The Immunoglobulin (Ig) binding capacity of Toxoplasma gondii tachyzoites was investigated using fluorescence flow-cytometry analysis. Polyclonal mouse, human and rat immunoglobulins without specific anti-Toxoplasma activity bound to parasites in a concentration-dependent manner, saturating them at circulating serum concentrations. The immunoglobulin class and subclass specificity of binding was investigated using irrelevant monoclonal antibodies. IgM, IgA and IgG reacted with the parasite membrane. The attachment of mouse IgM to the parasite surface was hampered by mouse IgG1, IgG2a, IgG2b and IgG3. The binding of mouse IgG was proportionally reduced with increasing concentrations of mouse monoclonal IgM. The binding of murine immunoglobulin was diminished when in presence of human IgG. Purified Fc- but not Fab portions of immunoglobulins, fixed to parasites. Using labelled calibrated beads, the Ig binding capacity of parasites was estimated to be 6900 +/- 500 sites per tachyzoite. The Kd of the T. gondii Fc Receptor (FcR) activity was determined at 1.4 +/- 0.1 microM (mean +/- SEM). Such FcR activity was reduced by phospholipase C, trypsin and pronase treatment of the parasites. These data show a low affinity FcR activity on T. gondii tachyzoites which recognizes Ig of different species and isotypes and is likely supported by a glycosyl-phosphatidylinositol (GPI)-anchored surface protein of the parasite.
Background COVID-19 pandemic is a massive global health emergency. Although RT-PCR is the gold standard for diagnosing suspected cases, there is a need of serological tests to investigate antibody responses. Many serologic immunoassays have been developed to detect antibodies to SARS-CoV2, including rapid tests. This study assessed the clinical performance of the SARS-CoV-2 antibody test (colloidal gold immunochromatography, LEPU TECHNOLOGY) and evaluated the kinetic antibody response in COVID-19 patients.Methods: Samples collected by finger stick; obtained from RT-PCR confirmed cases and samples of negative controls were tested with the IgM/IgG Detection Kit . Results: The kit shows a clinical sensitivity of 65.7 % [59.7%-71.3%] and a specificity of 96.3% [93.0%-98.3%]. The predictive positive value and negative predictive value were respectively 95.2% [91.0%-97.8%] and 71.4% [66.1%-76.2%]. The seroconversion of specific IgM and IgG antibodies were observed as early as the 2nd day after symptom onset.Conclusions: This test is quite useful for assessing previous virus exposure, although negative results may be unreliable during the first weeks after infection. Longitudinal studies on antibody responses during and post infection are needed.
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