Effect of blood serum, caffeine and heparin on in vitro phagocytosis of frozen-thawed bull sperm by neutrophils derived from the peripheral blood of cows

Although polymorphonuclear leukocytes (PMNs) are recruited into the uterine lumen to phagocytize sperm, factors controlling the phagocytotic ability of PMNs in cattle are not well documented. The objective was to determine the effects of blood serum, caffeine, and heparin on chemotaxis of PMNs for sperm and phagocytosis of sperm by PMNs in cows. Polymorphonuclear leukocytes were obtained (centrifugation) from a cow's peripheral blood. In Experiment 1, the chemotactic activity of PMNs increased (P < 0.01) when fresh serum was included in the medium (1226 cells/mm² in serum vs. 1110 cells/mm² in BSA), regardless of the presence of sperm, whereas heat-inactivated serum (1099 cells/mm²) did not affect their activity (P = 0.65). Phagocytosis of live and dead sperm by PMNs both increased (P < 0.01) in the presence of fresh serum (incidences of 54.5 and 48.0%, respectively), but stimulation was decreased (P < 0.01) by supplementation of the medium with ≥1 mM caffeine (20.6-30.3%). Serum-stimulated chemotactic activity of PMNs (1218 cells/mm²) was also decreased (P < 0.01) in the presence of caffeine (1090 cells/mm²). Furthermore, supplementation of PMNs with heparin in the presence of serum decreased (P < 0.01) both phagocytotic (from 43.8% to 21.5-31.7%) and chemotactic activities of PMNs (from 1124 to 1048-1108 cells/mm²). We inferred that opsonization in the presence of active complement stimulated phagocytotic and chemotactic activities of PMNs, and that both caffeine and heparin decreased serum-stimulated phagocytotic and chemotactic activities of PMNs.