Identification of immunogenic outer membrane proteins of Pasteurella multocida 3:A in rabbits

Four groups of protective rabbit immune sera were used to identify Pasteurella multocida outer membrane immunogens by a radioimmunoprecipitation procedure and Western blot (immunoblot) analysis. These are rabbit hyperimmune sera against KSCN extract of P. multocida (group 1) and rabbit immune sera against the KSCN extract of P. multocida (group 2), the outer membrane of P. multocida (group 3), and live P. multocida cells (group 4). Rabbits mounted an antibody response to 18 proteins found in the outer membrane of P. multocida, and the major antibody activities were directed to the 27,000-molecular-weight outer membrane protein (27K protein), as well as the 37.5K, 49.5K, 58.7K, and 64.4K outer membrane proteins. These outer membrane immunogens appear to be exposed on the cell surface and accessible to antibodies, since adsorption of these immune sera with intact P. multocida cells resulted in a significant reduction of antibody activities directed against these proteins, especially the 37.5K protein. Antibodies eluted from immune serum-P. multocida cell complexes were reactive to the 37.5K immunogen, confirming that this protein is exposed on cell surface and accessible to antibodies. Western blot analyses with group 1, 3, and 4 immune sera confirmed that the 27K, 37.5K, 49.5K, 58.7K, and 64.4K proteins are the major outer membrane immunogens of P. multocida in rabbits. Lung lavages of immunized rabbits also contained similar antibody activities directed against several outer membrane proteins, with major activities against the 37.5K and 64.4K proteins.