Serum antibody responses of cattle vaccinated with partially purified native Pasteurella haemolytica leukotoxin

The objective of these experiments was to study the serum antibody responses of cattle to partially purifed, native Pasteurella haemolytica A1 leukotoxin (LKT) formulated with a commercial aluminum hydroxide-DDA-bromide adjuvant. In two experiments, calves received two intramuscular injections 21 day's apart and sera were obtained periodically. Serum antibody responses to P. haemolytica outer membrane proteins (OMPs), formalinized P. haemolytica, and LKT were determined. In Experiment A, Holstein calves (140 kg each) were vaccinated with either 10, 1.0 or, 0.1 mu g of LKT, 10(9) c.f.u. of live P. haemolytica, or adjuvanted diluent. In Experiment B, mixed-breed beef calves (200 kg each) were vaccinated with either 100, 50 or 10 mu g of LKT, 10(9) c.f.u. live P. haemolytica, or adjuvanted diluent. Vaccination of dairy calves with 10 mu g of partially purified LKT stimulated LKT neutralizing antibody responses similar to those stimulated by vaccination of one calf with live P. haemolytica. In Experiment B, which used larger and different breeds of cattle, two vaccinations 3 weeks apart with 50 mu g LKT stimulated LKT neutralizing responses equivalent to ol gr eater than those stimulated by vaccination with live P. haemolytica. In both experiments, LKT vaccines stimulated only low antibody responses to formalinized P. haemolytica ol to OMPs. (C) 1997 Elsevier Science Ltd.