Treatment of Neonatal Foals with Immunostimulants Enhances Phagocytic Cell Activity Against Ex Vivo Infection with Rhodococcus equi
ACVIM 2008
C. Ryan; S. Giguère.
University of Florida, College of Veterinary Medicine
Gainesville, FL, USA

The objective of this study was to determine the effect of immunostimulants on neutrophil and macrophage activity against ex vivo infection with R. equi. Seventeen neonatal foals were treated with Zylexis®, EqStim®, or saline on days 7, 9, and 15 of life. Peripheral blood mononuclear cells and BAL cells were collected on day 7 (pre-treatment), 19, 31, and 43. Neutrophil phagocytosis and oxidative burst in response to R. equi infection was assessed using a flow cytometric assay. Intracellular proliferation of R. equi within macrophages was assessed by light microscopy for samples collected on days 7 and 19.

Neutrophils from foals treated with Zylexis® had a significantly greater ability to phagocytize opsonized R. equi and had higher oxidative burst on day 19 and day 31 (post-treatment) compared to baseline values (P < 0.05). On day 31, foals treated with Zylexis® had significantly greater phagocytosis and oxidative burst than foals treated with EqStim® (P < 0.05). The effect of Zylexis on neutrophil function was no longer detectable on day 43. There was no significant effect of time on phagocytosis and oxidative burst in control foals and in foals pretreated with EqStim. Treatment with EqStim® resulted in significantly less intracellular proliferation of R. equi within monocyte-derived and BAL macrophages on day 19 compared to control foals (P <0.05) but not compared to foals treated with Zylexis®.

In conclusion, treatment of neonatal foals with Zylexis® enhances the activity of neutrophils whereas EqStim® enhances activity of macrophages following ex vivo infection with R. equi.

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Clare Ryan

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