Characterization of Soluble and Membrane-Bound Proteins of Toxoplasma gondii as Diagnostic Markers of Infection

Imen Khammari, Sami Lakhal, Benoît Westermann, Alia Benkahla, Aïda Bouratbine, Alain Van Dorsselaer, Moncef Ben Saïd, Christine Schaeffer-Reiss and Fatma Saghrouni

In the present study, we applied the combination of one-dimensional gel electrophoresis, immunoblot and nanoliquid chromatography-tandem mass spectrometry (nanoLC-MS/MS) to identify potential immunogenic proteins of Toxoplasma gondii tachyzoites that can be used for the development of reliable assays in the serodiagnosis of acquired toxoplasmosis in immunocompetent subjects. For this purpose, we developed an immunoblot using soluble and membrane extracts of GT1 Toxoplasma gondii tachyzoites and tested 194 positive and 100 negative sera obtained from pregnant women.

Five bands of soluble antigens (98 kDa, 36 kDa, 33 kDa, 32 kDa and 21 kDa) and 4 bands of membrane antigens (41 kDa, 35 kDa, 32 kDa and 30 kDa) were selected as the most valuable in terms of sensitivity and specificity. Among these bands, only 2 bands of soluble antigen (33 kDa and 32 kDa) and 2 bands of membrane antigen (32 kDa and 30 kDa) showed a specificity ≥ 90%.

After mass spectrometry and bioinformatics analysis, 7 proteins were identified as potential markers for serodiagnosis of toxoplasmosis. These proteins are: SRS34A, GRA7, GRA1, DG32, MIC5, ROP5 and Toxofilin. These proteins showed a 86% to 100% homology with proteins of both VEG and ME49 strains of T. gondii and a 58% to 87% homology with Hammondia hammondi; and can be considered as attractive candidates for the development of an immunochromatography test that can be used for the rapid diagnosis of toxoplasmosis and as a confirmatory test when routine techniques give equivocal results.