The effect of bovine seminal plasma on the function and integrity of bovine neutrophils

Spermatozoa, by virtue of their high content of polyunsaturated fatty acids and limited antioxidant activity, are highly sensitive to lipid peroxidation. Sources of reactive oxygen species in the female genital tract include neutrophils recruited in response to insemination or those contained within the ejaculate, or even spermatozoa themselves. This study was undertaken to investigate the effect of seminal plasma of bulls on bovine neutrophils. Seminal plasma was removed from ejaculates of 6 healthy bulls by centrifugation. Neutrophils were isolated from jugular venous blood samples obtained from lactating Holstein cows. Seminal plasma was found to decrease measured superoxide anion production by activated neutrophils (P=0.008) in a concentration-dependent manner over the range tested (0 to 16%). This effect may reflect superoxide scavenging by the seminal plasma or direct inhibition of the neutrophils. It has the potential physiological advantage of protecting spermatozoa from oxidative damage. Seminal plasma was found to reduce homotypic neutrophil aggregation dramatically (P<0.0001). At a seminal plasma concentration of 0.2% neutrophil aggregation was virtually abolished. Homotypic neutrophil aggregation depends on the CD11b/CD18 (Mac-1) receptor, which also functions as the C3bi receptor (known as complement receptor-3 or CR3). If this receptor is down-regulated, the ability of neutrophils to phagocytose complement-opsonized microorganisms would be compromised. Finally, seminal plasma was found to increase neutrophil permeability to trypan blue in a concentration and time dependent fashion (P<0.0001), indicating a direct cytotoxic effect. Taken together, these findings indicate a profound inhibition of neutrophil function by bovine seminal plasma. While these mechanisms are likely to protect spermatozoa from oxidative damage or phagocytosis, they also have the potential to diminish defense against pathogenic microorganisms.