Identification of protective outer membrane antigens of Brucella ovis by passive immunization of mice with monoclonal antibodies

Outer membrane proteins (OMPs) and rough lipopolysaccharide (R-LPS), the ma in surface antigens of Brucella ovis, display surface-exposed epitopes. Mix tures of monoclonal antibodies (mAbs) to both antigens were previously show n to protect mice against a B. ovis challenge. To further identify the anti gens involved, seven mAbs against Brucella OMPs (Omp10, Omp16, Omp19, Omp25 , Omp31, Omp2b and Omp1) and three to R-LPS were tested for protection eith er individually or in combinations. Significant reduction in spleen infecti on in challenged mice, relative to controls, was used as the protection cri teri. Controls included nonimmunized mice and mice given an irrelevant, ant i-O-polysaccharide (OPS), mAb. For comparison, a group received a mouse ser um containing antibodies to both OMPs and R-LPS; this serum was prepared by immunization with a. ovis hot-saline extract which, as described previousl y, induces protective immunity in mice and rams. Significant protection was observed with both mAbs to OMPs and R-LPS. mAbs to Omp16, Omp19 and Omp31 afforded the highest protection and prevented the development of splenomega ly. The protective effect of mAb to Omp31 was not interfered with by nonpro tective mAbs in different mixtures. The data presented confirm the protecti ve role of antibodies to OMPs and R-LPS against B. ovis, and identify sever al OMPs, especially Omp31, which are promising candidates for a subunit: va ccine against ram epididymitis. (C) 2000 Editions scientifiques et medicale s Elsevier SAS.