Expression, purification and immunologic analysis of three Pasteurella haemolytica A1 28-30 kDa lipoproteins

Three genes, tandemly arranged on the Pasteurella haemolytica A1 chromosome and encoding similar 28-30 kDa proteins, were previously cloned and sequenced by our laboratory. In this study, we demonstrate that the cloned genes encode lipoproteins, as previously suggested by DNA sequence analysis. To further analyze the bovine immune response to these proteins, the individual genes were cloned separately into an expression vector and recombinant forms of the three proteins were purified after expression in Escherichia coli. Sera from cattle vaccinated with live P. haemolytica or P. haemolytica bacterins and from cattle naturally exposed to P. haemolytica recognized each of the recombinant proteins. Vaccination with live or killed whole bacteria did not elicit an immune response of the same quality as that which developed in response to natural infection. A statistically significant correlation existed between resistance to challenge and a high antibody response to one of these three proteins.