Studies on the Metacyclic Variant Antigen Genes of African Trypanosomes

Devaney, Frances (1986) Studies on the Metacyclic Variant Antigen Genes of African Trypanosomes. MSc(R) thesis, University of Glasgow.

Abstract

Trypsnosomes contain a repertoire of a possible 100-1000 different genes for variant surface glycoproteins (VSGs). A small and strain specific fraction of these genes is expressed in the salivary glands of the tsetse fly giving rise to metacyclic variant antigen types (M-VATs). These M-VATs continue to be expressed up to day nine of infection in the bloodstream of immunosuppressed mice. The variable antigen repertoire expressed by T. b. rhodesiense metacyclics is not influenced by the anamnestic expression whereby the VAT ingested by the fly is present at high levels in early bloodstream populations of fly infected mice. This has been demonstrated by feeding tsetse flies a trypanosome line expressing a VAT, encoded by a single-copy gene which is normally a component of the metacyclic repertoire, GUTat 7.13. This VAT did not constitute a significantly increased proportion of the resultant metacyclic population in the fly, nor was it expressed at higher levels in the bloodstream of fly infected mice. Analysis of trypanosome DNA isolated from fly infected mice revealed that for those trypanosomes expressing GUTat 7.13 a new expression linked copy (ELC) of this gene was made. The presence of this new ELC was directly correlated with the presence of 7.13 expressors. It is concluded that the expression of VSG genes in the fly and in the mammal is controlled by different mechanisms. The distribution of acute sleeping sickness caused by T. b. rhodesiense is not homogeneous throughout East Africa, rather discrete foci of infection exist where the disease is endemic. Trypanosomes with similar VAT repertoires which share predominant VATs (those which tend to appear early in infection) can be grouped into serodemes and individual serodemes are associated with individual foci. Stocks from an endemic focus in the Luangwa Valley, Zambia were cloned and tested for relatedness in antigen repertoire to stocks isolated from an endemic focus in Kenya using serological and DNA analysis. It was concluded that stocks from these two foci in East Africa were members of different serodemes.

• Item Type: Thesis (MSc(R))
• Qualification Level: Masters
• Keywords: Zoology, Parasitology
• Date of Award: 1986
• Depositing User: Enlighten Team
• Unique ID: glathesis:1986-77363
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jan 2020 11:53
• Last Modified: 14 Jan 2020 11:53
• URI: https://theses.gla.ac.uk/id/eprint/77363