Abstract
For several reasons the major outer membrane protein from Neisseria gonorrhoeae (gonococcal protein [PI]) is an attractive component for a gonococcal vaccine. This paper describes the influence of two different physical forms of PI on its immunogenic activity. To this end PI was delivered in liposomes and in protein-detergent complexes. In both forms PI was present in a multimeric form. The liposomes were composed of phosphatidylcholine and cholesterol. The effect of dicetylphosphate as a negatively charged amphiphile and three lipoidal adjuvants was investigated. Two lipoidal adjuvants (Avridine and dimethyldioctadecylammoniumbromide) were positively charged amphiphiles, whereas the third one (tridecyl N-acetylmuramyl-L-alanyl-D-isoglutaminate) was neutral. The protein-detergent complexes were also tested in the presence of the lipoidal adjuvants and in an AlPO4-adsorbed form. The liposome preparations were characterized for their size, charge, and residual amount of detergent. The immunogenic activity of PI in all forms was tested in mice. The results of the antibody assays showed that PI in the liposomes was more immunogenic than PI in the complexes. A second dose with liposomes induced only a small booster effect, whereas such a dose with the complexes produced pronounced booster effects. The incorporation of the positively charged lipoidal adjuvants in the liposomes resulted in enhanced booster effects. The highest immunogenic activity of PI after two injections, however, was observed in the complexed form adsorbed to AlPO4.