Rubella IgG total antibody avidity and IgG subclass-specific antibody avidity assay and their role in the differentiation between primary rubella and rubella reinfection

Positive predictive value of seroconversion or positive rubella IgM in diagnosis of maternal rubella infection: Seven-years review of French National Reference Laboratory for Rubella

BACKGROUND

In France, as in most developed countries, childbearing age women are routinely screened for rubella antibodies to identify and vaccinate susceptible women. Immunity to rubella is usually determined by measuring the rubella virus-specific immunoglobulin G (RV-IgG). In case of seroconversion for RV-IgG and/or positive RVIgM during pregnancy, laboratories usually send serum samples to the French National Reference Laboratory (FNRL) for Rubella in order to perform complementary investigations and confirm or exclude rubella infection during pregnancy.

OBJECTIVE

Our aim is to report results of these investigations during a seven-year period (2013-2019) and evaluate the positive predictive value (PPV) of RV-IgG seroconversion or positive RV-IgM to diagnose maternal rubella infection in France.

STUDY DESIGN

Between 2013 and 2019, 5398 serum samples collected from 4104 pregnant women, were addressed to FNRL because of RV-IgG seroconversion (N=899) or positive RV-IgM (N=3205). Additional serological tests were performed, mainly immunoblot (to look for the presence of anti-E1 protective antibody) and RV-IgG avidity (to exclude or confirm primary infection).

RESULTS

Overall, for 3724/4104 (90.8 %) women, rubella primary-infection during pregnancy was formally excluded and maternal rubella primary-infection was only confirmed in 46/4104 (1.1 %) cases.

CONCLUSION

Clinicians and biologists should be particularly aware that RV-IgG seroconversion or positive RV-IgM, in the current context of low RV circulation in France are most often not rubella primary infections. PPV of seroconversion to assess maternal rubella primary infection is as low as 0.2 % (95 % CI: 0 %; 0.5 %) and PPV of positive RV-IgM is only of 1.4 % (95 % CI: 0.99 %; 1.81 %).

Characterization of antibody response in neuroinvasive infection caused by Toscana virus

OBJECTIVES

Among sandfly-borne pathogens, Toscana virus (TOSV) is a prominent cause of summer meningitis in Mediterranean Europe. Here, we assessed the kinetics of anti-TOSV antibodies over time in 41 patients diagnosed with TOSV meningitis or meningoencephalitis in northeastern Italy.

METHODS

Acute and follow-up serum samples were collected up to 20 months after diagnosis of TOSV infection and tested for the presence of specific antibody using immunoenzymatic and indirect immunofluorescence assays. In addition, maturation of anti-TOSV IgG over time was evaluated as well as production of neutralizing antibodies.

RESULTS

Specific IgM and IgG response was present at diagnosis in 100% of patients; TOSV-specific IgM and IgG were detected in patients' sera up to 6 and 20 months after diagnosis, respectively. The avidity index (AI) increased over the first month after infection in 100% of patients and most cases exceeded 60% by Day 30 post infection. The AI subsequently plateaued then declined at 20 months after diagnosis. Finally, neutralization assay to TOSV was performed in 217 sera collected from 41 patients; 69.6% of tested samples resulted in reactive and moderate levels of neutralizing antibodies observed during all phases of infection despite high titres of total anti-TOSV IgG.

CONCLUSIONS

Specific antibody response develops rapidly and is long-lasting for neuroinvasive TOSV infection. Serodiagnosis of neuroinvasive TOSV requires simultaneous detection of specific IgM and IgG. Moderate levels of neutralizing antibodies were maintained over the study period, while the protective role of antibodies lacking neutralizing activity is unclear and requires further evaluation.

Temporal evolution of human autoantibody response to cytoplasmic rods and rings structure during anti-HCV therapy with ribavirin and interferon-α

