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 cr itical protective antigen, In this study, the immune response to a chimeric protein generated by combining a gene fragment encoding neutralizing epito pes of M. haemolytica leukotoxin and a fimbrial protein gene (fim N) from B ordetella bronchiseptica was evaluated. The recombinant gene was cloned in a bacterial expression vector under the control of the tac promoter and exp ressed as a fusion protein with glutathione-S-transferase (GST) in Escheric hia coli. Immunization of mice with the recombinant protein, GST-LTXFIM eli cited a significantly stronger anti-leukotoxin antibody response than compa rable immunizations with GST-LTX fusion proteins lacking FIM N. The GST-LTX FIM was also more stable than GST-LTX during storage at - 80 degreesC, thus alleviating a stability problem inherent to leukotoxin. This chimeric prot ein may be a candidate for inclusion in new generation vaccines against shi pping fever pneumonia. (C) 2001 Elsevier Science Ltd. All rights reserved.