Purification of a Trypanosoma cruzi membrane glycoprotein which elicits lytic antibodies

Recent studies on the humoral immune response to Trypanosoma cruzi have shown that antibodies which are able to bind living parasites and lyse them in conjunction with complement are associated with host protection. Antibodies which support complement-mediated lysis (CML) of trypomastigotes are elicited as a result of an active infection and not after immunization with killed parasites. In spite of the requirement for immune antibodies, lysis proceeds mainly via the alternative complement pathway. We have purified a 160-kilodalton (kDa) glycoprotein from T. cruzi metacyclic trypomastigotes which appears to be a specific target for lytic antibodies. Rabbit antiserum to the purified 160-kDa protein was prepared, and we have determined that these antibodies will support CML of tissue-culture-derived trypomastigotes. The percentage of killing (65 to 70%) was consistent among three different T. cruzi strains tested. In order to examine the specificity of antibody-dependent CML, antibodies to T. cruzi neuraminidase, an unrelated trypomastigote membrane glycoprotein, were tested in the CML, assays and were not found lytic. Viable trypomastigotes bound anti-160-kDa antibodies uniformly as demonstrated by immunofluorescence, whereas antineuraminidase antibodies were extensively capped. The 160-kDa glycoprotein is specifically produced in infectious trypomastigotes (tissue culture derived and metacyclic) and was not detected in epimastigotes or amastigotes. The identification of the 160-kDa glycoprotein as a specific target for lytic antibodies, as well as its expression only in the infectious stage of the parasite, suggests an important role for this protein in eliciting host immunity.