Human antibody responses to R3-core epitopes on the lipopolysaccharide of Escherichia coli O157

AIMS: To establish the incidence of serum antibodies binding to the R3-core lipopolysaccharide (LPS) of verocytotoxin-producing Escherichia coli (VTEC) O157, in patients with serum antibodies to E. coli O157 LPS, and to characterize the class(es) of antibodies binding to epitopes on the R3-core. METHODS AND RESULTS: SDS-PAGE profiles of LPS prepared from VTEC O157 were used in combination with immunoblotting to detect and characterize serum antibodies binding to the R3-core LPS of VTEC O157. Of 417 sera, referred to the Laboratory of Enteric Pathogens (LEP) for routine O157 serology and found to have serum antibodies to long-chain VTEC O157 LPS, 31 had antibodies binding to the R3-core of VTEC O157 LPS. The majority of the 31 sera contained IgA-class antibodies to both long-chain and R3-core LPS epitopes. Patients who did not develop haemolytic uraemic syndrome (HUS) produced antibodies of the IgM class to R3-core and IgG-class antibodies to long-chain LPS more frequently than patients with HUS. CONCLUSIONS: Only 7.4% of sera received by the LEP, and shown to have antibodies to VTEC O157 LPS, contained antibodies binding to the R3-core of VTEC LPS. Most sera contained IgA-class antibodies to both long-chain and R3-core LPS epitopes. SIGNIFICANCE AND IMPACT OF THE STUDY: Patients infected with VTEC O157 produced antibodies binding to the R3-core epitopes of VTEC O157 LPS only rarely, and these antibodies are unlikely to interfere with the serodiagnosis of infections caused by these organisms.