Identification, production and assessment of two Toxoplasma gondii recombinant proteins for use in a Toxoplasma IgG avidity assay

ABSTRACT Risk of mother-to-child transmission of Toxoplasma gondii during pregnancy is much greater in women who are exposed to primary T. gondii infection (toxoplasmosis) after conception compared to those who were exposed to the infection before conception. Therefore, laboratory tests that help classify recent primary toxoplasmosis are important tools for the management of pregnant women suspected to have T. gondii exposure. Detection of Toxoplasma IgM (Toxo IgM) is a sensitive indicator of primary toxoplasmosis, but the indicator specificity is low because sometimes natural IgM antibodies react with Toxoplasma antigens in the absence of the infection. Furthermore, Toxo IgM sometimes persists in blood serum for several months or years following the primary infection. In recent decades, Toxo IgG avidity assay has been used as a standard diagnostic technique for a better estimation of the infection acquisition time and identification of the primary T. gondii infection during pregnancy. Avidity is described as the aggregate strength; by which, a mixture of polyclonal IgG molecules reacts with multiple epitopes of the proteins. This parameter matures gradually within 6 months of the primary infection. A high Toxo IgG avidity index allows a recent infection (less than 4 months) to be excluded, whereas a low Toxo IgG avidity index indicates a probable recent infection with no exclusions of the older infections. This minireview is based on various aspects of T. gondii IgG avidity testing, including (i) description of avidity and basic methods used in primary studies on T. gondii IgG avidity and primary infections; (ii) importance of IgG avidity testing in pregnancy; (iii) result summary of the major studies on the use of T. gondii IgG avidity assay in pregnancy; (iv) brief explanation of the T. gondii IgG avidity values in newborns; (v) result summary of the major studies on T. gondii IgG avidity and PCR; (vi) discussion of commercially available T. gondii IgG avidity assays, including newer automated assays; and (vii) current issues and controversies in diagnosis of primary T. gondii infections in pregnancy.

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Toxoplasma gondii specific IgG avidity assay: Role and implication in the confirmatory diagnosis of acute toxoplasmosis in seropositive pregnant women

Bangabandhu Sheikh Mujib Medical University Journal ◽

10.3329/bsmmuj.v9i2.29263 ◽

2016 ◽

Vol 9 (2) ◽

pp. 96

Author(s):

Chowdhury Rafia Naheen ◽

Shirin Tarafder ◽

Humayun Sattar ◽

Shafinaz Khan

Keyword(s):

Toxoplasma Gondii ◽

Pregnant Women ◽

Acute Infection ◽

High Avidity ◽

Past Infection ◽

Congenital Transmission ◽

Avidity Assay ◽

Igg Avidity ◽

Avidity Test ◽

Specific Igg

This study was undertaken to apply Toxoplasma gondii specific IgG avidity test in seropositive pregnant women to differentiate acute and past infection. T. gondii specific IgG avidity test was conducted in 39 seropositive pregnant women and their pregnancy outcomes were observed later on. Out of 39 T. gondii seropositive pregnant women 33 (84%) were only IgG positive and 6 (15.4%) were both IgG-IgM positive. All the IgG positive cases (100%) and 2(33.3%) IgG-IgM positive cases had high avidity antibodies and they gave birth to healthy babies. Rest of the 4 (66.7%) IgG-IgM positive women had low avidity and 50% of them had abortion and 50% gave birth to unhealthy babies. This reveals that the seropositive mothers having high IgG avidity had past infection and no risk of congenital transmission. Seropositive mothers having low IgG avidity had acute infection and so congenital transmission occurred. Presence of T. gondii specific IgG and IgM antibody does not indicate acute infection always. IgG-IgM positive pregnant women should be further evaluated by IgG avidity assay to confirm acute infection.

