Isolation and characterization of a Trypanosoma Congolense gene encoding an antigen recognised by infection serum from Cape Buffalo

Abstract

Three members of the Salivarian trypanosomes, namely, Trypanosoma vivax, T congolense and T brucei brucei, cause African animal trypanosomosis. In the . attempt to arrive at an effective vaccine, research has focused on identifying trypanosome antigens that would elicit imrnunoprotection. Variant surface glycoproteins, (VSGs), the predominant proteins forming the 12-15 nm thick surface coat of the parasites, are strong immunogens, but are ineffectual as components of a vaccine since they are hyper-variable and alter through a process termed antigenic variation. More attention is consequently being given to antigens that are non-variant or that have a significantly reduced capacity to vary. Certain domestic and wild animals such as the African Cape Buffalo (Synercus caffer) display a level of resistance to the disease (trypanotolerance). Part of the mechanism of trypanotolerance may be attributed tothe ability of these ungulates to raise antibodies against vital trypanosome antigens. In this study, serum from trypanosome-infected Buffalo was used to screen T congolense cDNA and genomic DNA expression libraries with the aim of identifying genes encoding non-variant antigens recognised during an infection to determine whether these constitute vaccine candidate antigens. A variety of techniques were employed to purify and characterise selected clones of interest. These included: nucleic acid preparation, PCR amplification, restriction enzyme analysis, agarose gel electrophoresis, Southern and Northern analyses and sequencing. A VSG-like gene was identified and cloned for characterisation by sequencing. Southern analysis showed that this gene occurs as a single copy within

the T congolense IL 3000 and IL 1180 genomes. In addition, through Northern

analysis, it was determined that it is expressed in both the metacyclic and bloodstream stages of the parasite. It was observed that the putative protein encoded by this gene is similar to 117, an invariant T brucei flagellar antigen with noted diagnostic potential. Based on preliminary evidence of its invariance and immunogenicity, the putative protein may hold potential as a candidate vaccine antigen. Further work should be done to determine the cellular localisation of the putative protein as well as its protective potential.