Outer-membrane protein- and rough lipopolysaccharide-specific monoclonal antibodies protect mice against Brucella ovis

Laboratoire de Pathologie Infectieuse et Immunologie, Institut National de la Recherche Agronomique, Centre de Recherches de Tours, 37380 Nouzilly, France Correspondence should be sent to Dr G. Dubray. Received April 7, 1995 Accepted April 25, 1995 Brucella ovis , a naturally virulent rough Brucella species, is the aetiological agent of ram epididymitis. The identification of protective antigens is necessary to obtain a safe, specific subcellular vaccine. Monoclonal antibodies (MAbs) directed at both brucella outer-membrane proteins (OMPs) and rough lipopolysaccharide (R-LPS) in a mouse protection test were used to identify potential targets for humoral immunity. Mixtures of MAbs directed at the 16·5-, 25–27-, 31-34- and 36-38-kDa OMPs conferred significant protection 7 days after challenge with reference strain B. ovis 63/290 compared with controls receiving either saline or an anti-brucella O-polysaccharide MAb. Furthermore, an anti-R-LPS MAb tested alone conferred protection at a level comparable with that obtained with the mixture of anti-OMP MAbs. The combination of protective OMP MAbs with the anti-R-LPS MAb was also strongly protective. One combination of OMP MAbs, which bound intensely to B. ovis in vitro , was ineffective. These results indicate that B. ovis OMPs and R-LPS are targets for protective antibodies and that they can be regarded as candidates for ram epididymitis subcellular vaccines. * Present address: Laboratorio de Inmunoquimica y Biotecnologia, Facultad de Ciencias Veterinarias, UNICEN, Pinto 339 (7000) Tandil, Argentina.