Use of Toxoplasma Gondii Recombinant Antigens for Diagnosis and Seroepidemiology

Abstract

The production of antigens for serological tests used in the diagnosis of infections with T. gondii has been complicated by the fact that the T. gondii life cycle stages from which these antigens are derived are obligately intracellular. Therefore, traditional antigen preparations, which are usually derived from parasites grown in tissue cultures or the peritoneal cavities of mice, are inevitably contaminated with at least some host material. In addition, such antigen preparations are expensive and lack standardization. In an attempt to overcome these problems, we have cloned, sequenced and characterized fragments of two single-copy genes, termed H4 and H11, that encode antigenic polypeptides of T. gondii [Johnson and Illana, 1991]. The messenger RNAs of the H4 and H11 genes consist of about 1300 and 1900 nt, respectively, and occur in low abundances in the endozoite stage of T. gondii. The native endozoite polypeptides encoded by the H4 and H11 genes have apparent molecular weights of 25000 and 41000, respectively. To examine the diagnostic potential of the recombinant H4 and Hll polypeptides the H4 and H11 gene fragments were subcloned from a Lambda gt11 expression library into the plasmid pGEX-lN. The recombinant polypeptides were then expressed as glutathione-S-transferase fusion polypeptides [Tenter and Johnson, 1991] and used to develop Enzyme-linked Immunosorbent Assays (ELISAs) for diagnosis of T. gondii infections in intermediate and definitive host.