AN EPITOPE SHARED BY ENTEROBACTERIAL AND NEISSERIAL PORIN PROTEINS

A murine monoclonal antibody (MAb F9-16) raised against a porin protei n epitope called Po I of an E. coli O55 strain showed broad cross-reac tivity with bacteria within the Enterobacteriaceae, and also recognize d neisseriae and moraxellae. In an immunodot assay, the antibody was b ound by 32/33 strains of neisseriae and moraxellae after SDS treatment of the bacteria. Testing intact bacteria, 11/33 isolates showed defin ite MAb binding, including serogroup A and B meningococci. In Western blotting, the anti-Po I MAb targeted the gonococcal porin proteins PIA and PIE, and class 1, class 2, and class 3 porins of meningococci. Th e MAb showed no reactivity against decapeptides which corresponded to the whole length of a meningococcal class 1 porin protein of the subty pe P1, 7, 16. These findings accord with the inference that enterobact erial, neisserial and moraxellae porin proteins share an epitope (Po I ) which is determined by the three-dimensional rather than by the prim ary structure of the proteins and that this epitope is shielded in mos t isolates but surface-exposed in some isolates, including some strain s of meningococci. Since Po I is broadly distributed among commensal a nd pathogenic bacteria and has demonstrated immunogenicity in humans, this epitope may play a role in elicitation of ''normal'' antibodies w ith immunoprotective activity.