Regulation of immune function in neonatal foals: Responses to vaccination and administration of immunostimulants.

摘要

Foals are thought to be susceptible to certain infectious diseases because their immune system is naive or not as competent as that of adult horses. However, the differences in host defense mechanisms between newborn foals, older foals, and adult horses are poorly understood. The objectives of the first part of this study was to compare the frequency of IFN-gamma and IL-4 secreting cells of newborn foals to that of older foals and adult horses, and to determine the effect of the type of mitogen used for in vitro stimulation on the relative frequency of cells secreting these cytokines. The frequency of IFN-gamma and IL-4 secreting cells was significantly lower in both groups of foals compared to adult horses. Regardless of age, the type of mitogen used for in vitro stimulation had a significant effect on the IFN-gamma/IL-4 ratio. The objective of the second part of this study was to determine the effect of comercially available immunostimulants on neutrophil, macrophage, and lymphocyte function following ex vivo exposure to Rhodococcus equi. Inactivated Propionibacterium acnes (PA), inactivated parapoxvirus ovis (PPVO), or saline (control) was administered to foals on days 0 (7 days of age), 2, and 8. Treatment with PPVO significantly increased phagocytosis of R. equi and oxidative burst activity of neutrophils whereas treatment with PA decreased intracellular proliferation of R. equi within monocyte-derived macrophages, The objective of the third part of this study was to compare serum immunoglobulin concentrations, antigen-specific lymphoproliferative responses, and cytokine profile of proliferating lymphocytes of 3-day old foals, 3-month old foals, and adult horses following vaccination with a killed adjuvanted vaccine. Both humoral and cell-mediated immune responses to the vaccine were modest in 3-day old foals. Although immune responses improved with age, 3-month old foals did not respond with the same magnitude as adult horses. Newborn foals did not have a bias toward a Th2 response following vaccination with the killed vaccine used.