An effective vaccine for serogroup B meningococci has yet to be developed and attention has turned to subcapsular antigens of the meningococcus as possible vaccine candidates. Iron binding proteins are being studied, with most interest focused on the transferrin binding proteins (TbpA and TbpB) and the ferric binding protein (FbpA). This study describes the purification of lactoferrin binding protein A (LbpA) from two meningococcal strains and assesses the human isotype-specific serum antibody response to these proteins in patients with proven meningococcal disease due to a range of phenotypes. Overall, fewer than 50% of sera contained IgG that recognised LbpA isolated from either strain and this antibody response was not uniform between the two proteins. There was some evidence that the antibody response varied between meningococcal phenotypes. This study demonstrates that LbpA does not induce a highly cross-reactive antibody response, indicating that it is unlikely to be an effective vaccine antigen.

Subcapsular antigens, including transferrin binding proteins, are being considered as potential vaccines against serogroup B meningococci. This study examined the human isotype antibody responses in cases of meningococcal disease to meningococcal TbpA (transferrin binding protein A) and TbpB (transferrin binding protein B) from two strains (SD and B16B6) expressing high and low molecular mass TbpB respectively. TbpA isolated from both strains were recognised more frequently and higher durable ELISA absorbance values were detected than those detected against TbpB from either strain. These antibody responses to Tbps were independent of the infecting meningococcal strain type. The antibody response to the four proteins was highly variable between individuals and differed significantly against all four antigens. The variability of immune responses to each Tbp from the two strains suggests that a successful vaccine would need to include TbpA and TbpB from a number of strains.