Autoantibodies to inosine monophosphate dehydrogenase-2 (IMPDH2), an enzyme involved in de novo biosynthesis of guanine nucleotides, are observed in a subset of hepatitis C virus (HCV) patients receiving interferon alpha (IFN-α) plus ribavirin. Anti-IMPDH2 antibodies display a peculiar cytoplasmic "rod/ring" (RR) pattern in IIF-HEp-2. We examined the dynamics of anti-RR autoimmune response with respect to immunoglobulin isotypes, titer, avidity, and protein targets in 80 sequential samples from 15 HCV patients (plus 12 randomly selected anti-RR-positive, totalizing 92 samples) collected over an 18-month period, including samples collected before, during, and after IFN-α + ribavirin treatment. Immunoprecipitation showed reactivity with the 55 kDa IMPDH2 protein in 12/15 patients (80 %) and 11/15 (73 %) reacted with IMPDH2 in a sandwich ELISA. During treatment, anti-IMPDH2 autoantibodies hit their highest levels after 6-12 months of treatment and decreased post-treatment, while anti-HCV antibodies levels were stable over time. Anti-IMPDH2 IgM levels increased up until the sixth month of treatment and remained stable thereafter, while IgG levels increased steadily up to the twelfth month. Both IgG and IgM decreased during the post-treatment period. IgG avidity increased steadily up to the twelfth month of treatment. In conclusion, this study showed that the temporal kinetics of IFN-α + ribavirin-induced humoral autoimmune response to IMPDH2 exhibited a considerably delayed pace of increase in antibody levels and avidity as well as in isotype class switch in comparison with a conventional humoral response to infectious agents. These unique findings uncover intriguing differences between the autoimmune response and the immune response to exogenous agents in humans.

Virale Infektionen: RNA-Viren

Rhinoviren sind die Haupterreger der sog. Erkältungskrankheiten. Eine wichtige Rolle spielen sie auch als Auslöser von Asthmaattacken.

Es findet eine stete Kozirkulation mehrerer Serotypen statt, im gemäßigten Klima gibt es Herbst-, Winter- und Frühjahrsepidemien, die Übertragung geschieht weit häufiger über infizierte Sekrete als durch Aerosole.

Rhinoviren gehören zu den Picornaviren. Rhinoviren sind sehr kleine Viren mit einem positiven Einzelstrang-RNA-Genom ohne Lipidhülle und daher gegen Detergens enthaltende Desinfektionsmittel sehr resistent. Sie sind empfindlich gegen Umgebungs-pH außerhalb des Bereichs 5,0–7,5.

Zurzeit bilden sie zusammen mit den Enteroviren das Genus Enterovirus der Picornaviren. Serologisch lassen sich über 100 Typen unterscheiden. Kennzeichnend ist die Bindungsfähigkeit an das von den meisten Rhinoviren für die Zelladsorption genützte ICAM-1 (interzelluläres Adhäsionsmolekül).

Nach einer Inkubationszeit von 1–3 Tagen tritt Schnupfen auf, die höchste Viruskonzentration im Nasensekret nach 2–4 Tagen, wiederum nach 2–4 Tagen bei disponierten Patienten auch bronchiale Obstruktion. Es konnte gezeigt werden, dass zu dieser Zeit auch Virus-RNA im Bronchialepithel vorhanden ist. Die postinfektiöse bronchiale Hyperreagibilität korreliert mit der Dauer des Virus-RNA-Nachweises im Nasopharynx. Die Immunität ist im Wesentlichen abhängig von der nur sehr kurzen Anwesenheit sekretorischer spezifischer IgA-Antikörper. Die bei den Serotypen beobachtbare Kreuzreaktivität spiegelt sich nicht in Kreuzimmunität wider.

Rubella antibody screening during pregnancy in an urban area of Northern Italy

Various countries have implemented anti-rubella vaccination campaigns with the main aim of preventing congenital infection. In 2003, Italy joined the European WHO programme for the elimination of congenital rubella and issued a special healthcare plan, one of the objectives of which was to reduce the proportion of rubella-susceptible pregnant women to less than 5% by 2005. The aim of this study was to determine the percentage of seronegative pregnant women after the implementation of this plan. Anti-rubella IgG and IgM antibodies were sought in 2385 pregnant women who attended our hospital for serological screening between 1 July 2008 and 30 June 2010. They included 750 women of foreign origin (31.4%). Eight percent of the women were anti-rubella seronegative: 6.2% of the Italians and 11.7% of the non-Italians. Among the women of foreign origin, the percentage of seronegativity ranged from 5.6% of those coming from Eastern Europe to 17.7% of those coming from Latin America. The level of seropositivity among women of Italian origin is high, although the objective of ensuring less than 5% of susceptible pregnant women has not yet been quite reached in our area. However, particular attention needs to be given to women coming from geographical areas characterised by different epidemiologies and vaccination strategies because the percentage of seronegativity is in some cases double that of Italian women.

