Tumor Necrosis Factor α Decreases, and Interleukin-10 Increases, the Sensitivity of Human Monocytes to Dexamethasone: Potential Regulation of the Glucocorticoid Receptor

Resistance to glucocorticoid therapy has been observed in patients with autoimmune/inflammatory diseases and may be related to the inflammatory process itself. The aim of this study was to examine the ability of tumor necrosis factor α (TNFα, a proinflammatory cytokine) and interleukin (IL)-10 (an anti-inflammatory cytokine) to differentially regulate the sensitivity of human monocytes/macrophages to glucocorticoids. To accomplish this, we first analyzed the pattern of TNFα and IL-10 inhibition by dexamethasone in LPS-stimulated whole-blood cell cultures. Second, we studied the modulation of the sensitivity of these cells to dexamethasone by preincubation with TNFα or IL-10 and measurement of LPS-stimulated IL-6 secretion. In addition, we evaluated the effect of dexamethasone on phorbol-myristate-acetate-stimulated IL-1 receptor antagonist secretion by the human monocytic cell line U937. Finally, we investigated whether the modulation of corticosensitivity in TNFα- and IL-10-pretreated U937 cells was related to a change of the glucocorticoid receptor concentration and affinity. Dexamethasone had different effects on LPS-induced TNFα and IL-10 secretion; whereas it suppressed TNFα in a dose-dependent fashion, its effect on IL-10 secretion was biphasic, producing stimulation at lower, and inhibition at higher doses. The concentration of LPS employed influenced the effect of dexamethasone on IL-10 secretion (P < 0.001). Pretreatment with TNFα diminished, and with IL-10 improved, the ability of dexamethasone to suppress IL-6 secretion in whole-blood cell cultures (P < 0.01 for both) and to enhance IL-1 receptor antagonist secretion by U937 cells (P < 0.05 for both). TNFα decreased (P < 0.001), while IL-10 increased (P < 0.001), the concentration of dexamethasone binding sites in these cells, with no discernible effect on their binding affinity. We conclude that glucocorticoids differentially modulate TNFα and IL-10 secretion by human monocytes in a LPS dose-dependent fashion and that the sensitivity of these cells to glucocorticoids is altered by TNFα or IL-10 pretreatment; TNFα blocks their effects, whereas IL-10 acts synergistically with glucocorticoids. This is accompanied by opposite glucocorticoid receptor changes, respectively opposing and favoring glucocorticoid actions. This study suggests that the pattern of pro-/antiinflammatory cytokine secretion may alter the response of patients to glucocorticoid therapy.