Determination of the specificity of monoclonal antibodies against Schistosoma mansoni CAA glycoprotein antigen using neoglycoconjugate variants

Abstract

The immunogenic O-glycan of circulating anodic antigen (CAA) is a high-molecular-mass polysaccharide with the unique →6)-[β-D-GlcpA-(1→3)]-β-D-GalpNAc-(1→ repeating unit. To obtain information at the molecular level about the specificity of monoclonal antibodies against CAA, the immunoreactivity of two series of bovine serum albumin-coupled synthetic oligosaccharides related to the CAA O-glycan was monitored using ELISA and surface plasmon resonance spectroscopy. The importance of the axial hydroxyl group of β-D-GalpNAc for antibody binding was investigated using the following series of analogues: β-D-GlcpA-(1→3)-β-D-GlcpNAc-(1→O); β-D-GlcpNAc-(1→6)-[β-D-GlcpA- (1→3)]-β-D-GlcpNAc-(1→O); and β-D-GlcpA-(1→3)-β-D-GlcpNAc-(1→6)-[β-D-GlcpA- (1→3)]-β-D-GlcpNAc-(1→O). In the second series of analogues, β-D-Glcp6S-(1→3)-β-D-GalpNAc-(1→O), β-D-GalpNAc-(1→6)-[β-D-Glcp6S-(1→3)]- β-DGalpNAc-(1→O), and β-D-Glcp6S-(1→3)- β-D-GalpNAc-(1→6)-[β-D-Glcp6S-(1→3)]-β-D- GalpNAc-(1→O), the native β-D-GlcpA moiety was replaced by β-D-Glcp6S to evaluate the influence of the nature of the charge on antibody recognition. Comparison of the immunoreactivity of these series with that measured for conjugates containing corresponding synthetic CAA fragments showed that the antibody binding levels can be correlated to the antibody specificity to CAA fragments. For the most reactive antibodies, the structural changes chosen (β-D-GalpNAc replaced by β-D-GlcpNAc, and β-D-GlcpA replaced by β-D-Glcp6S) completely eradicated the binding. Copyright © by Walter de Gruyter 2005 All Rights Reserved.