Expression of two variant surface glycoproteins on individual African trypanosomes during antigen switching.

Individual Trypanosoma brucei rhodesiense organisms were observed in the process of switching variant surface glycoproteins (VSG's). During this switch, trypanosomes simultaneously expressed both pre- and postswitch VSG's uniformly over their surface as detected with monoclonal antibodies. Analysis of this switching event showed that trypanosomes expressing any one of three distinct preswitch VSG's could switch to expression of from one to three different postswitch VSG's. Up to 2.7 percent of the trypanosome population was in the process of switching at one time.