Identification of chimeric trans-sialidases. Detection of chimeric trans-sialidases in Western blot was performed with antisera raised in mice against each repetitive T. cruzi antigen expressed in pGEX vector. The monoclonal antibody against SAPA-repeats used to probe TS-3R, TS-8R, and TS-13R proteins has been already described.25 The presence of additional immunoreactive bands in TS-Ag 36 protein is due to partial protein degradation. The increase in the apparent molecular weight of TS-Ag 13 protein is attributed to abnormal migration in SDS-PAGE. Molecular weight markers are indicated in kD.