Characterization of an excreted/secreted antigen form of 14-3-3 protein in Toxoplasma gondii tachyzoites.

The 14-3-3 protein was shown to be present into the parasitophorous vacuole of Toxoplasma gondii-infected human monocyte cells and in the excreted/secreted antigens (ESA). The ESA 14-3-3 protein migrates electrophoretically as the cytosol and the main membranous 14-3-3 isoforms. The excretion/secretion of 14-3-3 was not sensitive to cycloheximide, a protein synthesis inhibitor, even at a concentration which inhibited the production of 14-3-3 inside the tachyzoites. Recombinant 14-3-3/GST protein was used to test the presence of 14-3-3 antibodies in different human sera. A positive immunoreactivity was observed with sera corresponding to acute toxoplasmosis and a possible involvement of 14-3-3 in host immunity is discussed.