Antibodies against Citrobacter braakii O37 cells recognize the N-glycan of the band 3 glycoprotein of human erythrocyte membrane

The phenomenon of molecular mimicry was found previously for Citrobacter braakii O37, which shared epitopes with human and horse erythrocytes. The aim of this study was to elucidate the basis of the serological cross-reactivity between anti-C. braakii O37 serum and human erythrocytes. The experiments involved analyzing the epitope on the human erythrocyte membrane, that could be recognized by affinity-purified antibodies. The results indicated a specific glycoprotein fraction in immunoblotting, namely band 3, which interacted with the antibodies purified on lipopolysaccharide from C. braakii O37 LPS (LPS O37) and its core affinity columns. Treating the erythrocytes with trypsin, which cleaves glycophorin A, improved the agglutination because band 3 became more available for antibody binding. Isolated band 3 immobilized on an affinity plate could be used to purify antibodies from the anti-C. braakii O37 serum. These antibodies showed a specific reactivity to LPS O37, but not to the related lipopolysaccharide from Salmonella Toucra O48. Furthermore, the inhibition of agglutination with lactose, the diminished interaction of the specific antibodies purified on LPS O37 with endo-beta-galactosidase-treated band 3, and the reactivity of these antibodies to the 40-kDa fragment of band 3 but not to its trypsin-elaborated 60-kDa fragment, all indicated that the epitope is located on the N-glycan of band 3.