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Measles Virus IgG Avidity Assay for Use in Classification of Measles Vaccine Failure in Measles Elimination Settings

Clinical and Vaccine Immunology ◽

10.1128/cvi.00406-12 ◽

2012 ◽

Vol 19 (11) ◽

pp. 1810-1817 ◽

Cited By ~ 38

Author(s):

Sara Mercader ◽

Philip Garcia ◽

William J. Bellini

Keyword(s):

Measles Virus ◽

Area Under The Curve ◽

Epidemiological Data ◽

Diagnostic Tools ◽

High Avidity ◽

Characteristic Analysis ◽

Vaccine Failure ◽

Avidity Assay ◽

Igg Avidity

ABSTRACTIn regions where endemic measles virus has been eliminated, diagnostic assays are needed to assist in correctly classifying measles cases irrespective of vaccination status. A measles IgG avidity assay was configured using a commercially available measles-specific IgG enzyme immunoassay by modifying the protocol to include three 5-min washes with diethylamine (60 mM; pH 10.25) following serum incubation; serum was serially diluted, and the results were expressed as the end titer avidity index. Receiver operating characteristic analysis was used for evaluation and validation and to establish low (≤30%) and high (≥70%) end titer avidity thresholds. Analysis of 319 serum specimens expected to contain either high- or low-avidity antibodies according to clinical and epidemiological data indicated that the assay is highly accurate, with an area under the curve of 0.998 (95% confidence interval [CI], 0.978 to 1.000), sensitivity of 91.9% (95% CI, 83.2% to 97.0%), and specificity of 98.4% (95% CI, 91.6% to 100%). The assay is rapid (<2 h) and precise (standard deviation [SD], 4% to 7%). In 18 samples from an elimination setting outbreak, the assay identified 2 acute measles cases with low-avidity results; both were IgM-positive samples. Additionally, 11 patients (15 samples) with modified measles who were found to have high-avidity IgG results were classified as secondary vaccine failures; one sample with an intermediate-avidity result was not interpretable. In elimination settings, measles IgG avidity assays can complement existing diagnostic tools in confirming unvaccinated acute cases and, in conjunction with adequate clinical and epidemiologic investigation, aid in the classification of vaccine failure cases.

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IgG avidity in the serodiagnosis of acute Toxoplasma gondii infection: a multicenter study

Clinical Microbiology and Infection ◽

10.1111/j.1469-0691.1996.tb00196.x ◽

1996 ◽

Vol 2 (1) ◽

pp. 25-29 ◽

Cited By ~ 35

Author(s):

Alessandra Sensini ◽

Susanna Pascoli ◽

Daniela Marchetti ◽

Roberto Castronari ◽

Maurizio Marangi ◽

...

Keyword(s):

Toxoplasma Gondii ◽

Multicenter Study ◽

Igg Avidity ◽

Toxoplasma Gondii Infection

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

Journal of Virological Methods ◽

10.1016/j.jviromet.2005.06.003 ◽

2005 ◽

Vol 130 (1-2) ◽

pp. 59-65 ◽

Cited By ~ 18

Author(s):

Rasool Hamkar ◽

Somayeh Jalilvand ◽

Talat Mokhtari-Azad ◽

Keramat Nouri Jelyani ◽

Hosein Dahi-Far ◽

...

Keyword(s):

Immune Response ◽

Enzyme Immunoassay ◽

Secondary Immune Response ◽

Rubella Vaccine ◽

Avidity Assay ◽

Igg Avidity

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Longitudinal Study of SARS-CoV-2 Antibody Characteristics Using Label-Free Immunoassays

American Journal of Clinical Pathology ◽

10.1093/ajcp/aqab191.063 ◽

2021 ◽

Vol 156 (Supplement_1) ◽

pp. S32-S32

Author(s):

Y R Luo ◽

C Yun ◽

A H Wu ◽

K L Lynch ◽

I Chakraborty

Keyword(s):

