Development of recombinant TgsGP antigen for serodiagnosis of trypanosoma brucel gambiense

Abstract

The majority of human African trypanosomiasis (HAT) cases are caused by Trypanosoma brucei gambiense (T.b. gambiense). This parasite is transmitted by tsese flies and is endemic in rural settings of West and Central Africa. The parasite can infect man because it can resist lysis by the human serum through expression of the T.b. gambiense specific glycoprotein (TgsGP). Different diagnostic tools have been developed for T.b. gambiense HAT. Among the serological tests, detecting antibodies against T.b. gambiense, the CATT/T.b. gambiense is used for mass screening in endemic areas. Recently, a rapid diagnostic test in dipstick format has been developed for T.b. gambiense HAT. However, both tests are based on native LiTat 1.3 and/or LiTat 1.5 antigens. However, not all T.b. gambiense strains do express these immunodominant VSGs leading to lower sensitivities in certain areas. In my thesis work, I have developed an in vitro system for the recombinant expression of the T.b. gambiense specific TgsGP protein and evaluated its diagnostic potential in ELISA with sera from HAT patients and controls. Advances in developing recombinant antigens will lead to increased performance and affordability of serodiagnostic tests for T.b. gambiense HAT. The recombinant TgsGP (rTgsGP) was successfully expressed in Origami E. coli cells and purified in a two-steps approach, affinity chromatography followed by size-exclusion chromatography. Purified rTgsGP antigen was first tested in western blot strips with 7 HAT patients’ sera and 5 controls. The diagnostic accuracy of the rTgsGP antigen was evaluated by ELISA with sera from 100 T.b. gambiense patients, 50 T.b. gambiense-endemic negative controls, 78 T.b. rhodesiense patients and 50 T.b. rhodesiense-endemic negative controls. Based on the ELISA OD values, the area under the receiver operator characteristics curve (AUC) was calculated at 0.86. This indicates a good diagnostic accuracy. However, native as well as recombinant LiTat 1.3 and 1.5 antigens showed higher AUC values (>0.95) in previous studies, and may thus be better antigens for the diagnosis of T.b. gambiense HAT.