Independent expression of the metacyclic and bloodstream variable antigen repertoires of Trypanosoma brucei rhodesiense.

The variable antigen repertoire expressed by metacyclic Trypanosoma brucei rhodesiense is not influenced by the anamnestic expression whereby the variable antigen type (VAT) ingested by a tsetse fly is present at high levels in early bloodstream populations of fly-infected mice. This has been demonstrated by feeding to Glossina morsitans a trypanosome line expressing a VAT which is normally a component of the metacyclic repertoire. The VAT did not constitute a significantly increased proportion of the resultant metacyclic population which would have occurred had anamnestic expression and metacyclic expression been linked. Five other metacyclic VATs were also present at control levels. We conclude that the mechanisms of expression of VATs in the fly and in the mammal are independently controlled.