Characterization of a 39 kDa capsular protein of avian Pasteurella multocida using monoclonal antibodies

Abstract The role of a 39 kDa protein of avian Pasteurella multocida in pathogenesis of fowl cholera was investigated using monoclonal antibodies (Mabs). Mabs were prepared by immunization of BALB/c mice with a crude capsular extract (CCE) of P. multocida strain P-1059 (serovar A:3). Totally eight hybridomas producing Mab were obtained. Immunoblot analysis of the hybridomas revealed that all the Mabs recognized a 39 kDa protein of CCE. Treatment of CCE antigen with proteinase K or periodic acid indicated that the epitope recognized was proteinaceous. The Mabs reacted with a major 39 kDa protein of CCE from encapsulated strains but not with any protein of non-capsulated strains indicating that a direct correlation between encapsulation and the 39 kDa protein. Immunoelectron microscopy on strain P-1059 and the non-capsulated derivative P-1059B (serovar -:3) reacting with the Mabs and gold-labeled anti-mouse IgG indicated that the protein is associated with the capsule. The Mabs significantly inhibited the adherence of encapsulated P. multocida strains to chicken embryo fibroblast cells, but only slightly that of non-capsulated strains. Mice passively immunized with the Mabs were protected from lethal challenge with virulent strains P-1059 and X-73 (serovar A:1). Thus the capsular 39 kDa protein was determined to be an adherence factor and a cross-protective antigen of avian P. multocida type A strains.