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Although several hundred of different antigen genes exist in the trypanosome genome, only one is usually expressed at a time. This expression occurs in one of several possible telomeric expression sites. Besides being exclusively telomeric, transcription of the antigen gene exhibits other particular characteristics: the RNA polymerase is highly resistant to alpha-amanitin, and the transcription unit comprises several other genes, one of which may encode an adenylate cyclase. Post-transcriptional controls modulate the activity of this transcription unit during the parasite life-cycle. Antigenic variation is achieved through either alternative activation of different expression sites, or gene recombination within a given expression site. These mechanisms ensure a relative programming of antigen expression.

M/S n° 10, vol. 24, octobre 2008 > Les trypanosomes africains (prototype Trypanosoma brucei) sont des protozoaires flagelles capables d’infecter de nombreux mammiferes. Chez l’homme, ces parasites provoquent la maladie du sommeil, fatale si elle n’est pas traitee precocement. Des 1900, Laveran et Mesnil notent qu’en fait l’homme est immun contre T. b. brucei, et que seules des formes variantes derivees de cet organisme, maintenant appelees T. b. rhodesiense et T. b. gambiense, sont capables d’echapper a notre defense innee [1].