[Antigenic variation and the problem of vaccines against African trypanosomes]

African trypanosomes evade the immune response of their host through continuous changes of their major surface antigen, the VSG. This antigenic variation is achieved by either alternative activation of different expression sites for the VSG gene, or DNA rearrangements occurring within a given site. Several minor but invariant surface proteins have recently been characterized. This is especially the case for some surface receptors, which appear to be located in an invagination of the plasma membrane termed the flagellar pocket. These proteins may represent useful targets for new vaccination strategies.