Antigenic relationships among the porin proteins of encapsulated Haemophilus influenzae clones

Monoclonal antibodies (MAbs) specific for Haemophilus influenzae were generated to identify antigenic determinants shared among encapsulated H. influenzae clones. Sixteen MAbs reacted by Western immunoblot with a protein of an approximate molecular size of 40 kilodaltons corresponding to the P2 major outer membrane protein (porin). These MAbs also reacted with purified and recombinant H. influenzae porin. Fourteen of the MAbs recognized cell surface-exposed epitopes, and two of the MAbs, P2-16 and P2-17, identified epitopes that are not present or are not accessible on the cell surface. The reactivity spectrum of the MAb panel was studied by dot immunoassay against 32 serologically nontypeable and 119 encapsulated H. influenzae strains recovered worldwide, representing the major serotype, a, b, and d clone families. MAbs P2-4 and P2-6 recognized only serotype b clones assigned to primary phylogenetic division I. These clones account for more than 99% of all invasive episodes worldwide. MAbs P2-3, P2-8, and P2-11 reacted with division I serotype b isolates and also identified all genetically allied strains expressing serotype a and d polysaccharide capsules. In contrast, none of the 16 MAbs reacted with genetically divergent serotype a or b clones assigned to primary phylogenetic division II. These results demonstrate that, in general, the patterns of P2 protein surface epitope exposure are cognate with genetic lineages of encapsulated H. influenzae strains and support the hypothesis that the population structure of encapsulated H. influenzae is predominantly clonal.