A SPECIES-SPECIFIC ANTIGEN OF TRYPANOSOMA (DUTTONELLA) VIVAX DETECTABLE IN THE COURSE OF INFECTION IS ENCODED BY A DIFFERENTIALLY EXPRESSEDTANDEMLY REITERATED GENE

A monoclonal antibody that is used as a Trypanosoma vivax species-spec ific diagnostic reagent on antigen-trapping enzyme-linked immunosorben t assay recognized an 8-kDa peptide on western blots. The 8-kDa specie s-specific antigen was isolated and employed in raising rabbit polyclo nal antibodies, which were used in the immunoscreening of a T. vivax c DNA library in lambda gt11.2. A clone containing a 0.8-kb insert was i solated. The cloned gene is tandemly repeated, with a monomeric unit l ength of 900 bp, in the genomes of all T. vivax isolates from diverse geographic locations in Africa and South America. The gene is differen tially 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, i t either exists in low copy number or in a divergent form in one isola te from Kilifi at the Kenya Coast. Sequence translation revealed a rem arkable degree of bias in codon usage with preference for G and C (82% ) in the wobble position. Using the deduced amino acid sequence to sea rch the databases for any structurally related peptides, revealed no s ignificant identity with any known proteins. The function of the speci es-specific antigen of T. vivax is thus unknown. Nevertheless the iden tification and characterization of proteins released into the circulat ion of protozoan parasite-infected animals is important and should all ow the determination of what role such molecules may play in the modul ation of disease pathology.