Biological activity of bacterial cell-wall components: immunogenicity of the bacterial extract OM-89.

The bacterial extract OM-89 is used for the treatment of recurrent infections of the urinary tract. It consists of immunostimulating components derived from 18 Escherichia coli bacterial strains and constitutes a non-specific leukocyte activator. We here could demonstrate for the first time that, in a long-term immunization protocol, OM-89 acts as an effective immunogen in mice. After multiple parenteral applications of the extract, OM-89-specific antisera were obtained; the maximum serum antibody content was found after 6-9 immunizations. The antibodies induced were mainly of the IgG isotype, and a weak increase of IgM was observed. The sera also bound to the bacterial strains used for the preparation of the extract. Moreover, we could show that defined bacterial cell-wall components like protein I (porin), lipopeptide and murein were recognized. Our findings on the immunogenicity of OM-89 might partially explain the therapeutic effect of the extract as shown in clinical studies.