Effects of stallion seminal plasma on hydrogen peroxide release by leukocytes exposed to spermatozoa and bacteria

The ability of stallion seminal plasma to modify phagocytosis of spermatozoa and Streptococcus zooepidemicus was examined. Phagocytosis was monitored indirectly as the H2O2 produced by peripheral blood leukocytes after addition of spermatozoa or bacteria. Hydrogen peroxide production after addition of ejaculated spermatozoa was greater (P less than 0.01) than after addition of epididymal sperm. Furthermore, pre-incubation of epididymal sperm with 6.25-50% seminal plasma caused a dose-dependent increase in subsequent H2O2 production by leukocytes (P less than 0.05). In addition, equine serum was capable of opsonizing epididymal and ejaculated sperm. Seminal plasma also directly stimulated phagocyte function because leukocytes preincubated with 12.5% or 25% seminal plasma released more H2O2 after addition of S. zooepidemicus than control leukocytes (P less than 0.05). It is suggested that the opsonization of spermatozoa and the direct stimulation of phagocytes by seminal plasma may represent mechanisms for clearing spermatozoa and bacteria from the reproduction tract.