic substrate (EIFA) was employed to compare humoral antibody responses to purified virion and dense body antigens in human cytomegalovirus (CMV) infections. Results of these antibody assays were also compared to those obtained by plaque reduction neutralization and complement fixation (CF). In adults with CMV infections diagnosed by a significant rise in CF antibody titer, there was also a vigorous antibody response to the virion and dense body antigens. There was better correlation between antibody levels to the virion and dense body antigens than between antibody levels detected by other combinations of tests. Antibody responses to the virion and dense body antigens were similar, but not identical, suggesting that although the two structures share major antigens, they may also possess unique antigens to which the host can mount independent antibody responses. All individuals with CMV neutralizing antibody also had virion and dense body antibodies, but there was poor correlation between neutralization titers and those detected by EIFA, perhaps reflecting greater strain specificity of the neutralization test. Some individuals with serological diagnoses of Mycoplasma pneumoniae or influenza A infection showed fourfold or greater antibody titer rises to CMV in two or more assays, suggesting reactivation of latent CMV in these infections.