Modulation of immune responses in Balb/c mice vaccinated with Brucella abortus Cu-Zn superoxide dismutase synthetic peptide vaccine.

Three peptides, peptide 1 (GGDNYSDKPEPLGG), peptide 2 (LAEIKQRSLMVHGG) and peptide 3 (GGAPGEKDGKIVPAG), were synthesized based on the amino acid sequence of Brucella abortus Cu-Zn superoxide dismutase. These peptides were selected on the basis of their predicted hydrophilicity, flexibility and antigenicity profiles. The three peptides, singly or in combination, with or without the adjuvant monophosphoryl lipid A were administered to Balb/c mice as vaccines for brucellosis. The protective and immune responses induced by the peptide vaccines after challenge exposure to virulent B. abortus strain 2308 were compared to those obtained with salt-extractable proteins (BCSP) vaccine prepared from B. abortus strain 19, recombinant B. abortus Cu-Zn superoxide dismutase (rSOD) vaccine and non-vaccinated mice. Mice vaccinated with 30 micrograms of peptide 3 plus 50 micrograms monophosphoryl lipid A afforded two logs of protection (reduction in log10 colony-forming units compared with control mice) and one log of protection when given without monophosphoryl lipid A, whereas 5 micrograms of the salt-extractable proteins afforded three logs of protection. The rSOD and peptides 1 and 2 given with or without monophosphoryl lipid A afforded no protection. Superoxide dismutase-specific IgG antibody was present in postchallenge sera only if BCSP was present in the vaccine. Peptide-specific IgG antibodies were present in postchallenge sera of mice, and antibody concentrations were generally enhanced when monophosphoryl lipid A was included in the vaccine. The overall results with the peptide vaccines suggest that peptide 3 probably contains a specific sequence preferentially recognized by the cellular immune system leading to modulation of immune response mechanisms responsible for decreasing splenic infection.