Identification of antigenic proteins of Toxoplasma gondii RH strain recognized by human immunoglobulin G using immunoproteomics.

Toxoplasma gondii, a ubiquitous intracellular protozoan, infects one third of the world human population. It is of great medical significance, especially for pregnant women and immune-compromised patients. Accurate and early detection of T. gondii infection is crucial in the management of this disease. To obtain potential diagnostic markers, immunoproteomics was employed to identify immunodominant proteins separated by 2-D immunobloting and probed with sera collected from Toxoplasma-positive pregnant women. MALDI-TOF MS and MS/MS analyses identified a total of 18 immunoreactive proteins that were recognized by Toxoplasma-positive sera, whereas none was reactive with the negative-control sera from healthy, Toxoplasma-negative volunteers. Pregnant women showed a diverse immunoreactivity pattern with each serum recognizing one to eight identified tachyzoite proteins. The identified proteins were localized in the membrane, cytoplasm and specific organelles of T. gondii, and are involved in host cell invasion, metabolism and cell structure. Among these 18 proteins, actin, catalase, GAPDH, and three hypothetical proteins had a broad reactivity with Toxoplasma-positive sera, indicating their potential as diagnostic markers for toxoplasmosis. Each of several combinations of the identified proteins offered 100% detection of Toxoplasma infections of all 28 Toxoplasma-positive women. The study findings suggest that Toxoplasma tachyzoites are highly immunogenic and highlights the heterogeneity of host responses to Toxoplasma infection and the importance of using combinations of immunogens as diagnostic antigens. The findings have significant implications to the development of diagnostic reagents with high sensitivity and specificity.