Immunogenicity and protective efficacy of pertussis toxin subunit S1 produced by Bacillus subtilis

Pertussis toxin (PT) subunit S1 was produced in Bacillus subtilis as a secretory protein designated BacS1. BacS1 was partially purified and used to immunize mice. The sera were tested for PT-neutralizing antibodies and for protective capacity in a mouse model. Unlike previous findings with recombinant S1 from Escherichia coli, the recombinant BacS1 protein induced antibodies that were both neutralizing and protective. An adjuvant was necessary for efficient immunization with BacS1 but not with PT. Of the four adjuvants tested, aluminium phosphate gel was insufficient whereas Freund's incomplete adjuvant, Klebsiella lipopolysaccharide and Ribi's monophosphoryl lipid A-trehalose dimycolate emulsion all resulted in protective antibody production in NIH mice.