Development of a rapid and convenient method for determination of rubella virus-specific immunoglobulin G avidity

We describe here a rapid and semiautomated method for the determination of rubella virus immunoglobulin G (IgG) avidity with the VIDAS instrument. A total of 153 serum samples from persons with naturally acquired rubella virus infections (n = 98), from vaccinated persons (n = 44), and from patients with autoantibodies (n = 11) were included in this study. The rubella virus-specific IgG avidity assay we developed for the VIDAS instrument was evaluated by comparison with an in-house method. Results obtained with the VIDAS instrument allow considering this method valuable to help confirm or exclude acute primary infection or recent vaccination.

Virale Infektionen

Adenoviren verursachen im Kindesalter Krankheiten der Atemwege und des Darms, aber auch Krankheiten der Harnwege, der Lymphorgane und kardiologische und neurologische Manifestationen werden beobachtet. Einige typische Krankheitsbilder können klinisch diagnostiziert werden.

Immunoglobulin G avidity in differentiation between early and late antibody responses to West Nile virus

In 1999 West Nile virus (WNV) surfaced in the United States in the city of New York and spread over successive summers to most of the continental United States, Canada, and Mexico. Because WNV immunoglobulin M (IgM) antibodies have been shown to persist for up to 1 year, residents in areas of endemicity can have persistent WNV IgM antibodies that are unrelated to a current illness with which they present. We present data on the use of IgG avidity testing for the resolution of conflicting data arising from the testing of serum or plasma for antibodies to WNV. Thirteen seroconversion panels, each consisting of a minimum of four samples, were used. All samples were tested for the presence of WNV IgM and IgG antibodies, and the avidity index for the WNV IgG-positive samples was calculated. Panels that exhibited a rise in the WNV IgM level followed by a sequential rise in the WNV IgG level were designated "primary." Panels that exhibited a marked rise in the WNV IgG level followed by a sequential weak WNV IgM response and that had serological evidence of a prior flavivirus infection were designated "secondary." All samples from the "primary" panels exhibited low avidity indices (less than 40%) for the first 20 to 30 days after the recovery of the index sample (the sample found to be virus positive). All of the "secondary" samples had elevated WNV IgG levels with avidity indices of > or =55%, regardless of the number of days since the recovery of the index sample. These data demonstrate that it is possible to differentiate between recent and past exposure to WNV or another flavivirus through the measurement of WNV IgG avidity indices.

Assessment of IgM enzyme immunoassay and IgG avidity assay for distinguishing between primary and secondary immune response to rubella vaccine

The primary test for the laboratory confirmation of rubella is IgM serology. It is important to distinguish IgM reactivity caused by primary infection from that caused by reinfection or persistence, especially in pregnant women; as termination of pregnancy is considered when primary rubella is diagnosed during the first trimester. In this study, the performance of rubella IgM enzyme immunoassay (IgM-EIA) and rubella IgG avidity assay were compared using well-defined panels of sera from persons vaccinated against rubella and commercial rubella IgM and IgG enzyme immunoassay kits (Dade Behring, Marburg, Germany). The sensitivity and specificity of rubella IgM-EIA were found to be 77.4 and 97.9%, respectively, while the results for rubella IgG avidity assay were 100 and 100%. IgG avidity assay showed higher positive and negative predictive values than the IgM-EIA (100 and 100% compare to 96.9 and 82.9%). In conclusion, the rubella IgG avidity assay is more sensitive and specific than IgM-EIA for differential detection of primary rubella infection from rubella reinfection.

Laboratory investigations are indispensable to monitor the progress of measles elimination--results of the German Measles Sentinel 1999-2003

BACKGROUND

The elimination of measles is a goal set by the World Health Organisation to be reached by 2010 in the European region.

OBJECTIVES

To enhance the measles surveillance in Germany, a country-wide laboratory supported a sentinel was established.

STUDY DESIGN

A network of >1200 representatively distributed practitioners reported detailed data on all clinically diagnosed cases and provided specimens for laboratory diagnosis.

RESULTS

A total of 3225 suspected cases were reported between October 1999 and December 2003. The incidence in Western Germany decreased from >15 cases per 100,000 population to one case in 2003, while in Eastern Germany <1 case per 100,000 population was observed during these years. Laboratory investigations were undertaken in 40% of cases in 2000/2001. This rate increased to 79% in 2003. Simultaneously, the rate of confirmed cases dropped from 60% in the former years to 23% in 2003. Measles virus (MV) detection by serology and by PCR revealed concordant results in 92%. Most suspected cases (85%) were unvaccinated with 66% being laboratory confirmed. Only 10% of suspected cases occurred in vaccinated individuals and very few (22%) could be confirmed. Analyses of confirmed measles in vaccinated patients (n = 49) revealed 24.5% primary vaccine failures, 24.5% reinfections after successful vaccination and 31% MV infection before or shortly after vaccination. The genetic characterisation of 389 MV isolates identified eight genotypes: B3, C2, D4, D5, D6, D7, G2 and H1. Only the C2, D6 and D7 MV genotypes circulated endemically in Western Germany. The newly emerged MV D7 almost completely replaced the pre-existing C2 and D6 MVs in 2001. The few measles cases detected in Eastern Germany were mostly caused by imported MVs.

