IMMUNE-RESPONSE TO INFECTION - EVALUATION OF IMMUNOGENICITY AND PROTECTIVE ACTIVITY IN BALB C MICE OF THE 25-KDA MAJOR OUTER-MEMBRANE PROTEIN OF BRUCELLA-MELITENSIS (OMP25) EXPRESSED IN ESCHERICHIA-COLI/

The antibody response specific to the 25-kDa major outer-membrane prot ein (Omp25) of Brucella melitensis expressed in Escherichia coli was a ssessed in BALB/c mice. Groups of mice were immunised and boosted eith er with sonicated E. coli carrying plasmid pAC2533 - E. coli (pAC2533) - expressing the gene coding for Omp25 (omp25 gene) of B. melitensis, or with E. coli carrying plasmid pUC19 - E. coli (pUC19). One control group received saline. The evolution of antibody responses was invest igated by indirect ELISA with whole rough (R) B. melitensis H38 cells as antigen. Serum antibody titres of mice immunised with E. coli (pAC2 533) were appreciably higher than those of mice immunised with E. coli (pUC19). The specificity to Omp25 of murine antibodies induced by E. coli (pAC2533) was demonstrated by SDS-PAGE and immunoblotting of five B. melitensis strains. Binding of antibody in E. coli (pAC2533) immun e sera to the surface of B. melitensis strains differing in their smoo th lipopolysaccharide (S-LPS) expression was also studied by whole-cel l ELISA and by flow cytometry. Antibody reactivity to R and smooth-rou gh (S-R) was much stronger than that to smooth (S) B. melitensis strai ns, indicating a much better accessibility of Omp25 to antibody on str ains lacking or expressing less O-polysaccharide on their surface. The antibodies to Omp25 were predominantly of IgG2a isotype. The capacity of E. coli (pAC2533) to induce protective immune responses against fo ur challenge strains of B. melitensis was further evaluated in mice. S ignificant reductions in splenic infections, in comparison with mice i mmunised with E. coli (pUC19) and unimmunised (saline injection) mice, were observed in R B. melitensis B115, S-R B. melitensis EP and S B. melitensis H38 infected mice. Protection against S B. melitensis 16M w as not significant. The data from the present study, together with pre vious results, suggest that humoral immunity against probably conforma tional, well-exposed epitopes of the Omp25 could contribute to protect ive mechanisms against B. melitensis infection in mice.