Identification and isolation of Trypanosoma cruzi trypomastigote cell surface protein with properties expected of a fibronectin receptor.

The fibronectin receptor of Trypanosoma cruzi trypomastigotes was identified using immunoprecipitation procedure. Parasite radioiodinated surface material was incubated with fibronectin followed by rabbit IgG anti-fibronectin and protein A-Sepharose. The precipitates were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Two radioactive bands were seen. One of 220 kDa corresponded to a subunit of fibronectin molecule present on the parasite surface at the time of isolation. The major radioactive band of 85 kDa corresponded to the fibronectin receptor. Fibronectin receptor was purified using affinity chromatography on human fibronectin coupled to Sepharose. Analysis of fibronectin receptor by sodium dodecyl sulfate-polyacrylamide gels demonstrated one major band of 85 kDa. The purified fibronectin receptor was active since 40-60% of labeled receptor could rebind to fibronectin-Sepharose. In addition, fibronectin receptor could interact with cells bearing fibronectin molecules as shown by the binding of 125I-labeled fibronectin receptor to human monocytes and neutrophils as well as cloned 3T3 fibroblasts. The binding could be inhibited by treatment of cells with anti-fibronectin antibodies. Finally, we showed that the affinity-purified fibronectin receptor and antibodies to the receptor exerted an inhibitory effect on the infection of 3T3 fibroblasts by T. cruzi trypomastigotes in an in vitro culture system.