Nonvariant Antigens Limited to Bloodstream Forms of Trypanosoma brucei brucei and Trypanosoma brucei rhodesiense1

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Abstract
The presence of nonvariant antigens (NVA) limited to bloodstream forms of T. b. brucei and T. b. rhodesiense was demonstrated for the 1st time by immunodiffusion and immunoelectrophoresis. Noncloned and cloned populations were employed in preparation of polyclonal antisera in rabbits and of antigens to be used in the immunologic reactions. The NVA could be shown best in systems in which hyperimmune rabbit sera (adsorbed with procyclic forms to eliminate antibodies against antigens common to bloodstream form and procyclic stages) were reacted with trypanosomes characterized by heterologous variant-specific antigens (VSA). The NVA demonstrated in this study are very likely different from the common parts of VSA. As has been suggested by experiments with living trypanosomes, at least a part of the NVA appears to be located on the surface of the bloodstream forms. In these experiments involving the quantitative indirect fluorescent antibody test, the amount of fluorescence recorded for the heterologous system, i.e., ETat 5 trypanosomes incubated with anti-AmTat 1.1 serum, equalled .apprx. 3.0% of the fluorescence emitted by the AmTat 1.1 bloodstream forms treated with their homologous antiserum. Evidently, only small amounts of NVA are present on the surfaces of T. brucei bloodstream forms. In addition to the NVA, the electrophoresis results suggested the presence of antigenic differences between procyclic stages belonging to different T. brucei stocks.