CONCLUSION

The data demonstrate that laboratory investigations including molecular methods are an indispensable tool for surveillance in all countries advanced in measles elimination.

Use of an immunoglobulin G avidity test to discriminate between primary and secondary dengue virus infections

An enzyme-linked immunosorbent assay-based immunoglobulin G (IgG) antibody avidity test was evaluated by using sera from 57 patients with acute dengue infection. Overall, 55 of 57 patients were correctly classified (27 of 27 with primary dengue and 28 of 30 with secondary dengue). We conclude that the IgG avidity test can be useful for differentiating between acute, primary, and secondary dengue infections.

Antibody subclass profile and avidity during acute and chronic human Schistosoma mansoni infection

The avidity of IgA, IgM, IgG and IgG subclass antibodies against Schistosoma mansoni soluble egg antigen (SEA) was determined by ELISA in serum samples collected in 1995 from individuals in Brazil with acute (n = 36) and chronic (n = 40) schistosomiasis. Fifteen individuals at the acute phase were also evaluated 6 months after clinical diagnosis. Predominance of low-avidity IgG, IgG1, IgG2, IgG3 and IgA characterized the acute phase. IgG4 was detected in only 2 individuals with acute disease (5.6%). Levels of anti-SEA IgM were similar between the study groups. IgG1 avidity showed the strongest association with the chronological evolution of the infection, presenting 100% of low avidity during the acute infection and reaching 100% of high avidity 6 months after. It is suggested that distinct anti-Schistosoma egg antigens subclass profile and antibody avidity characterize the clinical phases of S. mansoni infection. In particular, determination of anti-SEA IgG1 offers a new tool for the laboratory analysis of the disease.

Maturation of IgG avidity to individual rubella virus structural proteins

BACKGROUND

the structural proteins of rubella virus, the capsid protein C and the envelope glycoproteins E1 and E2 were produced in lepidopteran insect cells using baculovirus expression vectors. The C-terminal ends of the corresponding proteins were fused to a polyhistidine tag for easy and gentle purification by metal ion affinity chromatography.

OBJECTIVES

to investigate the maturation of natural and vaccinal IgG avidity against individual authentic and recombinant rubella virus (RV) structural proteins.

STUDY DESIGN

the analysis was carried out using a modified immunoblotting technique where the purified baculovirus-expressed proteins were compared with authentic rubella virus proteins. Altogether, 47 well-characterised serum samples from both naturally infected patients and vaccines were studied.

RESULTS

after natural RV infection, IgG antibodies specific for the E1 protein were predominant not only in terms of levels, but also in terms of rate and magnitude of avidity maturation. The avidity development of the IgG antibodies was much slower in vaccines than in patients after a natural RV infection.

CONCLUSIONS

together, our results indicate that IgG avidity determination in conjunction with immunoblot analysis is useful in the diagnosis of a RV infection. The recombinant proteins showed similar reactivity patterns in the immunoblot analyses as compared with the authentic viral structural proteins, suggesting suitability for serodiagnostics.

Bilateral deafness due to congenital CMV and not rubella reinfection

We report on an infant with bilateral deafness discovered at the age of 5 months caused by a retrospectively diagnosed primary maternal CMV infection after definitive exclusion of maternal rubella reinfection as a cause of fetal infection.

Immunoglobulin G avidity in the serodiagnosis of congenital rubella syndrome

The avidity of specific IgG was investigated in three infants with serologically verified congenital rubella infection. Two sera were taken from each infant: the first soon after birth and the second at the age of 23 to 31 months. Avidity of specific IgG was measured by a protein-denaturing enzyme immunoassay using urea as the elution factor, and avidity then determined by the end-point ratio (derived from antibody titration) and the avidity index methods. Rubella-specific IgM was present in the first sera of all patients, but not in the second sera. However, low avidity of specific IgG persisted in two children until age 23 to 31 months, as determined by the end-point ratio method. These data are in agreement with the findings of previous studies of avidity in congenital rubella, and show the usefulness of the protein-denaturing IgG-avidity assays employing the end-point ratio method for serological diagnosis of congenital rubella even after disappearance of specific IgM.

