Abstract
The aim of this work was to evaluate the utility of ELISA-based testing of total IgG (IgGt) antibodies and its subclasses (IgG1, IgG2, IgG3 and IgG4) against soluble (STAg) and recombinant (rSAG1 and rMIC3) antigens of Toxoplasma gondii for diagnosing congenital toxoplasmosis. Sera from 217 newborns initially testing positive for specific IgM in filter paper dried blood spots were tested for specific IgM and IgG by ELFA-VIDAS. Congenital toxoplasmosis was confirmed in 175 and ruled out in 42 infants. The validity of the ELISA tests was determined using the persistence of IgG antibodies (ELFA-VIDAS kit) at the end of 12 months, which is considered the reference test for the diagnosis of congenital toxoplasmosis. The frequency of positivity with IgGt against STAg, rSAG1 and rMIC3 was found in 97.2%, 96.3% and 80.2%, respectively, of the newborns with confirmed congenital toxoplasmosis. IgG1 reacted with all three antigens, while IgG3 and IgG4 reacted preferentially with rMIC3. Higher mean values of reactivity (sample optical density/cut-off) were found for all subclasses when using rMIC3. All of the antigens showed high sensitivity and low specificity in detecting anti-T. gondii IgGt and IgG1 and low sensitivity and high specificity in detecting IgG3 and IgG4. In conclusion, the combined detection of IgG antibody subclasses against recombinant toxoplasmic antigens may be useful for the early diagnosis of congenital toxoplasmosis.
Highlights
Toxoplasmosis is a worldwide zoonosis caused by Toxoplasma gondii, an intracellular protozoan of a heteroxenic life-cycle that is capable of infecting a variety of warm-blooded vertebrates
This study evaluated the use of soluble (STAg) and recombinant T. gondii antigens in ELISA-based testing for total IgG antibodies (IgGt) and its subclasses in serum samples of newborns with congenital toxoplasmosis
IgGt and its subclasses reacting with STAg, rSAG1 and rMIC3 were assessed in the sera of the 217 children positive for IgM
Summary
Toxoplasmosis is a worldwide zoonosis caused by Toxoplasma gondii, an intracellular protozoan of a heteroxenic life-cycle that is capable of infecting a variety of warm-blooded vertebrates. This study evaluated the use of soluble (STAg) and recombinant (rSAG1 and rMIC3) T. gondii antigens in ELISA-based testing for total IgG antibodies (IgGt) and its subclasses in serum samples of newborns with congenital toxoplasmosis. Patients and clinical samples - This study was conducted as part of a prospective investigation on the impact of CT in the state of Minas Gerais from 1 November 2006-31 May 2007 with children participating in the State Program for Neonatal Screening (Vasconcelos-Santos et al 2009) In this program, filter paper-dried blood samples from 146,307 newborns were tested for anti-T. gondii IgM (TOXO IgM Q-preven®, Symbiosis, Leme, Brazil) with 217 presenting positive or inconclusive serological results. Recombinant antigens were expressed in Escherichia coli as fusion proteins with glutathione S-transferase (GST)
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