Monoclonal antibodies to Brucella rough lipopolysaccharide: characterization and evaluation of their protective effect against B. abortus.

We characterized 4 monoclonal antibodies (mAb) specific for rough lipopolysaccharide (R-LPS) of Brucella. mAb were selected by enzyme-linked immunosorbent assay (ELISA) on whole B. abortus 45/20 rough cells and R-LPS from B. melitensis B115 rough cells. Specificity was confirmed by immunoblot analysis using R-LPS and smooth LPS (S-LPS) preparations. Anti-R-LPS revealed the low molecular mass R-LPS molecules below 20.1 kDa in the R-LPS and S-LPS preparations as well as the typical A and M patterns in high molecular mass S-LPS molecules (between 21.5 and 66 kDa) in the S-LPS preparations. An O-polysaccharide-specific mAb revealed only high molecular mass S-LPS molecules in the S-LPS preparation. In ELISA the anti-R-LPS mAb bound better on rough than on smooth B. abortus 544 whole cells, and this was confirmed by immunoelectron microscopy. Protective activity of anti-R-LPS mAb of different isotypes was tested on mice and compared with an S-LPS-specific mAb. Only the IgG3 mAb reduced significantly the splenic infection but did not reach the level of protection conferred by the S-LPS-specific mAb.