Differential effects of copper and zinc on human peripheral blood monocyte cytokine secretion

Abstract

The addition of copper and zinc salts to human peripheral blood leukocytes cultured in complete medium containing endotoxin and fetal calf serum stimulated tumor necrosis factor (TNF) secretion in a concentration-dependent manner. The secretion of interleukin-1 beta (IL-1 beta) and interleukin-6 (IL-6) was inhibited by copper under the same culture conditions, while zinc stimulated IL-1 beta secretion in a concentration-dependent manner and had no effect on leukocyte IL-6 release. Both copper and zinc induced increases in TNF mRNA (54 and 14%, respectively) when compared to cells cultured in complete medium alone. In serum-free, low endotoxin medium (less than 6 pg/ml), both copper and zinc failed to stimulate either TNF or IL-1 beta secretion. Under the same conditions the addition of lipopolysaccharide (LPS), at concentrations above 0.01 micrograms/ml, induced a concentration-dependent release of both cytokines. When either copper or zinc were combined with 0.01 micrograms/ml LPS, a synergistic stimulation of TNF secretion resulted. IL-1 beta secretion, unlike TNF, was not synergistically stimulated by combining metals and LPS in serum-free medium. Combining copper and zinc with inhibitors of TNF secretion, transforming growth factor beta, prostaglandin E2, and plasma alpha-globulins, resulted in a reduction of the suppressive effects of each of these agents. This study suggests that the trace metals copper and zinc may play important and possibly distinct roles in regulating leukocyte secretion of TNF, IL-1 beta, and IL-6.