Biochemistry of the Variant Surface Glycoproteins of Salivarian Trypanosomes

Abstract

This chapter describes the progress made over the past years in characterizing antigens of the principal pathogenic salivarian trypanosomes. Although bulk of information comes from work on the variant antigens of T. b. brucei in particular, much interesting work has been done on the variant antigens of other species and is discussed in the chapter. Future perspectives for immunoprophylaxis, serodiagnosis, or chemotherapy of trypanosome infections are also presented. The mammalian trypanosomes have been divided into seven subgenera that are grouped into two sections based on the site of the production of infective metacyclic trypanosomes in the invertebrate host. The subgenera are Trypanosoma brucei brucei , Trypanosoma brucei gambiense , Trypanosoma brucei rhodesiense , Trypanosoma evansi , Trypanosoma equiperdum Trypanosoma ( Nannomonas ) congolense , and Trypanosoma ( Duttonella ) vivax . The chapter presents the systematic position of the genus Trypanosoma and the seven subgenera that infect mammals and summarizes the main features of each subgenus. Antigenic variation in the mammalian host is the most striking characteristic of salivarian trypanosomes. Variant surface glycoproteins (VSGs) are synthesized with a hydrophobic C-terminus absent from purified VSG. Little work has been done on the biochemistry of antigens expressed by metacyclic trypanosomes of any species, because the amount of material available is limited. There is interest in the antigenic composition of metacyclic trypanosomes because if the repertoire is restricted, vaccination could be a possibility. The serological evidence suggests that the repertoire of metacyclic variant antigen types (VATS) is restricted, and there is limited overlap between VATS present in metacyclic and in bloodstream populations.