Effect of Rhodococcus equi on equine polymorphonuclear leukocyte function.

This study investigates the effects of Rhodococcus equi, a bacterium that often infects horses, on the function of horse polymorphonuclear leukocytes (PMNs), a type of white blood cell. The research reveals that R. equi can suppress certain mechanisms of PMN function, suggesting that the bacterium uses these methods to survive inside of the host cells.

Process and Methodology

• The researchers first developed a procedure to isolate large quantities of PMNs from horse peripheral blood. This involved creating a ‘clean’ sample solely of PMNs, which was necessary for the subsequent tests.
• Three different tests were conducted to evaluate the function of these equine PMNs – the ingestion of Staphylococcus aureus, nitroblue tetrazolium reduction, and iodination.
• Four variations of R. equi – live bacteria, heat-killed bacteria, a pellet from heat-killed bacteria, and a supernatant fluid from heat-killed bacteria – were added individually to the PMNs in each test.

Results and Findings

• No R. equi preparations had any noticeable impact on S. aureus ingestion by the equine PMNs. This implies that the presence of R. equi does not affect the capacity of horse PMNs to ingest this particular bacteria.
• The nitroblue tetrazolium reduction in PMNs, which is a measure of oxidative metabolism, was decreased when both the pellet and the supernatant fluid from heat-killed R. equi were added. This indicates that these forms of R. equi can suppress oxidative metabolism in PMNs.
• All variations of R. equi depressed values for the iodination reaction. This signifies that R. equi reduces the activity of the myeloperoxidase-H2O2-halide system of the PMN, a process important for the PMN’s antibacterial response.
• Further tests on the supernatant fluid from heat-killed R. equi showed that it retained the ability to inhibit iodination after being autoclaved and/or passed through a 10,000 MW filter. This finding indicates that this inhibitory effect is caused by a stable component in the supernatant fluid.

Conclusion and Implications

• The findings of the study suggest that R. equi can interfere with the bactericidal mechanisms of equine PMNs, specifically via suppressing oxidative metabolism and reducing the activity of the myeloperoxidase-H2O2-halide system.
• This suggests that R. equi has a surface component that allows it to hamstring the antibacterial capacity of PMNs, which could be an important factor in its ability to survive within a host body.
• This information further our understanding of how R. equi operates within a host, which could aid in the development of treatments or prevention methods for infections caused by the bacterium.