Neutrophil function in healthy aged horses and horses with pituitary dysfunction.

The research is focused on understanding how equine pituitary pars intermedia dysfunction (PPID), a hormonal disease in horses, affects their immune system. The study analyzed how neutrophils, a type of immune cell, function in both healthy old horses and horses affected by PPID.

Understanding the Issue

• Equine pituitary pars intermedia dysfunction (PPID) is known to cause immunosuppression in horses, leaving them susceptible to bacterial infections.
• While it’s known that PPID negatively impacts the immune system, the mechanisms behind this immune dysfunction haven’t been fully elucidated.
• Neutrophil is a type of white blood cell instrumental in the immune response, and its dysfunction might contribute to immunosuppression.
• Hormones such as α-melanocyte stimulating hormone (α-MSH) and insulin, which are present at high concentrations in horses with PPID, can influence the immune function.
• In other species like rodents and humans, α-MSH and related hormones have been observed to impair neutrophil function. They reduce the production of superoxide (a reactive oxygen species crucial in immune response), neutrophil migration and adhesion which are all vital to achieving an immune response.

Study Objectives and Approach

• The primary aim of the study was to evaluate if PPID causes impairment in neutrophil function in horses, and if it does, whether there exists a correlation between plasma α-MSH or insulin concentration and the severity of neutrophil dysfunction.
• Specifically, the researchers assessed neutrophil phagocytosis, oxidative burst activity, chemotaxis (attraction or repulsion of cells based on chemical gradients) and adhesion (stickiness or ability of cells to attach to each other).

Key Findings

• The study observed that horses with PPID had reduced neutrophil function, with notable decreases in oxidative burst activity and adhesion.
• Chemotaxis was found to be higher in healthy aged horses as compared to both young and aged horses with PPID.
• Rather than individual hormone concentration, the ratio of insulin to α-MSH was correlated with neutrophil oxidative burst activity. This suggests that both hormones might play a role in mediating the immune effects.
• The impaired neutrophil function in horses with PPID due to altered hormone concentrations may be a factor contributing to the increased risk of opportunistic infections.

Future Directions

• It needs to be determined whether regulating hormone concentration profiles in horses with PPID through therapeutic intervention can improve neutrophil function and reduce infections.