A pattern in the development of agglutinogenic antigens of cyclically transmitted isolates of Trypanosoma gambiense.

Three isolates of T. gambiense, belonging to 2 serologically different substrains of the species, were cyclically transmitted to rabbits and monkeys by G. morsitans or G. tachinoides. Sera collected from the infected animals were tested for agglutinating antibodies to 17 different serotype antigens prepared from rodent-adapted isolates of T. gambiense. The first antibodies detected in sera from all of the animals agglutinated the same serotype antigen L2, indicating that it possibly consisted of trypanosomes bearing a basic antigen of T. gambiense. In 2 animals infected with 1 isolate the development of antibody to the common serotype L2 was accompanied by the development of antibody to a second serotype U1. Comparisons of the patterns in which antibodies were produced to other serotype antigens in different animals indicated that there were many similarities in the sequences in which they developed in different rabbits infected with (a) any 1 isolate (b) 2 different isolates of 1 substrain and (c) isolates of 2 serologically different substrains. There were also similarities in the sequences in which the antigens developed in rabbits and monkeys infected with an isolate by the same fly or by different tsetse flies. The ordered sequence in which these 3 cyclically transmitted isolates of T. gambiense, of significantly varied origin and laboratory history, produced variant antigens in hosts of different species provides further evidence to support previous suggestions that antigenic variation in trypanosomes is an adaptive process, rather than one involving selection of mutants.