Influence of age and plasma treatment on neutrophil phagocytosis and CD18 expression in foals.

The research examines how age and plasma treatment affect the ability of neutrophils (a type of white blood cell) to consume harmful bacteria (phagocytosis), the expression of the CD18 receptor, and the capacity for serum to enhance immune response (opsonic capacity) in young horses (foals). The findings suggest that young foals have a temporary deficiency in serum opsonic capacity which negatively impacts their neutrophil phagocytosis, potentially increasing their susceptibility to infections.

Research Design and Method

• The study collected blood samples from 13 foals at seven different time points between the ages of 2 and 56 days, as well as from 16 adult horses for comparison.
• Of these 13 foals, six were treated with adult plasma when they were only a week old.
• The research involved analyzing neutrophil phagocytosis of yeast after various opsonizations (enhancement of immune response) and examining the expression of the CD18 receptor via flow cytometry, a technique used to measure the physical and chemical characteristics of cells or particles.

Findings

• Autologous serum opsonization resulted in 52 ± 6.1% phagocytic neutrophils in 2-day-old foals, a significantly lower rate than in adult horses, which stood at an average of 84 ± 3.1%.
• Neutrophils in foals also ingested less yeast than those in adults.
• Opsonic capacity (the ability of blood serum to enhance phagocytosis) increased with age, reaching similar levels to adult horses at 3-4 weeks of age.
• Plasma treatment was found to increase serum opsonic capacity.
• When pooled adult horse serum or anti-yeast IgG was used as opsonin, the phagocytic capacity of foal neutrophils was equal to or higher than those in adults.
• There was a negative correlation between serum IgG concentration and serum opsonic capacity in foals.
• CD18 receptor expression was higher in neutrophils from foals (younger than 21 days old) than those from adult horses.

Conclusions

• Overall, the study revealed that foals are temporarily deficient in serum opsonic capacity which negatively impacts their neutrophil phagocytosis capacity.
• Changes in serum opsonins, which are not related to IgG, may be significant factors in susceptibility to infections in foals.