Detection of Anti-Toxoplasma gondii Antibodies in Human Sera Using Synthetic Glycosylphosphatidylinositol Glycans on a Bead-Based Multiplex Assay

[Image: see text] Toxoplasmosis, while often an asymptomatic parasitic disease in healthy individuals, can cause severe complications in immunocompromised persons and during pregnancy. The most common method to diagnose Toxoplasma gondii infections is the serological determination of antibodies directed against parasite protein antigens. Here we report the use of a bead-based multiplex assay containing a synthetic phosphoglycan portion of the Toxoplasma gondii glycosylphosphatidylinositol (GPI1) for the detection of GPI1-specific antibodies in human sera. The glycan was conjugated to beads at the lipid site to retain its natural orientation and its immunogenic groups. We compared the response against GPI1 with that against the protein antigen SAG1, a common component of commercial serological assays, via the detection of parasite-specific human IgG and IgM antibodies, respectively. The GPI1-based test is in excellent agreement with the results for the commercial ELISA, as the ROC analysis of the GPI1 test shows 97% specificity and 98% sensitivity for the assay. GPI1 was a more reliable predictor for a parasite-specific IgM response compared to SAG1, indicating that a bead-based multiplex assay using GPI1 in combination with SAG1 may strengthen Toxoplasma gondii serology, in particular in seroepidemiological studies.