Antigenic variation is a mechanism exploited by parasitic protozoa to evade the host's immune response. Studies on such variation are of cardinal importance in approaching the practical problems of vaccine design and diagnosis of infection by serological tests. Coincidently these studies have revealed novel gene expression mechanisms which are of fundamental biological interest (Vickerman and Barry, 1982). The African (salivarian) trypanosomes all exhibit antigenic variation and the process has been studied in Trypanosoma brucei subspecies in particular.
