Foal IgG and opsonizing anti-Rhodococcus equi antibodies after immunization of pregnant mares with a protective VapA candidate vaccine.

The research article evaluates if the immune response of pregnant horses, induced by a trial vaccine for the bacterial infection Rhodococcus equi, can be passed on to their foals. It found that the mares vaccinated with a specific protein from R. equi produced stronger immune responses, which were then successfully transferred to their foals.

Study Design and Procedure

• The researchers conducted an experiment on forty-eight pregnant mares (female horses). They divided the mares into three groups: one group was immunized with a protein antigen from R. equi, another group was vaccinated with killed R. equi bacteria, and a control group was not immunized.
• The first protein antigen was derived from a subsect of R. equi called VapA, mixed with a nanoparticle adjuvant (Montanide IMS 3012), which is an agent that enhances the body’s immune response to an antigen. The purpose of using an adjuvant is typically to create a more robust immune response.
• Immunoglobulin G (IgG) levels in the mares’ serum were evaluated, both during their pregnancy and after the birth of their foals. IgG is an antibody that plays a crucial role in the immune system’s response to bacterial and viral infections.
• The strength of opsonic activity, a process that makes the bacteria more susceptible to attack from the body’s immune cells, was also evaluated in this study.
• The incidence of R. equi infections in the newborn foals was recorded for their first six months of life.

Findings

• The mares that were immunized with the VapA protein antigen developed higher IgG levels and stronger opsonic activity than either the control group or the group immunized with the whole killed R. equi.
• These increased IgG levels and opsonic activities were successfully transferred to the foals born to those mares.
• It was observed that none of the foals born to the vaccinated mares developed pneumonia, in contrast to four foals in the control group (non-immunized mares).

Conclusions

• The study suggests that immunizing pregnant mares with the VapA protein antigen associated with a nanoparticle adjuvant could serve as a potent vaccine against R. equi. This passive immunization can potentially protect foals from getting R. equi infection, thus reducing the incidence of pneumonia in young foals.

It is crucial to note that further studies and trials are needed to confirm the effectiveness and safety of this candidate vaccine.