Maturation of rubella IgG avidity over time after acute rubella infection

BACKGROUND

As the incidence of rubella has diminished, the proportion of unspecific rubella IgM reactivity among all samples with rubella IgM reactivity has increased. It is important to distinguish IgM reactivity caused by primary infection from that caused by reinfection or persistence, especially in pregnant women, as termination of pregnancy should be considered when primary rubella is diagnosed during the first trimester.

OBJECTIVES

To elucidate the changes over time of the avidity of rubella IgG antibodies after acute rubella infection.

STUDY DESIGN

Serial samples, 84, were collected from 15 patients up to 4-5 months after acute rubella infection. Rubella specific IgG avidity was tested by the eluting principle adding 35 mM diethylamine to the washing buffer of a commercially available rubella IgG ELISA. As controls, 137 samples from women with remote rubella and 94 samples from patients with a rubelliform rash, were tested.

RESULTS

The avidity index increased steadily in all patients during the observation time. A low avidity index (< 40%) was seen up to 6 weeks after onset of rash. A high avidity index (> 60%) was not observed until 13 weeks after infection and only in four of the 15 patients during the observation time.

CONCLUSIONS

An increase of rubella IgG antibody avidity was seen during the whole observation time but was most pronounced during the first 3 months after onset of rash. Measurement of rubella IgG avidity is a good supplemental test for cases with rubella IgM reactivity to confirm or exclude a recent rubella infection.

Behaviour of IgG antibody avidity for the antigen and of IgA antibody in active cytomegalovirus, Epstein-Barr virus, herpes simplex virus and human herpes virus 6 infections. Adaptation of a commercial test

The clinical value of specific IgA and IgG antibody avidity to herpes simplex virus, cytomegalovirus, Epstein-Barr virus and human herpes virus 6 for the detection of active disease and primary infection, respectively, was evaluated. The IgG avidity test, with a break point of 55%, for the detection of primary infection, and of the IgA test for the detection of disease, were associated with a sensitivity of 97% and 64%, respectively; specificity of 100% and 82%; a positive predictive value of 100% and 76%; and a negative predictive value of 96% and 72%, respectively.

Primary and secondary infections by human parvovirus B19 following bone marrow transplantation: characterization by PCR and B-cell molecular immunology

Due to the preparative regimen necessary, bone marrow transplantation (BMT) consistently results in severe immunodeficiency, often associated with anaemia, leukopenia and thrombocytopenia. Parvovirus B19 replicates in red blood cell precursors in the bone marrow and causes erythema infectiosum ('fifth disease'), anaemia, arthritis and foetal death. We assessed the significance of B19 infections as a cause of post-BMT complications. Over 900 serial serum samples from 201 allogeneic bone marrow recipients were studied by polymerase chain reaction (PCR) and by modern serodiagnostic methods. During the first 6 months after transplantation all BMT recipients remained B19 PCR-negative. Antibody screening for B19 infections was performed up to 36 months post-transplantation. Three cases of acute B19 infection were diagnosed during the second year post-BMT. To characterize the adoptively transferred immune system we measured subclasses and avidity of anti-VP1 IgG and epitope-type specificity (ETS) of anti-VP2 IgG, which allowed functional differentiation of primary and secondary B-cell responses long after BMT. The profile of the immune response was that of a primary infection in 1 and of reinfection in 2 of the 3 acute cases. Both types were clinically mild. Infection by human parvovirus B19 is not a frequent cause of post-BMT cytopenias. The findings with the new B19 antibody markers support the concept that the donated marrow determines the type of antiviral B-cell responses.

Immunoglobulin G avidity testing in serum and cerebrospinal fluid for analysis of measles virus infection

