Rhodococcus (Corynebacterium) equi: bactericidal capacity of neutrophils from neonatal and adult horses.

The research examined how well neutrophilic leukocytes in horses are able to kill the bacteria Rhodococcus equi, and if age has a significant effect on this ability. The study found that although most horses of all ages showed similar killing ability, some newborn foals demonstrated a significantly weaker ability, potentially increasing their vulnerability to R equi infections.

Study Objectives and Methodology

• The researchers aimed to compare the ability of polymorphonuclear neutrophilic leukocytes (PMNL), a type of white blood cell, to kill the bacteria Rhodococcus equi in horses across different ages.
• They used a radioisotope bactericidal assay to measure the killing capacity of PMNL in three groups of horses: Very young foals (around 3 days old), slightly older foals (roughly 36 days old), and adult horses.
• Bacteria for the experiment were sourced from the lungs of a foal suffering from R equi pneumonia. To stimulate the immune response, the bacteria were coated with a specific antibody found in mature horse serum.

Results

• The study found the average percentage of R equi killed by PMNL was similar across all three groups: 78.9% for the youngest foals, 90.1% for the older foals, and 87.9% for adult horses.
• However, two of the foals in the youngest group (15% of this group), showed a significantly weaker response, killing only around 30.5% of the bacteria. This figure was much lower than the averages for the other foals in the same age group.

Implications

• The results indicate that, in general, the neutrophilic leukocytes of newborn, young, and adult horses have a similar capability to kill R equi bacteria.
• However, the reduced killing capacity observed in some newborn foals may signal an increased vulnerability to R equi infections. This could potentially mean that these particular foals have a weaker immune response, which makes them more susceptible to disease, making this an important factor to consider in terms of clinical and veterinary care.