Copper Deficiency Suppresses Effector Activities of Differentiated U937 Cells

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Abstract
Dietary copper (Cu) deficiency impairs both innate and acquired branches of immunity. Specific roles of Cu in the activation and effector activities of host-defense cells remain largely unknown. The effects of Cu status on effector activities of a monocytic cell line were investigated as an initial step in the elucidation of specific functions of Cu in phagocytic cells. Exposure of differentiating U937 human promonocytic cells to 5 μmol/L 2,3,2-tetraamine (tet), a high affinity Cu chelator, for 4 d decreased cellular Cu by 62% without altering cellular Cu,Zn-superoxide dismutase (SOD) activity, Zn content, mitochondrial activity and protein synthesis. In contrast, Cu deficiency suppressed the respiratory burst activity and markedly compromised the ability of U937 cells to kill Salmonella. Similarly, treatment of RAW264.7 murine macrophages with 5 μmol/L tet decreased cell Cu by 78% and Cu,Zn-SOD activity by 15% and increased bacterial survival by 180%. The tet-induced impairment of respiratory burst and bactericidal activities was blocked in cultures supplemented with Cu, but not Zn or Fe. In addition, lipopolysaccharide (LPS)-induced secretion of the inflammatory mediators, tumor necrosis factor-α, interleukin (IL)-1β, IL-6 and prostaglandin E2 (PGE2), was decreased by 30–60% in tet-treated U937 cells. Flow cytometric analysis of the surface antigens CD11b and CD71 showed that the suppressed activities of Cu-deficient cells were not due to an attenuation in the degree of differentiation or secondary iron deficiency. These data demonstrate that U937 cells provide a useful model for examining the biochemical roles of Cu in monocyte activity.