Abstract
Salivarian trypanosomes sequentially express only one variant surface glycoprotein (VSG) on their cell surface from a large repertoire of VSG genes. Seven cryopreserved animal trypanosome isolates known as TeAp-ElFrio01, TEVA1 (or TeAp-N/D1), TeGu-N/D1, TeAp-Mantecal01, TeGu-TerecayTrino, TeGu-Terecay03 and TeGu-Terecay323, which had been isolated from different hosts identified in several geographical areas of Venezuela were expanded using adult albino rats. Soluble forms of predominant VSGs expressed during the early infection stages were purified and corresponded to concanavalin A-binding proteins with molecular masses of 48–67kDa by sodium dodecyl sulfate-polyacrylamide gel electropohoresis, and pI values between 6.1 and 7.5. The biochemical characterization of all purified soluble VSGs revealed that they were dimers in their native form and represented different gene products. Sequencing of some of these proteins yielded peptides homologous to VSGs from Trypanosoma (Trypanozoon) brucei and Trypanosoma (Trypanozoon) evansi and established that they most likely are mosaics generated by homologous recombination. Western blot analysis showed that all purified VSGs were cross-reacting antigens that were recognized by sera from animals infected with either T. evansi or Trypanosoma (Dutonella) vivax. The VSG glycosyl-phosphatidylinositol cross-reacting determinant epitope was only partially responsible for the cross-reactivity of the purified proteins, and antibodies appeared to recognize cross-reacting conformational epitopes from the various soluble VSGs. ELISA experiments were performed using infected bovine sera collected from cattle in a Venezuelan trypanosome-endemic area. In particular, soluble VSGs from two trypanosome isolates, TeGu-N/D1 and TeGu-TeracayTrino, were recognized by 93.38% and 73.55% of naturally T. vivax-infected bovine sera, respectively. However, approximately 70% of the sera samples did not recognize all seven purified proteins. Hence, the use of a combination of various VSGs for the diagnosis of animal trypanosomosis is recommended.
Highlights
Salivarian trypanosomes have a dense surface coat composed predominantly of a unique type of variant surface glycoproteins (VSG), which shields the invariant surface proteins from host immune system effectors and prevents complement activation (Turner et al, 1985)
We have focused on the diagnosis of T. vivax-caused animal trypanosomosis by using cross-reacting antigens isolated from other trypanosomes (Uzcanga et al, 2002, 2004; Camargo et al, 2004; Velásquez et al, 2014)
We investigated the potential use of VSG variants as diagnostic reagents for the detection of trypanosomosis caused by T. vivax and T. evansi, and examined whether the soluble form of these VSG antigens contained common epitopes recognized by sera from animals infected with either of these species of trypanosomes
Summary
Salivarian trypanosomes have a dense surface coat composed predominantly of a unique type of variant surface glycoproteins (VSG), which shields the invariant surface proteins from host immune system effectors and prevents complement activation (Turner et al, 1985). VSG itself is highly immunogenic and elicits specific trypanocidal responses from the host’s immune system. Trypanosomes escape this immune response by switching their dense protective VSG coat. A high host antibody titer to a particular VSG causes clearance of trypanosomes expressing that particular VSG. Trypanosomes that switch VSG expand as a new population until they in turn are recognized by the host immune system. Trypanosomes persist in their mammal hosts due to their antigenic variation strategy (Barry and McCulloch, 2001; Taylor and Rudenko, 2006; Jackson et al, 2012)
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