Inhibition of antibody binding to homologous Escherichia coli lipopolysaccharides with purified O antigen polysaccharides in sera from patients with acute pyelonephritis

Abstract

Antibody titers to eight different Escherichia coli O serotype lipopolysaccharide antigens were studied, in the sera from nine patients with acute pyelonephritis, where a bacteriological culture from the urine showed significant growth of E. coli. They were analysed by ELISA. In 8 9 sera, a significant increase in antibody titer to the infecting O serotype was noted. Eight of these sera also showed an antibody response to one or more of the heterologous antigens. In sera from the remaining patient, antibodies only to heterologous antigens were observed. In eight sera, the antibody bound to LPS, homologous with the infecting O serotype and was inhibited by the purified homologous O polysaccharide. One serum was tested for inhibition by a polysaccharide heterologous to the infecting E. coli O serotype. No inhibition was observed with antibodies directed towards the infecting O antigen, but a significant decrease in antibody binding was found with antibodies homologous to the inhibiting O polysaccharide. The observed ‘cross-reactivity’ in the patient's sera may be due to several reasons. Most of our studied patients had experienced repeated low and high urinary tract infections and a majority also had renal scarring. Acute pyelonephritis may induce a polyclonal B-cell activation, which may trigger an anamnestic response of antibodies against other E. coli O serotypes. Furthermore, the patient might be infected with more than one E. coli strain of different O serotypes. It is also possible that common antigenic epitope(s) exist within the core and the O antigen polysaccharide.