Selective reactivity of antibodies to human immunoglobulins G, M, and A with rubella virus proteins

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

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

Molecular biology of rubella virus

This chapter summarizes the present medical significance of rubella virus. Rubella virus infection is systemic in nature and the accompanying symptoms are generally benign, the most pronounced being a mild rash of short duration. The most common complication of rubella virus infection is transient joint involvement such as polyarthralgia and arthritis. The primary health impact of rubella virus is that it is a teratogenic agent. The vaccination strategy is aimed at elimination of rubella and includes both universal vaccination of infants at 15 months of age with the trivalent measles, mumps, rubella (MMR) vaccine and specific targeting with the rubella vaccine of seronegative women planning pregnancy and seronegative adults who could come in contact with women of childbearing age, although it is recommended that any individual over the age of 12 months without evidence of natural infection or vaccination be vaccinated. Medically, the current challenge posed by rubella virus is to achieve complete vaccination coverage to prevent resurgences.

Detection of rubella virus-specific immunoglobulin G (IgG), IgM, and IgA antibodies by immunoblot assays

Immunoblot (IB) assays were developed for detection of rubella virus (RV)-specific immunoglobulin G (IgG), IgM, and IgA antibodies in human serum following natural infection or immunization. IB assays performed under nonreducing conditions were compared with those performed under reducing conditions and with immunoprecipitation assays. Significant loss of antigenicity (greater than 90%) of RV E1 and E2 proteins was observed when IB assays were performed in the presence of 2-mercaptoethanol as compared with assays under nonreducing conditions. In contrast, the antigenicity of RV capsid protein was not influenced by reducing agents. Sensitivity of IB for RV-specific IgG antibodies was determined to be 0.01 IU/ml under nonreducing conditions. In the determination of RV-specific IgM and IgA antibodies by IB, pretreatment of serum with protein G to remove competing high-affinity RV-specific IgG or rheumatoid factor significantly improved assay sensitivity. IB assays were observed to be superior to immunoprecipitation assays in their ability to better define the specificities of RV-specific antibodies and to detect antibodies of all immunoglobulin classes. However, the conformational sensitivity of RV protein antigenicity should be an important consideration in the interpretation of RV-specific antibodies by IB assays.

Diagnostic potential of baculovirus-expressed rubella virus envelope proteins

The envelope glycoproteins E1 and E2 of rubella virus were abundantly expressed in Spodoptera frugiperda Sf9 insect cells by using a baculovirus expression vector. The recombinant protein products were purified by immunoaffinity chromatography and characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, immunoblotting, and enzyme immunoassay (EIA). The purified recombinant antigen consisted of the envelope polypeptides, corresponding to the viral E1 and E2 proteins, and a polyprotein precursor (molecular mass, 90 to 95 kDa). The antigen was reactive with human convalescent-phase sera in immunoblot analysis, and the reactivity correlated well (r = 0.861) with that of a whole-virus antigen when tested by EIA by using a total of 106 rubella virus immunoglobulin G-positive and -negative serum specimens. When the sera from patients with recent rubella virus infection were tested with the recombinant glycoproteins by EIA, the correlation was not as close (r = 0.690). However, all of the 26 serum specimens were reactive with the recombinant antigen. The results demonstrate that these bioengineered antigens have a potential for use in routine diagnostic assays of rubella virus immunity and recent infection.

Sequential serological studies of homosexual men with and without HIV infection. Epstein-Barr virus activation preceding and following HIV seroconversion

Viral cofactors may be important in the pathogenesis of HIV infection and the development of AIDS, but their role is still imperfectly understood. Sequential serological studies were performed in a cohort of 100 homosexual men and 70 matched healthy controls over a mean period of 4 years. Of the patients, 18 were found to be HIV+ on admission to the study and 15 seroconverted to HIV+ during the follow up (seroconversion group). Serum antibodies of both IgG and IgA isotypes against Epstein-Barr virus (EBV) and cytomegalovirus (CMV) were determined. IgG antibodies indicate past infection, while a marked increase in IgG titre or a positive IgA titre were taken to indicate active infection or reactivated latent infection. EBV and CMV infections were about two to four times more prevalent in the homosexual men both HIV- and HIV+, compared with controls. Active infections were increased in the homosexual men and particularly in the HIV+ patients. The seroconversion group revealed activation of both EBV and CMV following HIV infection. When the antibody profile of seroconverting patients at the time preceding seroconversion was compared with a matched group of 39 homosexual men who remained HIV-, no change was found in CMV antibodies, but four out of 15 (26.6%) of the patients had high titres of anti-EBV IgA preceding seroconversion, as compared with only one out of 39 (2.6%) of HIV- homosexual men (P less than 0.05). This suggests a role for EBV reactivation in the pathogenesis of HIV infection in some patients.

