Effect of specific chemotherapy on the levels of lytic antibodies in Chagas's disease.

Clinical trials with compounds active in Chagas's disease have shown that after treatment parasitological diagnostic methods (xenodiagnosis) become repeatedly negative whereas conventional serology (immunofluorescence and complement fixation tests) persists steadily positive. Consequently, assessment of cure still remains controversial. This paper reports the influence of specific treatment on antibodies involved in the conventional serological diagnosis and on antibodies which bind to the living bloodstream forms and are related to host resistance. Antibodies lytic to Trypanosoma cruzi bloodstream stages were detected, through a complement-mediated lysis (CML) test, in: (a) 100% of 28 untreated patients; (b) 94% of a group of 21 treated patients in whom conventional serology remained positive, including those with persistently negative xenodiagnosis; (c) 0% of 17 normal controls. In some patients treated with a nitrofuran derivative (nifurtimox) or with a 2-nitroimidazole derivative (benznidazol), CML test became gradually negative whereas conventional serology continued to be positive. Finally, in five patients treated with benznidazol, serological tests, CML and xenodiagnosis became regularly negative, strongly suggesting parasitological cure. Those findings demonstrate a dissociation between the antibodies mediating serological diagnosis and those directed against living bloodstream parasites. Moreover, since in some patients both types of antibodies disappeared after treatment, the results suggest that cure of Chagas's disease should be based not only on negative xenodiagnosis but also on the elimination of specific antibodies detectable by conventional serology and CML test.