We studied a variety of patients with measles virus infection by using avidity testing for measles virus-specific immunoglobulin G (IgG) in serum and cerebrospinal fluid samples. For the avidity testing, an Enzygnost measles IgG enzyme-linked immunosorbent assay kit was used with an 8 M urea denaturing method. With this method, low-avidity IgG (acute primary infection, avidity of < 30% within 15 days of the onset of rash) and high-avidity IgG (subacute sclerosing panencephalitis, avidity of > 75%) could be clearly distinguished by using serum samples. One patient, who developed a typical course of measles despite a previous vaccination, showed a positive IgM response with an initial low titer of measles virus-specific IgG of low avidity, but a later sample revealed a high titer of IgG of intermediate (40%) avidity, suggesting previous immunological priming. Two patients with breakthrough infection (secondary vaccine failure), both having central nervous system involvement, showed a positive IgM response with initial high titers of serum IgG of high avidity. In addition, one of the patients had a detectable level of measles-specific IgG in cerebrospinal fluid. In this patient, the avidity of both serum and cerebrospinal fluid IgG decreased during the short follow-up period. This phenomenon has never before been reported. In subacute sclerosing panencephalitis patients, the avidity of cerebrospinal fluid IgG was consistently lower than that of serum IgG. The difference in avidity between cerebrospinal fluid and serum IgG may be used as a direct indicator of intrathecal production of IgG. In conclusion, the avidity testing is simple to perform, reliable, and highly informative in the analysis of measles virus infection.

Detection of acute measles infections by indirect and mu-capture enzyme immunoassays for immunoglobulin M antibodies and measles immunoglobulin G antibody avidity enzyme immunoassay

An avidity test for measles IgG was developed and applied to the study of IgG immunoglobulin maturation kinetics in follow-up sera from 12 patients with known acute primary and convalescent measles and sera from blood donors. The avidity of the IgG anti-measles responses was measured using the 8 M urea elution technique, the results being expressed as the percentage ratio between the test readings for eluted and noneluted samples. The IgG avidity results were compared with those of indirect and mu-capture IgM enzyme immunoassays. This test was capable of detecting low-avidity antibodies at the acute phase of measles up to 7 weeks, and increasing avidity through immunosaturation during the convalescent phase. The avidity in these samples did not reach the level found in the samples of the blood donors under the follow-up time. Although a limited number of serum samples was examined, the results suggest that the measles IgG avidity test is a powerful tool for differentiating primary measles infection from the convalescent phase.

Congenital rubella syndrome despite repeated vaccination of the mother: a coincidence of vaccine failure with failure to vaccinate

Congenital rubella syndrome occurred in a boy born to a mother who had been properly vaccinated three times before conception, but developed only low titers of rubella antibody. The non-vaccinated father most likely infected the mother on a home visit during the third to fifth weeks of gestation. He served in the army and fell ill during an outbreak of a rubella-like disease in his military unit. The mother subsequently developed a slight rash, but rubella IgM antibodies were lacking and rubella infection was not suspected. This incidence demonstrates the necessity of vaccinating all children, including boys and young men, in order to reduce the number of infections and prevent further cases of congenital rubella syndrome.

Evaluation of protein-denaturing immunoassays for avidity of immunoglobulin G to rubella virus

Immunoassays have been recently developed that measure the avidity of IgG antibodies to complex microbial antigens and are suitable for serologic diagnosis of infectious diseases. In these avidity ELISAs, protein-denaturing agents are applied either as diluents of patient sera to prevent the immune complexing of IgG (diluting principle), or the preformed complexes are treated with the protein denaturants (eluting principle). We compared four protein denaturants previously used in such assays, in a diagnostic avidity ELISA for rubella IgG. Diethylamine, guanidine, thiocyanate, or urea were applied, by either principle at various concentrations, and thiocyanate, or urea were applied, by either principle at various concentrations, and thiocyanate at an optimum pH. Patient sera obtained recently after primary infection were distinguished from sera representing past rubella immunity by any protein denaturant tested by the eluting principle, which was superior to the diluting principle.

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.

Immunoglobulin G antibody avidity in patients with respiratory syncytial virus infection

The titer and avidity of respiratory syncytial virus-specific antibodies were measured in 196 serum specimens from 93 children with an acute, laboratory-confirmed respiratory syncytial virus infection. An enzyme immunoassay method based on the ability of urea to dissociate the bound antibodies with low avidity from the antigen was used. Three patterns of immune responses were observed. Children less than 6 months of age usually had low titers of antibodies with high avidity in their acute-phase serum samples. These antibodies were concluded to be of maternal origin, since their reaction pattern was similar to that of healthy adults. During the next few weeks, a slight increase in titers with a concurrent decrease in antibody avidity was observed. All children 6 to 24 months of age had low-avidity antibodies in their acute-phase serum samples, which matured to high avidity during the follow-up. On the contrary, about half of the children greater than 24 months of age had high-avidity antibodies already in the acute-phase serum samples. We conclude that the former children were experiencing primary infections with respiratory syncytial virus and the latter were experiencing reinfections. All adults with remote immunity had antibodies with high avidity.

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.

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.