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%.

Kinetics of isotype-specific humoral immunity in rubella vaccine-associated arthropathy

The present study documents the relationship between the development of rubella vaccine-associated arthropathy and isotype-specific rubella antibody responses in a prospectively studied population of 44 adult rubella hemagglutination inhibition (HAI) seronegative females undergoing rubella immunization. Rubella-specific IgM, IgG, and IgA antibody responses were evaluated prior to and at 1, 2, 3, 4, 5, 6, 12, and 24 weeks postvaccine. Detectable preimmunization rubella antibody of the IgG or IgA class was present using ELISA techniques in 6 of 6 individuals developing acute arthritis, 13 of 17 developing acute arthralgia, and in 15 of 21 with no joint manifestations postvaccine. Significantly elevated HAI IgM responses were noted 3 and 4 weeks postvaccine in the acute arthritis group but no significant differences were found in IgG and IgA rubella antibody levels postvaccine in relation to the presence or absence of joint manifestations at any time period postvaccine. The data support rubella reinfection as an important feature of rubella vaccine-associated arthropathy but do not support a role for quantitative differences in rubella IgG and IgA antibody in the pathogenesis of this syndrome.

IgA antibodies against P30 as markers of congenital and acute toxoplasmosis

Specific IgA antibodies against P30, a major surface protein of Toxoplasma gondii were sought in 198 serum samples (from 133 patients) by means of a double-sandwich enzyme-linked immunosorbent assay. These antibodies were detected in all cases of acute toxoplasmosis but in no cases of chronic toxoplasmosis nor in seronegative patients. They were not detected in samples from patients with "natural IgM antibodies" or in those containing rheumatoid factor or antinuclear antibodies. Among 26 infants whose mothers were infected during pregnancy, anti-P30 IgA antibodies were exclusively detected in the samples from the 8 infected infants, although anti-P30 IgM antibodies were detected in only 3 of the infected infants. No uninfected infant had IgA, though 5 had IgM at birth. Thus, the detection of IgA anti-P30 antibodies seems a better means than the detection of IgM antibodies of identifying infected infants, which is very important for treatment. In addition, the very early detection of IgA antibodies may be important for the diagnosis of acute toxoplasmosis, especially during pregnancy and perhaps also in patients infected by human immunodeficiency virus.

Immunoglobulin A antibodies to Trypanosoma cruzi antigens in digestive forms of Chagas' disease

In an attempt to find a serological marker for the diagnosis of chronic digestive forms of Chagas' disease, we compared amastigote and trypomastigote antigens obtained from immunosuppressed mice infected with Trypanosoma cruzi (Y strain) with conventional epimastigote antigens to search for immunoglobulin A (IgA) antibodies. A total of 255 serum samples from patients with acute and chronic (indeterminate, digestive, and cardiac) forms of Chagas' disease and with nonchagasic diseases and from healthy individuals were studied. Amastigote antigens proved to be the most adequate for our purpose, since IgA antibodies could be detected in 23 of 25 serum samples from patients with digestive forms, with relative indices of sensitivity, specificity, and efficiency of 0.920, 0.911, and 0.912, respectively. These antigens also showed high reactivity with IgA antibodies, with a geometric mean titer of 16,635 (12.7 log2). IgA antibodies were detected in 16 of 28 serum samples from patients with the acute form as well, but this clinical form is easily distinguished from the chronic form by the demonstration of IgM antibodies. Poor results were seen with trypomastigote and epimastigote antigens. The finding of IgA antibodies in about 20% of indeterminate forms and 20% of cardiac forms, although in low titers, requires further investigation to ascertain their role as an early signal of gastrointestinal lesions. In addition, the amastigote antigens described here seem more convenient for use in endemic areas than those obtained from cell cultures because of their lower cost.

