Recombinant Mannheimia haemolytica serotype 1 outer membrane protein PlpE enhances commercial M. haemolytica vaccine-induced resistance against serotype 6 challenge

Mannheimia haemolytica outer membrane protein PlpE, a major immunogenic outer membrane lipoprotein has identical sequences in serotypes 1 (S1) and S6. Recombinant outer membrane lipoprotein PlpE (rPLpE) from M. haemolytica S1 was added to commercial M. haemolytica S1 vaccines to determine if it would enhance vaccine-induced immunity against heterotypic M. haemolytica S6 challenge. Serum antibody responses to M. haemolytica whole cells, leukotoxin and rPlpE were measured. Experiment 1 consisted of four vaccine groups: controls, 100 μg rPlpE, M. haemolytica Bacterin-Toxoid (One Shot™) and M. haemolytica Bacterin-Toxoid + 100 μg rPlpE. Vaccines were given on day 0. On day 21, calves were challenged transthoracically with M. haemolytica S6. Lung lesion scores and percentage lesion reduction were 6.3 ± 2.0 for controls, 3.6 ± 2.4 for rPlpE vaccinates (42.9% reduction), 3.4 ± 1.5 for One Shot-vaccinates (46.0% reduction), and 2.4 ± 1.4 for One Shot/rPlpE vaccinates (61.9% reduction). Experiment 2 consisted of four vaccine groups: controls, 100 μg rPlpE, M. haemolytica toxoid (Presponse®), and M. haemolytica toxoid + 100 μg rPlpE. On day 28, calves were challenged transthoracically with M. haemolytica S6. Lung lesion scores and percentage lesion reduction were 8.1 ± 2.2 for controls, 4.4 ± 4.7 for the rPlpE vaccinates (45.7% reduction), 4.8 ± 2.2 for Presponse-vaccinates (40.7% reduction), and 2.0 ± 1.2 for Presponse/rPlpE vaccinates (75.3% reduction). These results indicate that addition of rPlpE from M. haemolytica S1 can enhance commercial M. haemolytica vaccine-induced resistance against experimental challenge with M. haemolytica S6.