Trypanosoma (Nannomonas) congolense: Analysis by Fluorescein-Conjugated Plant Lectins of Surface Saccharides of Cloned Variant Antigen Types Differing in Infectivity for Mice

Abstract

Surface saccharides of 4 cloned VAT (variant antigen types) of T. (Nannomonas) congolense, AmNat (Amherst Nannomonas antigen types) 1.1, 1.2, 2.1 and 3.1, derived from 3 different stocks were compared by fluorescein-conjugated, plant lectins using a quantitative fluorescence method. It was ascertained by the ID63 assay that the 4 AmNat differed in their infectivity for mice. The lectins employed for AmNat 1.1, 2.1, and 3.1 were concanavalin A (Con A), wheat germ agglutinin (WGA), soybean agglutinin (SBA), garden pea agglutinin (GPA), and gorse seed (Ulex europaeus) agglutinin (UEA). In view of the results obtained with these 3 AmNat, only Con A, WGA and GPA were used with AmNat 1.2, which was isolated after the lectin analyses of the other cloned VAT were completed. On the basis of experimental results, the amounts of saccharide residues binding the several lectins differed among the 4 AmNat. In each instance, the reaction specificity was controlled by inclusion of an appropriate sugar in the incubation mixture. Although the actual numbers of various specific lectin-binding sites differed among the AmNat 1.1, 2.1, and 3.1, all of them were found to have the following sugars on their surfaces: .alpha.-D-mannose, N-acetyl-D-glucosamine, D-galactose, .alpha.-D-glucose and .alpha.-L-fucose. AmNat 1.2 treated with Con A, WGA and GPA only had the first 2 sugars named above and .alpha.-D-glucose residues. The results of the ID63 assay indicated AmNat 1.1 and 2.1 to be significantly more infective for mice than AmNat 1.2 and 3.1. The lectin analysis revealed that the 2, more infective, cloned VAT incubated with Con A or WGA emitted significantly (.apprx. 39% to .apprx. 62%) more fluoresence than the less infective ones. There was significantly more numerous Con A and WGA binding sites on the more infective AmNat. The situation was reversed with regard to GPA. Upon treatment with this lectin, fluorescence emitted by AmNat 1.1 and 2.1 was significantly (.apprx. 56% to .apprx. 81%) lower than that recorded for the less infective AmNat 1.2, and 3.1. Infectivity of T. congolense cloned VAT was correlated with the presence of higher numbers of .alpha.-D-mannose and N-acetyl-D-glucosamine residues and of lower numbers of .alpha.-D-glucose residues on the surface of the bloodstream trypanosomes. There appeared to be no correlation between infectivity and the numbers of D-galactose and .alpha.-L-fucose residues present on these parasites.