Investigation of human immune response to Micropolyspora faeni antigens by enzyme-linked immunoelectrodiffusion assay and immunoblotting

Immune response to Micropolyspora faeni was analyzed in 10 patients suffering from farmer's lung by two techniques: enzyme-linked immunoelectrodiffusion assay (ELIEDA) and immunoblotting. ELIEDA revealed the presence in all patients of various specific immunoglobulin G (IgG), IgM, IgA, and IgE antibodies, with the number of arcs ranging from 4 to 19. M. faeni proteins were isolated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, transferred to nitrocellulose, and immunoblotted with human sera and specific immunoglobulin-peroxidase conjugates. In immunoblotting, the predominant immunoglobulin class was IgG for all patients. At least 20 bands ranging from 15,000 to 60,000 in molecular weight were observed in a highly positive serum, whereas IgM- and IgA-specific reactivity was directed mainly to the 28,000- and 49,000-molecular-weight bands; M. faeni-specific IgE antibodies appeared less often. The rheumatoid factor (IgM-RF), which also had high titers in these patients (greater than 1/512), interfered with ELIEDA, while only slightly interfering with the immunoblotting detection of specific IgM. This latter technique provided a better characterization of immune response in patients with farmer's lung than ELIEDA did and should also permit discrimination of recently exposed individuals from chronic patients. Moreover, this technique should make it possible to determine whether the response of one particular immunoglobulin class to an antigen fraction can be associated with a specific state of the disease.

Screening test for rheumatic diseases: a combined enzyme immunoassay of rheumatoid factors and antibodies to DNA and extractable nuclear antigens

Three hundred and one sera from patients with rheumatic and other diseases were investigated using a simple enzyme immunoassay for screening of rheumatoid factors and antinuclear antibodies. The assay had a sensitivity of 77% for systemic lupus erythematosus, 90% for the primary sicca syndrome, and 89% for rheumatoid arthritis. Only 13% of sera from patients with chronic non-rheumatic diseases were positive. The test was further evaluated in a group of patients with suspected rheumatic disease who were followed up for six to 12 months. The test was positive in 16 of 17 sera from patients with connective tissue diseases but in only seven of 36 sera (19%) from patients with non-inflammatory joint diseases. None of the four patients with reactive arthritis was positive by this test. The sensitivity of the assay was comparable with that of the agglutination and immunofluorescence tests for rheumatoid factors and antinuclear factors. For the screening of rheumatoid factor and antinuclear antibodies this kind of test panel offers a simple alternative to the conventional tests for small clinical laboratories and for those in which the autoantibody tests could be automated, as the assay can be performed in one working day and only one dilution of serum is needed to obtain a quantitative result.

Virus-specific serum IgG, IgM, and IgA antibodies in cytomegalovirus mononucleosis patients as determined by immunoblotting technique

The immune response to individual human cytomegalovirus (CMV) structural polypeptides was studied in paired sera from 15 adult CMV mononucleosis (CMV-MN) patients and healthy controls by immunoblotting technique (IB). IgM and IgG antibodies to at least 11 structural polypeptides with molecular weights of 28K, 49K, 55K, 57K, 66-70K, 82K, 87K, 110K, 150K, 205K, and 235K were detected in the patients' sera in the serum sample obtained in the acute phase of the disease. IgA antibodies to polypeptides with molecular weights of 66-70K, 82K, 110K, and 150K were also detected in these sera. In healthy seropositive adults, IgG antibodies with the same molecular weight polypeptides, excluding the 205K and 235K polypeptides, were detected as in convalescent CMV-MN patients. A prominent reactivity of IgM and IgA antibodies to the 66-70K and 150K polypeptides was noted in the acute sera from all the CMV-MN patients examined, but not in a number of late convalescent sera. The potential implications of these findings in the development of specific serological tests are discussed.

