Mucosal and systemic antibody responses to the lipopolysaccharide of Escherichia coli O157 in health and disease

Mucosal immunity in the gastrointestinal (GI) tract is a primary defence ag ainst GI pathogens. We hypothesise that a mucosal response to lipopolysacch aride (LPS), especially to the common (core) determinants of GI pathogenic Escherichia coli strains, is protective. The aims of this study were to inv estigate the specificities, levels and development of humoral responses in health and GI disease to the R3 LPS core and O-polysaccharide of E. coli O1 57. The purpose was to try to predict whether vaccination or passive immuni sation might induce protection. Wherever possible, paired whole gut lavage fluid (WGLF) and serum samples were collected for comparison of the mucosal and systemic responses. Matched saliva samples were also collected from so me study groups. The patient groups included those with acute E. coli O157 disease (serum only), patients convalescing after E. coli O157 infections, and patients undergoing routine investigation for GI conditions but subsequ ently shown to be immunologically normal. Some samples of WGLF from patient s with Crohn's disease (CRO) and ulcerative colitis (UC) were included to a llow comparisons with patients with inflammatory conditions known to alter antibody secretion in the GI tract. The healthy groups from whom serum and saliva only were taken included blood donors, healthy volunteers and a grou p of slaughterhouse workers. This latter group was likely to have been expo sed regularly to faecal bacteria from animals and antibody specificities mi ght have been expected to be different from other healthy individuals. Leve ls and classes of antibodies were determined by ELISA with microtitration p lates coated with polymyxin complexes of whole LPS extracted from E. coli O 157 and LPS from the E, coli R3 rough mutant. Antibodies of IgG and IgM cla sses were measured in serum and IgA was measured in WGLF and saliva. IgG an tibodies to the O157 LPS and the R3 core oligosaccharide were detected in t he serum of healthy blood donors. Patients with acute E. coli O157 disease showed elevated levels of serum IgM to O157 LPS and R3, with IgG levels rai sed only to R3. In serum from convalescent patients, IgG to O157 LPS was si gnificantly above the control groups only in the period 6-16 weeks after in fection. Total IgA levels were similar in WGLF specimens from all groups, e xcept the patients with UC, whose levels were much higher. Specific IgA lev els were higher in the E, coli O157 convalescent group, but there were no s ignificant correlations overall. UC patients had significantly lower levels of IgA to O157 and CRO patients had higher O157 IgA levels than UC patient s and healthy volunteers. In serum, inhibition of ELISA showed that the res ponse to the O157 LPS was due in part to a response to the R3 oligosacchari de component. This response was much more pronounced in the healthy and non -O157 groups than in convalescent patients. There was no correlation betwee n specific IgA antibody levels in saliva and matched specimens of WGLF, and levels in sequential saliva specimens fluctuated widely. The significant I gG and IgA responses to the R3 core suggest that there is immunological mem ory to this oligosaccharide LPS component which may have a role in protecti on against E. coli LPS both systemically and locally in the GI tract. Boost ing of this mucosal response to the LPS core, either naturally through expo sure or by active or passive immunisation, may confer protection. Finally, antibody responses to E. coli O157 must be interpreted with caution, as the response detected is a sum of responses to the O-specific polysaccharide a nd the R3 core.