Immunity of cattle following vaccination with a Mannheimia haemolytica chimeric PlpE-LKT (SAC89) protein.

UNLABELLED: We developed several chimeric PlpE-leukotoxin (LKT) constructs containing the major epitope of Mannheimia haemolytica outer membrane lipoprotein PlpE (epitope R2) and the neutralizing epitope of M. haemolytica LKT (NLKT) [Ayalew et al. Mannheimia haemolytica chimeric protein vaccine composed of the major surface-exposed epitope of outer membrane lipoprotein PlpE and the neutralizing epitope of leukotoxin. Vaccine 2008;26(38):4955-61]. Vaccination of mice with these PlpE-LKT chimeric proteins stimulated anti-PlpE antibodies that caused complement-mediated bacteriolysis of M. haemolytica as well as neutralizing anti-LKT antibodies. Chimeric protein SAC89, which contains two copies of R2 and two copies of NLKT, generally stimulated the best overall responses in mice. The objectives of the current study were: (1) to determine through a dose titration study if vaccination of cattle with SAC89 stimulated antibodies to both PlpE and LKT and (2) evaluate SAC89-induced immunity against experimental M. haemolytica challenge of cattle. In the dose titration study, vaccine doses ranged from 100 to 400 microg. SAC89 significant anti-M. haemolytica surface and LKT antibodies were detected following vaccination with each dose. The vaccination/challenge study was conducted with 30 weaned beef cattle distributed among four groups: Control (no vaccine), 100 microg SAC89, M. haemolytica Bacterin, and SAC89+M. haemolytica bacterin. On day 42 after two vaccinations, cattle were challenged transthoracically with M. haemolytica. There was significant reduction (p<0.05) in lesion scores for the SAC89+bacterin-vaccinated group (74.6% reduction compared to control lesion scores) when compared to the other groups (34.7% and 35.6% reduction compared to control lesion scores). Evaluation of antibody responses demonstrated that the control group failed to develop antibody responses to M. haemolytica surface antigens or to LKT. Bacterin-vaccinated cattle developed anti-M. haemolytica antibodies after the second vaccination. SAC89- and SAC89+bacterin-vaccinated groups developed significant antibody responses 14 days after the first vaccination and further significant increases in antibodies after the second vaccination. CONCLUSIONS: Vaccination with the chimeric protein SAC89 in conjunction with a M. haemolytica bacterin stimulated significant protection against a severe transthoracic challenge with the bacterium.

Serum antibodies in mares and foals to Actinobacillus equuli whole cells, outer membrane proteins, and Aqx toxin.

Actinobacillus equuli is carried in the alimentary tract of mares and can cause severe septicemia of neonatal foals. A hemolytic subspecies, A. equuli subsp. haemolyticus, and a non-hemolytic subspecies, A. equuli subsp. equuli, have been identified. Hemolytic strains produce the RTX toxin Aqx. The purpose of this study was to demonstrate sequentially in two sets of mare-foal pairs antibodies to A. equuli whole bacterial cells, outer membrane proteins, and recombinant Aqx and to compare the transfer of antibodies to these antigens between mares and their foals. Two mare/foal sets of sera were evaluated. Cohort A consisted of 18 mare-foal pairs obtained in the spring of 2005. Cohort B consisted of 10 mare-foal pairs obtained in the spring of 2006. For both sets, mare and foal sera were obtained immediately after foaling and prior to nursing (time 0) as well as at 12 and 24h and daily thereafter for 7 days. For Cohort B, sera were also obtained 30 days after birth. At parturition all mares had detectable antibodies to A. equuli whole cells and outer membranes; however, of those mares, two in Cohort A had undetectable antibodies to Aqx and their foals likewise had undetectable anti-Aqx antibodies. Antibodies against whole cells, outer membrane proteins, and Aqx were readily transferred from mares to foals. In most cases, there were significant correlations (p<0.05) between antibodies against whole cells, outer membrane proteins, and Aqx in mares' sera at the time of parturition and foal sera 24 after birth. Antibodies against the three antigen preparations had declined insignificantly (p>0.05) by day 30.