Liposome potentiation of humoral immune response to lipopolysaccharide and O-polysaccharide antigens of Brucella abortus.

Liposomes were evaluated for their effectiveness as vaccine carriers in the potentiation of the mouse humoral response to the lipopolysaccharide (LPS) and O-polysaccharide (OPS) antigens of Brucella abortus. LPS and OPS were extracted from a pathogenic strain of B. abortus and were encapsulated within multilamellar vesicles. Groups of mice, immunized with liposome-encapsulated and free LPS or OPS, were bled weekly and the specific IgM and IgG levels in the sera were determined by an indirect fluorogenic enzyme-linked immunosorbent assay. Humoral response to these antigens were found to be dose-dependent. Mice immunized with LPS and OPS encapsulated within liposomes were found to have significantly higher IgG levels than mice immunized with free LPS and OPS. In addition, the antibody levels in mice that were immunized with liposome-encapsulated LPS and OPS were more sustained and remained at elevated levels--even after 5 weeks post immunization. As expected, OPS was found to be less immunogenic than LPS, but multiple injections of OPS encapsulated within liposomes greatly improved the immunogenicity. These results indicate that the humoral response to LPS and OPS of B. abortus can be enhanced when these antigens are encapsulated within liposomes.

Immune response of the mouse to gram-negative bacterial outer membrane extracts as assessed with monoclonal antibodies.

Neisseria meningitidis outer membrane extracts of known serotype antigens as well as isolates from a linear carriage study were used to immunize mice for subsequent production of monoclonal antibodies. As well, membrane extracts from one strain of Pseudomonas aeruginosa, serotype M, were used. The degree of specificity of the resulting monoclonal antibodies to the two genera differed markedly when tested with known serotype antigens. That is, antibody from a given clone reacting with more than one serotype specificity was a more frequent occurrence among clones resulting from the Pseudomonas fusion. Preexisting "natural" antibody to several Pseudomonas species is considered at least partially responsible for the diversity of the response to this genus. Evidence is presented for the divergence of specificity with time after immunization with Neisseria.

Type-specific antigens of Neisseria meningitidis serogroup A.

By using Ouchterlony immunodiffusion techniques, we defined three unique antigenic determinants (A1, A2, and A3) among six isolates of Neisseria meningitidis serogroup A. Two of these determinants (A2 and A3) were identified as lipopolysaccharides in nature and were not found to occur on the serogroup B strains of N. meningitidis that we examined. The A1 determinant commonly occurred among the serogroup B strains and was identified as a protein determinant.