Serum opsonization capacity, phagocytosis, and oxidative burst activity in neonatal foals in the intensive care unit.

Background: Phagocytic activity of neonatal foals has been reported to be similar to that of adult horses, but serum opsonization capacity develops with age and may be further altered when opsonins are consumed during infection.

Hypothesis: Phagocytosis, oxidative burst activity, and serum opsonization capacity in neonatal foals admitted to an intensive care unit are reduced in comparison with control foals.

Animals: Blood samples were collected from hospitalized neonatal foals and from control foals. Hospitalized foals were characterized as sick or septic on the basis of a sepsis score and received intravenous plasma transfusion.

Methods: Phagocytosis, oxidative burst activity, and serum opsonization capacity were tested with flow cytometric analysis. Serum immunoglobulin and complement component 3 concentrations were determined with radial immunodiffusion. Serum amyloid A concentration was assayed with a commercially available solid-phase Sandwich ELISA Kit. Data were analyzed with nonparametric and regression methods. Alpha was set at P = .05.

Results: Phagocytic functions of septic and sick foals were lower than control foals in the initial phase of the study (P = .01). Opsonization capacity was significantly higher when bacteria were opsonized with serum from septic (P = .029) and sick (P = .006) foals than from control foals on day 1. Opsonization capacity in septic foals was comparable with control foals on days 2 and 5. This effect was not accompanied by an increase in serum complement C3 or immunoglobulin G concentrations independently.

Conclusions And Clinical Importance: Our results suggest that phagocytic function could be decreased in hospitalized foals. The synergistic effect of opsonic elements provided by plasma transfusion may sustain opsonization capacity during sepsis.