Characterization of smooth Brucella lipopolysaccharides and polysaccharides by monoclonal antibodies.

Two mouse monoclonal antibodies (mAb) generated to the M antigen of Brucella melitensis 16M were analysed. Binding profiles of both monoclonals were established by a competitive enzyme-linked immunosorbent assay using chemically defined lipopolysaccharides, O polysaccharides and native hapten polysaccharides from B. melitensis 16M, B. abortus 544 and Yersinia enterocolitica O:9. Using this assay, significant differences in the reactivity of both antibodies were found with A and M antigens from Brucella spp. and the O polysaccharide from Y. enterocolitica O:9. These findings are consistent with the simultaneous expression of A and M epitopes on the lipopolysaccharide of all smooth Brucella strains. Quantitatively similar inhibitory powers were established for the native hapten and O polysaccharide from B. melitensis 16M. However, different behaviour was observed between both antigenic preparations obtained from B. abortus 544. The use of lipopolysaccharide-M-specific mAb in different serological tests instead of polyclonal antisera may be of great practical use for minimizing the risk of the appearance of cross-serological reactions between smooth Brucella strains and Y. enterocolitica O:9.