An epitope shared by enterobacterial and neisserial porin proteins.

A murine monoclonal antibody (MAb F9-16) raised against a porin protein epitope called Po I of an E. coli 055 strain showed broad cross-reactivity with bacteria within the Enterobacteriaceae, and also recognized neisseriae and moraxellae. In an immunodot assay, the antibody was bound by 32/33 strains of neisseriae and moraxellae after SDS treatment of the bacteria. Testing intact bacteria, 11/33 isolates showed definite MAb binding, including serogroup A and B meningococci. In Western blotting, the anti-Po I MAb targeted the gonococcal porin proteins PIA and PIB, and class 1, class 2, and class 3 porins of meningococci. The MAb showed no reactivity against decapeptides which corresponded to the whole length of a meningococcal class 1 porin protein of the subtype P1, 7, 16. These findings accord with the inference that enterobacterial, neisserial and moraxellae porin proteins share an epitope (Po I) which is determined by the three-dimensional rather than by the primary structure of the proteins and that this epitope is shielded in most isolates but surface-exposed in some isolates, including some strains of meningococci. Since Po I is broadly distributed among commensal and pathogenic bacteria and has demonstrated immunogenicity in humans, this epitope may play a role in elicitation of "normal" antibodies with immunoprotective activity.