Lectin receptors as markers for Trypanosoma cruzi. Developmental stages and a study of the interaction of wheat germ agglutinin with sialic acid residues on epimastigote cells.

Abstract

T. cruzi at various stages of maturation and differentiation were isolated by conventional cellular fractionation procedures and characterized by cell surface markers using 30 highly purified lectins encompassing all known sugar specificities. Cell surface carbohydrates of the various T. cruzi stages were analyzed by agglutination and lectin-binding assays. Specific receptors for wheat germ agglutinin (WGA), Helix pomatia, Sophora japonica and Bandeiraea simplicifolia lectin II were found only in culture epimastigotes, whereas peanut agglutinin (PNA) sites were present exclusively in amastigotes, those for Phaseolus vulgaris in bloodstream trypomastigotes and amastigotes, and for Wisteria floribunda hemagglutinin predominantly in culture forms of T. cruzi. The N-acetylgalactosamine (DGalNAc)-binding lectin from Bauhinia purpurea agglutinated and inhibited the movement of epimastigotes and bloodstream tryomastigotes, but it only inhibited, without agglutinating, culture trypomastigotes. Because both the agglutination and inhibition of movement were reversed by specific sugar haptens, B. purpurea sites were present in all the flagellated parasites. PNA sites were detectable on epimastigotes after the cells were treated with sialidase, whereas, at the same time, WGA receptors were completely removed and those for the other sialic acid-binding proteins, Aaptos papillata lectin II and Limulus polyphemus, were partially eliminated; moreover, the activity of W. floribunda hemagglutinin, a D-GalNAc-binding lectin, increased 4000 times. Trypsinization and lyzozyme treatment of epimastigote cells did not significantly affect lectin agglutination or lectin binding. WGA reacted solely with sialic acid residues on epimastigote cell surface with an apparent association constant of 2 .times. 106 M-1, each epimastigote having an estimated average of 3 .times. 106 WGA sites, as determined by binding experiments and a minimum of 7.7 .times. 106 sialic acid residues, as calculated by colorimetric method after sialidase digestion. Evidences are presented that the sialyl residues are rapidly regenerated (in .apprx. 4 h) and that they, at least for the most part, are not adsorbed from the culture medium. The receptor for the D-mannose-binding lectins (concanavalin A [Con A] and Lens culinaris) must either be on the same carbohydrate moiety having the WGA site, or, if in a distinct molecule, both carrier molecules of Con A and WGA sites must be located close to each other in the plasma membrane of the parasite.