CROSS-REACTIVITY STUDIES AND DIFFERENTIAL SERODIAGNOSIS OF HUMAN INFECTIONS CAUSED BY TRYPANOSOMA-CRUZI AND LEISHMANIA SPP - USE OF IMMUNOBLOTTING AND ELISA WITH A PURIFIED ANTIGEN (AG163B6)

Results of our studies on the reactivity of chagasic and leishmaniasic sera with the purified T. cruzi-specific antigen 163B6, as assessed b y ELISA, and with complex antigenic mixtures from T. cruzi and Leishma nia mexicana, by immunoblotting, are presented here. Our objective was to identify the antigens responsible for the exhibited cross-reactivi ty between trypanosomiasis and leishmaniasis, and to find a specific r eactivity pattern corresponding to each parasitosis. In spite of the h igh cross-reactivity observed with the immunoblotting, the use of 7.5% A-B gels made it possible to identify a characteristic pattern for ea ch parasitosis, that could be distinguished by the naked eye. The char acteristic pattern corresponding to chagasic patients was ascribed to reactivity with T. cruzi bands of mel, wts 131, 125, 116, 111, 51-45 a nd 43 kD, that were not recognized by leishmaniasic sera. Trypanosoma cruzi antigens of mol. wts 85, 81, 70, 65-60, 37 and 32 kD were consid ered as crossing antigens, since they were recognized by leishmaniasis sera. With L. mexicana, most of the chagasic patients presented react ion with antigen of mol. wts 124, 107, 92, 59 and 32kD, while bands of mol. wts 155, 140, 73, 56 and 48 kD were recognized only by leishmani asic sera. In this study we found 12 out of 45 sera of patients with l eishmaniasis, from a region endemic for both parasitoses, which exhibi ted a pattern of bands very similar to those corresponding to chagasic individuals, strongly suggesting a mixed infection. This hypothesis w as verified by using a purified specific antigen of T. cruzi, Ag163B6, which would be the major cysteine proteinase of this specie (cruzipai n). By ELISA, these 12 sera showed a positive reaction with this purif ied antigen, as those of chagasic patients, thus leading to the confir mation of the presence of a mixed infection.