Expression of Neisseria meningitidis iron-regulated outer membrane proteins, including a 70-kilodalton transferrin receptor, and their potential for use as vaccines

Abstract

The iron-regulated proteins (IRPs) of five group B meningococcal strains expressing class 2 outer membrane proteins were compared with those of five strains expressing class 3 proteins. Three to four high-molecular-weight IRPs were expressed by each strain, but their molecular sizes varied between strains and were not related to class 2 or 3 protein expression. Transferrin and hemoglobin could be used as a sole iron source. By using anti-human transferrin antibodies, it was shown that meningococcal cells and purified outer membranes bound transferrin. Growth under conditions of iron limitation caused a several-fold increase in the amount of transferrin bound to the cell surface. The transferrin-binding protein was detergent solubilized from outer membranes and partially purified. The isolated protein bound human transferrin and had an apparent molecular mass of 70 kilodaltons. To evaluate the potential of vaccines containing IRPs, we prepared outer membrane vaccines from strains M986-NCV-1 (M986) (--:2a: P1.2) and 44/76-M25 (44/76) (--:15:P1.15) grown to fully express their IRPs. Both vaccines induced significant anti-IRP antibodies as measured by enzyme immunoassay and by Western immunoblot with both M986 and 44/76 outer membranes. By Western blot analysis, the M986 vaccine induced antibodies to two different IRPs, one of which was shared with 44/76. Since the IRPs are major in vivo-expressed outer membrane proteins and are required for survival in vivo, these proteins should be evaluated for their usefulness in a group B meningococcal vaccine.