Symptom Onset ◽

Neutralizing Antibody ◽

Label Free ◽

Serum Samples ◽

Neutralization Activity ◽

Antibody Avidity ◽

Avidity Assay ◽

Initial Rise ◽

Igg Avidity ◽

Antibody Titers

Abstract Introduction/Objective Since the start of the COVID-19 pandemic, much research has focused on the kinetics and magnitude of humoral immune response. With the advantages of monitoring real-time immunoreactions, label-free immunoassay (LFIA) is becoming a powerful tool in serology studies. We have developed LFIAs to measure SARS- CoV-2 antibody avidity and neutralization activity in a cohort of COVID-19 patients and determine if they correlate with antibody concentration. Serial serum samples collected from mild to severe COVID-19 patients were measured out to 8 months post-symptom onset to determine the durability of the neutralizing antibody response. Methods/Case Report Based on thin-film interferometry technology, we established a label-free IgG avidity assay and a label-free surrogate virus neutralization test (LF-sVNT). For measurement, sensing probes pre-coated with receptor-binding domain (RBD) of SARS-CoV-2 spike protein are applied to serum samples containing SARS-CoV-2 antibodies. The label-free IgG avidity assay measures the binding strength between RBD and IgG under urea dissociation. The LF-sVNT analyzes the binding ability of RBD to ACE2 after neutralizing RBD with antibodies. Results (if a Case Study enter NA) IgG avidity indices and neutralizing antibody titers (IC50) were determined from serum samples (n=246) from COVID-19 patients (n=113). IgG concentrations were measured using a fluorescent immunoassay. The neutralizing antibody titers showed a weak correlation with IgG concentrations and no correlation with IgG avidity indices. Over the time course up to 8 months post-symptom onset, IgG concentrations and neutralizing antibody titers presented similar trends: an initial rise, plateau and then in some cases a gradual decline after 40 days. The IgG avidity indices, in the same cases, plateaued after the initial rise. Conclusion The results demonstrated that LFIA could be used an excellent solution in the determination of SARS- CoV-2 antibody characteristics. The study found that IgG concentration and neutralizing antibody titer declined over time, while IgG avidity index remained constant after reaching a plateau. The decline of antibody neutralization activity can be attributed to the reduction in antibody quantity rather than the deterioration of antibody quality, as measured by antibody avidity.

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Rapid diagnosis of hantavirus disease with an IgG-avidity assay

The Lancet ◽

10.1016/0140-6736(91)92235-t ◽

1991 ◽

Vol 338 (8779) ◽

pp. 1353-1356 ◽

Cited By ~ 103

Author(s):

K. Hedman ◽

A. Vaheri ◽

M. Brummer-Korvenkontio

Keyword(s):

Rapid Diagnosis ◽

Avidity Assay ◽

Igg Avidity

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Correlation between specific IgM levels and percentage IgG-class antibody avidity to Toxoplasma gondii

Revista do Instituto de Medicina Tropical de São Paulo ◽

10.1590/s0036-46652008000400010 ◽

2008 ◽

Vol 50 (4) ◽

pp. 237-242 ◽

Cited By ~ 7

Author(s):

Marcel Leite ◽

Sonia Siciliano ◽

Lucia Silvieri A. Rocha ◽

Teresa R. Justa ◽

Katia Regina César ◽

...

Keyword(s):

Toxoplasma Gondii ◽

Acute Phase ◽

Turnaround Time ◽

Antibody Avidity ◽

Igg Avidity ◽

Avidity Test ◽

Evaluation Test ◽

Fetal Malformations ◽

Two Parameters ◽

Class Antibody

Toxoplasmosis is an usually asymptomatic worldwide disseminated infection. In its congenital presentation it may lead to abortion or fetal malformations. Antenatal evaluation is considered of paramount importance to identify seronegative women and allow for prophylaxis. Recent improvements in sensitivity of IgM tests has made IgM detection an extremely protracted acute phase marker, and IgG avidity evaluation test became necessary. Observation has shown that a correlation can be established between IgM levels and avidity percentages, suggesting that frequently the avidity test may not be necessary. In this study we analyzed Toxoplasma gondii IgM levels of 202 samples and their IgG avidity percentages, in order to define specific levels whose IgM quantification could by itself define serodiagnosis and therefore make the avidity evaluation unnecessary. We showed that for IgM levels bellow 2.0 and above 6.0 serodiagnosis of toxoplasmosis could be established without need of IgG avidity test. IgM levels between these two parameters are associated with varying avidity indexes highlighting the importance of its evaluation as a means to confirm toxoplasmosis. Following this demonstration it was possible to avoid the avidity test for 75% of the cases, to reduce the turnaround time and to reduce costs.

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