Identification of Toxoplasma gondii SUB1 antigen as a marker for acute infection by use of an innovative evaluation method.

By the separation of Toxoplasma lysate using two-dimensional gel electrophoresis and its analysis with human serum samples and mass spectrometry, the subtilisin-like protein (SUB1) was identified to be a potential marker for acute toxoplasmosis. Following expression of the C-terminal domain of SUB1 in Escherichia coli, it was tested in a line blot assay using a total of 80 human serum samples. Two computer programs based on different evaluation strategies were used for judgment of the line blot results: (i) a time-dependent method with a predefined cutoff value and (ii) a fixed-time-point method with a calculated cutoff. Thereby, SUB1 was proven to be rather reactive with specific immunoglobulin A (IgA), IgM, and IgG of patients with an acute infection. This finding makes this antigen an attractive candidate for improving diagnosis of toxoplasmosis and demonstrates that not only the selection of respective antigens but also the evaluation method chosen are important for the evaluation of new diagnostic markers.