[African trypanosomes: parasites with protective mechanisms].

African trypanosomes have developed protective mechanisms in order to escape from their hosts' immune attack. New cell surface antigens become sequentially expressed during a chronic infection providing the parasites continuously with immunologically altered faces. The trypanosomal genome contains a considerable repertoire of different genes coding for the surface antigens; they become separately activated and expressed by a variety of novel molecular processes. In addition, the trypanosomal cell surface participates in the protection of the parasites against non-immune defense mechanisms of the host.