Analysis of Brucella Lipopolysaccharide with Specific and Cross-reacting Monoclonal Antibodies

Monoclonal antibodies which bind Brucella A lipopolysaccharide (LPS)-specific, M LPS-specific, or cross-reactive epitopes were used as reagents in quantitative dot blot, Western blot (immunoblot), and immunoprecipitation analysis of Brucella whole cells, whole-cell extracts, and purified LPS preparations. This set of monoclonal antibodies detected four unique epitopes on Brucella LPS. The specificity of monoclonal antibodies reactive with Brucella unique (A and M) and common (C and C/Y) LPS epitopes was demonstrated by blot analysis. The serotype specificity of monoclonal antibodies for A LPS of B. abortus 1119.3 or M LPS of Brucella melitensis 16M was confirmed. Type C monoclonal antibodies recognized epitopes on Brucella A and M LPS and did not cross-react with Yersinia enterocolitica O:9. In Western blots, type C monoclonal antibodies were bound by epitopes on Brucella A and M LPSs ranging in Mrs from 30,000 to 70,000, relative to marker proteins. Type C/Y monoclonal antibodies were cross-reactive with Y. enterocolitica O:9 and recognized Brucella A LPS epitopes with a restricted Mr ranging only from 40,000 to 50,000, relative to marker proteins. Type C/Y monoclonal antibodies also displayed a more restricted pattern of binding to Brucella M LPS. The monoclonal antibodies were able to detect 5 to 50 pg of a purified A LPS preparation in dot blots. The limits of detection by the monoclonal antibodies of a purified M LPS preparation ranged from 0.05 to 50 pg. Monoclonal antibody analysis of whole-cell preparations also demonstrated quantitative differences in the presence of the respective epitopes. The binding profiles of the monoclonal antibodies to Brucella whole cells varied between acetone- and chloroform-killed organisms as well as between species and strains. The lower limit of detection of any whole-cell preparation by the dot blot technique was 10(5) CFU. Binding profiles in Western blots and endotoxin activity of immunoprecipitates obtained with these monoclonal antibodies further defined the Brucella LPS antigens. These monoclonal antibodies and the techniques described may be useful in monitoring the antigenic content of Brucella vaccines and diagnostics.