Human immune response to iron-repressible outer membrane proteins of Neisseria meningitidis.

Neisseria meningitidis grown under iron-limiting conditions in vitro expresses additional iron-repressible outer membrane proteins (FeRPs). To see which FeRPs were expressed and immunogenic in human infection, we examined purified membranes from four meningococcal disease isolates with Western blotting of patient sera. Convalescent serum from each patient contained immunoglobulin G (IgG) and IgM antibodies against the homologous 70-kilodalton (kDa) FeRP and IgG antibody to the homologous 94-kDa FeRPs. Three other immunoreactive FeRPs were identified in two or more strains. Neither acute-phase sera nor pooled normal human sera contained appreciable levels of these antibodies. Antigenic cross-reactivity among FeRPs was suggested by the observation that the convalescent sera of two patients contained IgG antibodies reactive with the 70- and 94-kDa FeRPs and IgM antibodies reactive with the 70-kDa FeRPs from all four strains. Additionally, rabbit antiserum against the 70-kDa FeRP from one of these disease isolates contained IgG and IgM antibodies that reacted in Western blots with the 70-kDa FeRPs in all four strains. These results demonstrate that meningococcal FeRPs are expressed and immunogenic in vivo and that certain of these proteins are immunologically cross-reactive.