Bordetella bronchiseptica fimbrial protein-enhanced immunogenicity of a Mannheimia haemolytica leukotoxin fragment

Leukotoxin produced by Mannheimia ( Pasteurella) haemolytica is an important virulence factor in shipping fever pneumonia in feedlot cattle and is a critical protective antigen. In this study, the immune response to a chimeric protein generated by combining a gene fragment encoding neutralizing epitopes of M. haemolytica leukotoxin and a fimbrial protein gene ( fim N) from Bordetella bronchiseptica was evaluated. The recombinant gene was cloned in a bacterial expression vector under the control of the tac promoter and expressed as a fusion protein with glutathione- S-transferase (GST) in Escherichia coli. Immunization of mice with the recombinant protein, GST-LTXFIM elicited a significantly stronger anti-leukotoxin antibody response than comparable immunizations with GST-LTX fusion proteins lacking FIM N. The GST-LTXFIM was also more stable than GST-LTX during storage at −80 °C, thus alleviating a stability problem inherent to leukotoxin. This chimeric protein may be a candidate for inclusion in new generation vaccines against shipping fever pneumonia.