Intranasal immunization with immunogenic epitopes of pasteurella hemolytica and cholera toxin subunit B

Pasteurella hemolyticaM/i> A1 is the predominant bacterium implicated in pneumonic pasteurellosis, or shipping fever disease, of cattle. P. hemolytica A1 produces many virulence factors, but the one researched the most is a potent, cytotoxic exotoxin referred to as leukotoxin. This leukotoxin is specific for ruminant leukocytes and is a major contributor to the lesion formation observed in the lungs of calves with shipping fever.Attempts at vaccinating against this bacterium have indicated that the leukotoxin must be included in the vaccine preparations for it to be effective in protecting against shipping fever. In previous work a murine hybridoma producing a monoclonal antibody capable of neutralizing the leukotoxin was cloned. Studies with this monoclonal antibody indicated that it recognized an epitope in the carboxyl one-third of the toxin. This epitope was,located by fragmentation of the carboxyl domain. These fragments were used to locate the epitope between amino acids 868-939. These leukotoxin fragments were also tested for possible immunogenicity. One of these fragments, JM-2, contained the protective epitope and was capable of eliciting high titers of serum leukotoxin neutralizing antibodies when administered intraperitoneally in mice and subcutaneously in rabbits.The present study was undertaken to determine if the epitopes of JM-2 responsible for the neutralizing response were functional if introduced mucosally by intranasal immunization. The results of this study indicate that JM-2 alone is not effective in eliciting an immune response, but JM-2 administered in conjunction with cholera toxin subunit B is effective in eliciting a response. Intranasal immunization with JM-2 and cholera toxin subunit B elicited a leukotoxin-specific mucosal antibody response and a serum neutralizing response. The serum neutralizing response observed following intranasal immunization was greater than that observed following intraperitoneal immunization. Since shipping fever is a disease that affects the respiratory tract, a mucosal vaccine against this disease would be ideal. This study determined the potential of JM-2 as a component of a mucosal vaccine against P. hemolytica A1.