Molecular characterization of the 98-kilodalton iron-regulated outer membrane protein of Neisseria meningitidis.

When grown under iron limitation, Neisseria meningitidis expresses several additional outer membrane proteins (OMPs), which were studied to assess their vaccine potential. Two monoclonal antibodies were obtained against a 98-kDa OMP of strain 2996 (B:2b:P1.2). Cross-reactivity studies revealed that the two antibodies reacted with 44 and 42 of 74 meningococcal strains, respectively. The antibodies did not block the binding of transferrin or lactoferrin to intact cells. The structural gene for the protein, tentatively designated iroA, was isolated and sequenced. Computer analysis revealed homology to the ferric siderophore receptors in the outer membrane of Escherichia coli and to gonococcal transferrin-binding protein 1 (TbpA). The high degree of cross-reactivity and the results of Southern blot analyses, which showed that the iroA gene is also present in strains that did not react with the monoclonal antibodies, suggest that the 98-kDa OMP is well conserved among meningococci and that it is a suitable vaccine candidate. However, the antibodies were not bactericidal in an in vitro assay with human complement.