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Analysis of antigen switching rates in Trypanosoma brucei

Published online by Cambridge University Press:  06 April 2009

Gretel S. Lamont ,
R. S. Tucker  and
G. A. M. Cross
Gretel S. Lamont
Affiliation:
Rockefeller University, 1230 York Avenue, New York, NY 10021-6399, USA
R. S. Tucker
Affiliation:
500 East 63rd Street, New York, NY 10021, USA
G. A. M. Cross
Affiliation:
Rockefeller University, 1230 York Avenue, New York, NY 10021-6399, USA
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Summary

Previously quoted figures for the frequency of antigen switching in Trypanosoma brucei are based on incorrect assumptions. In order to determine the correct switching frequency, an equation was derived that takes the growth rates of the newly expressed antigen types into consideration as well as the proportion of switched trypanosomes and the number of generations since the population was antigenically homogeneous. When this equation was applied to published in vitro data, variable values were obtained for the switching frequency in clonal populations originally expressing one antigen type. The calculated most likely switching frequencies ranged from 1·4×10−7 to 3·5×10−6. This variation was probably caused by differences in the growth rates of the new antigen types in the population and failure to detect slow growing variants. To overcome these problems, an experimental procedure was developed to analyse the switching frequency in vitro. Trypanosomes were cloned and grown in parallel cultures. After an appropriate number of generations, cells expressing the original antigen type were destroyed and, from the proportion of cultures that contained new antigen types, the switching frequency was calculated. The technique minimized subculturing or other procedures that could distort the results. Although the method was optimized for analysing switching frequency, the values differed between experiments, ranging from 2·2×10−7 to 2·6×10−6 for one variant. Possible causes for the variations in switching frequency are discussed.

Type
Research Article
Information
Parasitology , Volume 92 , Issue 2 , April 1986 , pp. 355 - 367
Copyright
Copyright © Cambridge University Press 1986

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