Serum antibody responses in horses and mice following immunization with Actinobacillus equuli outer membrane proteins and recombinant Aqx toxin.

The study examines the immune responses in horses and mice after they’ve been vaccinated with outer membrane proteins (OMPs) and/or recombinant A. equuli toxin (rAqx) of an bacteria named Actinobacillus equuli. This is done to see how potent these substances are in provoking an immune response.

Research Design and Process

• The researchers used two groups of subjects: a group of mice that had not been previously exposed to the bacteria and a group of mares, which had been naturally exposed.
• For the mice, vaccinations were administered under the skin on the first and 21st days with three different doses of A. equuli OMPs, rAqx, or both. The doses used were 5, 25 or 50μg. In addition to the vaccination, the mice were also given Freund’s incomplete adjuvant (FIA), which is used to boost the immune response.
• For the mares, vaccinations were administrated subcutaneously on the first and 21st days with 100μg OMPs, 100μg rAqx, or a combination of 50μg of each antigen, along with FIA.
• After the vaccinations, the researchers monitored the levels of antibodies in the subjects against whole bacterial cells (WBCs), OMPs, and Aqx. For mice, they did so on the 21st and 42nd days, while for mares, they did the monitoring at seven-day intervals for the first 42 days, then on the 56th, 70th, 154th, and 238th days.

Findings of the Study

• The vaccination stimulated an apparent dose response in mice to OMPs and Aqx, suggesting that the higher the dose, the stronger the immune response.
• In mares that had naturally acquired pre-existing antibodies, vaccination enhanced antibodies against OMPs and Aqx. This indicates that previous exposure to the bacteria might increase the effectiveness of the vaccination.
• No evidence of interference was observed with the antibody responses when OMPs and rAqx were combined before vaccination. This suggests that these substances could potentially be combined in a single vaccine without compromising the performance.