Rhodococcus equi: equine neutrophil chemiluminescent and bactericidal responses to opsonizing antibody.

The research article explores how equine neutrophils respond to the presence of R. equi-specific antibodies using assays for chemiluminescence and bactericidal activity. It notes a significantly higher response when these neutrophils are exposed to serum from foals with R. equi infections compared to control serum.

Research Methods

• The serum’s capacity to opsonize, or mark foreign cells for destruction, was tested using antibody-specific and antibody-deficient sera.
• These serum types were then subjected to luminol-dependent chemiluminescence (LDCL) and bactericidal assays, both geared at investigating the biological response of peripheral blood polymorphonuclear neutrophilic leukocytes (PMNLs) when exposed to R. equi opsonized with different types of serum.
• These bacteria were harvested from the lungs of a foal with R. equi pneumonia, and neutrophils for each type of assays were obtained from two different adult horses.
• All sera samples were first complement-inactivated at 56 degrees C for half an hour before being used in the assays.
• The bactericidal assays used radioisotopes to measure the destructive capacity of the PMNLs against R. equi, and the LDCL assay used scintillation counting to measure the PMNLs’ chemiluminescent response to the R. equi.

Research Findings

• The LDCL was significantly higher with the principal sera (from foals with infections) than with the control serum, with a mean peak reading of 2.4 X 10(5) cpm vs. 0.018 X 10(5) cpm in the control group.
• Similarly, the bactericidal capability of PMNLs against R. equi was significantly enhanced in the principal sera, with a mean peak of 95.2% kill vs. 54.6% in the control group.
• Furthermore, ELISA values for R. equi-specific antibody were also significantly higher in the principal sera than in the controls, proving the presence and effectiveness of opsonization activity in complement-inactivated sera of foals with R. equi infections.

Conclusion

• This study provides important insights into how equine neutrophils respond to R. equi-specific antibodies, showing a higher rate of bactericidal activity and chemiluminescent response in sera from foals with active R. equi infections. Science has yet to fully elucidate the exact mechanisms at play, but this study suggests an important role for opsonic activity in the horse immune response to R. equi.
• The results of this study are crucial in furthering the understanding of how pathogens are targeted and destroyed by the horse immune system, and can have future applications in diagnosing and treating horses with bacterial infections.