Effects of two commercially available immunostimulants on leukocyte function of foals following ex vivo exposure to Rhodococcus equi.

This study investigates how two commercially available immunostimulants impact the function of certain white blood cells in foals after exposure to the bacterium, Rhodococcus equi.

Study Objective and Design

• The primary goal of this research was to understand the influence of immunostimulants on three types of white blood cells – neutrophils, macrophages, and lymphocytes – after these cells were exposed to Rhodococcus equi ex vivo (outside a living organism).
• The researchers used 18 foals in their study, dividing them randomly into three treatment groups. The treatments involved the use of inactivated Propionibacterium acnes (PA), inactivated parapoxvirus ovis (PPVO), or a saline solution (serving as a control), delivered on specific days of the experiment.
• The research team collected bronchoalveolar lavage (BAL) fluid and blood from the foals at regular intervals over 36 days to measure various cell functions and changes.

Main Findings

• The study found noticeable improvements in neutrophils’ ability to phagocytize (engulf and destroy) Rhodococcus equi and trigger oxidative bursts (a mechanism immune cells use to destroy pathogens) in foals treated with PPVO, compared to the baseline data.
• On the 24th day, the PPVO-treated foals exhibited better neutrophilic phagocytosis and oxidative burst activity than those treated with PA.
• The researchers observed that PA treatment significantly inhibited the proliferation of Rhodococcus equi within monocyte-derived macrophages (a type of white blood cell) on the 12th day compared to the control group.
• The capacity of Rhodococcus equi to multiply within BAL macrophages lessened notably over time, with older foals showing lower replication rates than younger ones, disregarding the treatment type.
• Also, on the 12th day, the foals treated with PPVO showed significantly higher induction of two types of immune-system-activating proteins (TNF-α and IL-12 p40) in monocyte-derived macrophages and BAL macrophages infected with Rhodococcus equi compared to the control group.
• The study found no marked difference among the groups in terms of lymphoproliferative responses (the ability of lymphocytes to multiply) and IFN-γ induction (an important protein for immune responses).

Overall Interpretation

• The results imply that while the use of commercially available immunostimulants can have differential effects on the immune responses of foals, one stimulant (PPVO) seemed to enhance certain key aspects more effectively than the other (PA).
• Future studies will help unfold any potential clinical applications or implication of these findings, particularly in the context of therapies for Rhodococcus equi infections in horses.