Effects of zinc on the reactive oxygen species generating capacity of human neutrophils and on the serum opsonic activity in vitro

To investigate the effects of zinc on non-specific immune functions, we used the chemiluminescence method to examine the capacity of human neutrophils to produce reactive oxygen species and accompanying serum opsonic activity. When neutrophils were stimulated with both opsonized zymosan and phorbol myristate acetate in the presence of 1-10^-3 mmol/L zinc lucigenin-dependent CL responses were stable or declined, whereas luminol-dependent CL responses were significantly enhanced. The results suggest that zinc activates protein kinase C and promotes MPO degranulation and ROS metabolism, especially in hypochlorous acid production, which have the direct action of causing microbial death. Further, the lucigen-dependent CL response stimulated with OZ was strongly enhanced by anti-MPO antibodies, whereas the enhancement was less in the presence of zinc, suggesting that zinc may suppress the receptor-mediated signal transduction process. Both responses were inhibited at 10 mmol/L. Serum opsonic activity was enhanced by zinc at 10^-4 and 10^-3 mmol/L but reduced at 10 mmol/L. These data indicate that addition of zinc around and above normal physiological concentrations facilitates neutrophil functional activity and serum opsonic activity, whereas these are inhibited by a lack of zinc or an excessive amount, suggesting that zinc is essential for optimal functioning of non-specific immunity.