Enzyme-linked immuno-filtration assay (ELIFA) for the detection of IgG, IgM, IgA and IgE antibodies against Aspergillus fumigatus

The enzyme-linked immuno-filtration assay (ELIFA) permits detection of serological precipitating systems preformed by immunoelectro-diffusion on cellulose acetate strips and simultaneous characterization of immunoglobulins G, M, A and E specific for antigens of Aspergillus fumigatus. We selected 36 sera from 9 patients who were followed up regularly and who suffered from aspergilloma (5 cases), allergic bronchopulmonary aspergillosis (2 cases), Aspergillus bronchitis and invasive aspergillosis (one case each). All of them possessed an IgG-reactive band with chymotrypsin activity. Four different IgE bands were found by ELIFA; one of them was common to all the patients who had anti-A. fumigatus IgE (7 cases out of 9). The IgA and IgM antibodies found in 7 cases out of 9 were both recognized by the same antigenic component but these fractions were distinct from those reacting with the IgE.

Antibody response to the rubella virus structural proteins in infants with the congenital rubella syndrome

Forty-five serum samples from 31 newborns and infants with the congenital rubella syndrome (CRS) were tested by immunoprecipitation to determine their antibody spectra to each of the structural proteins of rubella virus. Most sera (37/45) contained little or no E2 protein-specific antibody, but some (6/45) precipitated a greater amount of the E2 glycoprotein than the E1 glycoprotein. The relative E1/E2 ratio was found to decrease with time when serial serum samples from the same patient were tested. No correlation between the IgG class hemagglutination inhibition antibody titers and the E1/E2 ratio could be demonstrated. However, in some serum specimens relatively high neutralizing antibody titers were correlated with immunoprecipitation of the E2 glycopolypeptide. None of the CRS sera reacted well with the C protein. The immunoprecipitation patterns found in CRS sera were qualitatively different from those observed in a series of 25 sera from young adults with conventional serologic evidence of rubella immunity following natural infection. All of the natural immune sera recognized each of the three structural polypeptides of rubella virus.

Differences in antibody responses with rapid agglutination tests for the detection of rubella antibodies

Rapid agglutination tests (Rubaquick, Rubascan, and Rubacell) were used to screen sera (374 from immune and 124 from susceptible patients) for rubella immunity. Compared with enzyme immunoassay (Rubazyme) the erythrocyte agglutination assays (Rubaquick and Rubacell) were greater than 98% sensitive and 92 to 96% specific. The latex test (Rubascan) was sensitive (97.8%) and specific (96.8%) on undiluted serum but only 68.7% sensitive on serum diluted 1:10. Although the three rapid assays detected a substantial number of positive sera within 3 months of rubella immunization, a large number of variable responses were seen after infection with rubella. Analysis of discordant results suggests that these tests may be effectively used for immunity screening. The different individual assay results observed on low-titered sera or blood collected shortly after infection or immunization may not be comparable, because each assay has a different antigenic component on the agglutinin.

An enzyme immunoassay for immunoglobulin M antibodies to Toxoplasma gondii which is not affected by rheumatoid factor or immunoglobulin G antibodies

An enzyme-linked immunosorbent assay (ELISA) for total antibodies to Toxoplasma gondii was modified to measure specific immunoglobulin M (IgM) antibodies. The assay requires three incubation periods totaling 2 h and enzyme-labeled-heavy-chain-specific antibodies to human IgM. The objective read-out in absorbance was normalized to percent of a standardized positive control for interpretations. No difference was observed between the assay results with or without previous absorption of the samples by Staphylococcus aureus protein A to remove most of the IgG antibodies. Addition of serum containing very high levels of IgG antibodies to another containing both IgG and IgM antibodies did not change the IgM assay values for the latter. None of the 22 sera containing high levels of IgM rheumatoid factor (RF) gave positive ELISA IgM results, even though 8 of them also had high levels of IgG toxoplasma antibodies. Mixtures of sera containing high concentrations of RF with sera having high levels of IgG toxoplasma antibodies also failed to show any false-positive reactions in the IgM toxoplasma assay. Thus, this ELISA for T. gondii IgM antibodies was not affected by IgG toxoplasma antibodies and RF.