A radiometric assay for diagnosing lytic antibodies in Trypanosoma cruzi infection

Infective forms of Trypanosoma cruzi were used to evaluate the complement-mediated lysis (CoML) of the parasites in the presence of anti-T. cruzi sera. Parasites released to the supernatant from infected Vero cell monolayers were used. Cultures of 1–3×10⁶ parasites/ml were incubated for 24 h in the presence of 10 Ci/ml of ³H-uridine. Under these conditions 10⁵ parasites used for each determination incorporated about 9600 dpm of the radioactive material. The release of tritium from labelled parasites after incubation with antiserum and complement correlated with the percentage of lysed parasites evaluated by optical microscopy. Normal sera from humans, a guinea pig, a rabbit, and mice were tested as complement sources. Only human sera were suitable for the evaluation of CoML in the presence of antisera, and the levels of lysis attained depended on the serum donor.