Characterization of an enterobacterial common antigen (ECA) epitope recognized by anti-ECA-tetanus toxoid conjugate serum.

The antigenic reactivity of both native and chemically modified enterobacterial common antigen (ECA) with anti-ECA-tetanus toxoid (TT) conjugate serum was investigated. The results obtained suggest that reduction of the carboxyl group of the mannosaminuronic acid component of ECA diminishes, but does not destroy its antigenic reactivity. Each of the sugar components were found to contribute to its reactivity with anti-ECA-TT conjugate serum, indicating that the trisaccharide repeating unit represents the ECA epitope. A nonasaccharide (trimer of the ECA repeating unit) inhibited antibody binding better than the hexasaccharide dimer, a finding which suggests that oligosaccharide conformation also makes a contribution to its inhibitory activity.