Immunogenicity expressed in patients with bacteraemia of an epitope shared by enterobacterial and neisserial porin proteins.

A monoclonal antibody (MAb) against an epitope (Po I) on an Escherichia coli O55 porin protein has shown broad cross-reactivity with other Enterobacteriaceae and with both pathogenic and non-pathogenic Neisseriaceae. In this study, we have measured antibody levels against the Po I site in patients with bacteraemia in order to examine the immunogenicity of the Po I domain in humans. A MAb-based competition ELISA (cELISA) was used. Only 20% of healthy controls had detectable levels of anti-Po I antibodies in serum. Of patients bacteraemic with enterobacteria (n = 45), 11% and 58% showed elevated antibody levels compared to healthy controls with the first and second serum specimens, respectively, and 73% of these patients showed > or = 10% increase in the antibody levels. Of patients bacteraemic with N. meningitidis (n = 20), only 30% showed > or = 10% increase in the antibody levels when paired serum specimens were tested. Levels of competing antibodies were similar in the cELISA with N. meningitidis (B: 15: P1, 7, 16) OM coat or E. coli O55 OM coat. The results demonstrated that the highly conserved porin protein domain Po I expressed immunogenicity in humans when present in bacteria which caused bacteraemia. This finding represents a challenge in further investigations on the immunobiological role of the cross-reacting antibodies.