The class 1 outer membrane protein of Neisseria meningitidis produced in Bacillus subtilis can give rise to protective immunity.

The class 1 outer membrane protein of Neisseria meningitidis B:15:P1.7,16 was expressed in Bacillus subtilis in high yield as intracellular aggregates. These were easy to isolate and the protein (called BacP1) could be solubilized under denaturing conditions. Sera of mice immunized with thus-solubilized BacP1 contained high titres of antibodies that reacted with the class 1 protein of the meningococcal envelope in immunoblots but did not react with native meningococcal envelope in enzyme immunoassays (EIA) or with intact meningococci in bactericidal assays. However, when the BacP1 protein was complexed with heterologous (Salmonella) lipopolysaccharide, the ensuing sera reacted with meningococcal envelope preparations in both EIA and immunoblots, showed subtype-specific bactericidal activity, and were protective in an infant rat meningitis model.