IMMUNOGENICITY EXPRESSED IN PATIENTS WITH BACTEREMIA OF AN EPITOPE SHARED BY ENTEROBACTERIAL AND NEISSERIAL PORIN PROTEINS

A monoclonal antibody (MAb) against an epitope (Po I) on an Escherichi a coli O55 porin protein has shown broad cross-reactivity with other E nterobacteriaceae and with both pathogenic and nonpathogenic Neisseria ceae. In this study, we have measured antibody levels against the Po I site in patients with bacteraemia in order to examine the immunogenic ity of the Po I domain in humans. A MAb-based competition ELISA (cELIS A) was used. Only 20% of healthy controls had detectable levels of ant i-Po I antibodies in serum. Of patients bacteraemic with enterobacteri a (n=45), 11% and 58% showed elevated antibody levels compared to heal thy controls with the first and second serum specimens, respectively, and 73% of these patients showed greater than or equal to 10% increase in the antibody levels. Of patients bacteraemic with N. meningitidis (n=20), only 30% showed greater than or equal to 10% increase in the a ntibody levels when paired serum specimens were tested. Levels of comp eting 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 t hat the highly conserved porin protein domain Po I expressed immunogen icity in humans when present in bacteria which caused bacteraemia. Thi s finding represents a challenge in further investigations on the immu nobiological role of the cross-reacting antibodies.