A species-specific antigen of Trypanosoma (Duttonella) vivax detectable in the course of infection is encoded by a differentially expressed tandemly reiterated gene.

A monoclonal antibody that is used as a Trypanosoma vivax species-specific diagnostic reagent on antigen-trapping enzyme-linked immunosorbent assay recognized an 8-kDa peptide on western blots. The 8-kDa species-specific antigen was isolated and employed in raising rabbit polyclonal antibodies, which were used in the immunoscreening of a T. vivax cDNA library in lambda gt11.2. A clone containing a 0.8-kb insert was isolated. The cloned gene is tandemly repeated, with a monomeric unit length of 900 bp, in the genomes of all T. vivax isolates from diverse geographic locations in Africa and South America. The gene is differentially expressed, since both the transcript and antigen are present in bloodstream-stage parasites, but not in the epimastigotes of T. vivax. Although the gene is found in all T. vivax isolates so far tested, it either exists in low copy number or in a divergent form in one isolate from Kilifi at the Kenya Coast. Sequence translation revealed a remarkable degree of bias in codon usage with preference for G and C (82%) in the wobble position. Using the deduced amino acid sequence to search the databases for any structurally related peptides, revealed no significant identity with any known proteins. The function of the species-specific antigen of T. vivax is thus unknown. Nevertheless the identification and characterization of proteins released into the circulation of protozoan parasite-infected animals is important and should allow the determination of what role such molecules may play in the modulation of disease pathology.