Antigenic variation in trypanosomes

Abstract

The several species of African trypanosomes pathogenic to man and domestic livestock may evade the immune response through a process of antigenic variation. This phenomenon is the major obstacle to immunization. Variation may be recognized in the form of sequential changes in the serological characteristics of the trypanosome surface during the course of an infection. Each serological variant of Trypanosoma brucei possesses a unique glycoprotein covering the entire trypanosome surface. When an immune response occurs against the prevailing variant, the trypanosomes are able to express an alternative and immunologically distinct glycoprotein. The antigenic repertoire of a trypanosome clone or species is so far undetermined and the genetic basis of antigenic variation is unexplored. Structural studies indicate that the immunological uniqueness of each glycoprotein is due primarily to immense variations in amino acid sequence distributed throughout the single polypeptide backbone. The extent of glycosylation is also variable.