Synthesis and Characterization of Latex-protein Complexes from Different Antigens of Toxoplasma gondii for Immunoagglutination Assays

Abstract

The acute phase recombinant protein of Toxoplasma gondii P22Ag was expressed and purified and thehomogenate of the parasite was obtained from an infected mouse. These antigens were used to producelatex-protein complexes (LPC) through physical adsorption and chemical coupling onto different latexes,with the aim of producing immunoagglutination (IA) reagents able to detect recently acquiredtoxoplasmosis. Polystyrene and ?core-shell? latexes where employed, exhibiting varied particle size,functionality (carboxyl or epoxy), and charge density. In sensitization experiments for producing LPC, therecombinant protein showed better coupling efficiency onto the particles surface than the homogenateand this could be explained by the complex mixture of the homogenate, which includes a large numberof proteins of different molecular mass, isoelectric points, and hydrophobicity. The synthesized LPC wereemployed in IA assays. To this effect, the agglutination reaction was followed by measuring the changesin the optical absorbance by turbidimetry. Experiments against control sera were performed to evaluatethe performance of various LPC and it was observed that the IA test based on P22Ag and thecarboxylated latex of 350 nm of particle diameter allowed a good discrimination between acute sera andchronic/negative ones. The proposed test is cheap, rapid, and easy to implement.