Antigenic heterogeneity of metacyclic forms of Trypanosoma brucei

Abstract

AFRICAN trypanosomiasis is a relapsing disease chiefly affecting man and his domestic stock. The infected mammal mounts a protective, trypanolytic immune response to the trypanosome's surface antigen, but a few parasites have already undergone antigenic variation by that time¹. Parasitaemic remissions and recrudescences occur as a seemingly inexhaustible series of surface variable antigen types (VATs) are expressed randomly by the flagellate^2,3. Reversion of the trypanosome population to a ‘basic’ antigen type at the end of its cyclical development in ithe tsetse fly's salivary glands has been suggested^4–6. Prospects of vaccination, and of early serodiagnosis of trypanosomiasis, would be greatly improved by use of such a basic VAT. Specific immunofluorescence and immune lysis tests now make possible the identification of the VAT of individual trypanosomes¹. We have applied these techniques to metacyclic trypanosomes. Our results show that VAT heterogeneity is present in the metacyclic population.