Antigenic variation in African trypanosomiasis: a memorandum.

ABSTRACT

After reviewing the present knowledge on antigenic variation of the trypanosomes of the Trypanosoma (Trypanozoon) brucei species, this Memorandum discusses the relevance of this phenomenon to the possible development of new tools for trypanosomiasis control.As antigenic variation is related to protective immunity and immunopathology, it is of crucial importance for the feasibility of vaccine development and for treatment principles. It is also of interest as a model for understanding antigenic variation occurring during infections with Plasmodium knowlesi, Babesia, and others. Recent methods will permit in depth studies on the antigenic repertoire, the significance of basic antigens, and on the homogeneity of trypanosome populations. For epidemiological purposes, characteristic patterns of variation can be used for strain typing.As regards the basic mechanism of variation, a better insight is required on the molecular structure of the variant antigens. Various methods have so far indicated that they are glycoproteins with a long polypetide chain with 600 amino acids and 15-30 monosaccharide units.The process of variation may be generated by pre-existing genetic information, recombination, or mutation.The stimulus to change variants probably derives, directly or indirectly, from the host immune response, but may also be associated with other environmental factors.The possible relation to acquired resistance, innate immunity, and host specificity, as well as the differences in severity of infection occurring amongst the same host species, are outlined. Histopathological and serological findings are considered in the light of the effect antigenic variation may have on the development of immunopathological lesions.A series of recommendations is included.