Stress-associated Regulation of TNF-a in Innate Immunity

Objective: Decreased immune resistance to infection such as periodontal diseases and recurrent herpes simplex virus has been associated with catecholamine-mediated stress responses. The inflammatory cytokine TNF-a mediates both local and long-range host defense mechanisms including apoptosis. Previous studies in this laboratory have revealed that in lymphocytes TNF-a protein and mRNA are down-modulated by catecholamines through a b-adrenergic dependent, cAMP-dependent mechanism. In this study we extend these investigations to analysis of the effects of norepinephrine (NE) and cAMP on TNF-a dynamics in RAW 264.7 macrophages, a model for the innate arm of the immune response. Methods: RAW 267.4 cells (1x10⁷ cells) cultured at 37°/5% CO₂ in serum-free Iscove's MDM containing 1µg/ml LPS were treated with 100µM NE, 100µM isoproterenol (ISO) and 500µM DBcAMP. TNF-a protein was assayed by ELISA and TNF-a mRNA was determined by RNase protection assay. Results: Incubation of RAW cells with NE, ISO or DBcAMP resulted in a time-dependent decrease in the level of TNF-a protein assayed by ELISA. After 6 hr treatment with NE, or ISO, cellular TNF-a protein decreased to levels 65-70% lower than control cells. Incubation of cells with 500µM DBcAMP resulted in a 90% decrease of TNF-a. The decrease in TNF-a protein mediated by NE in these cells was completely reversed by the b-adrenergic antagonist, propranolol (10µM) revealing a b-adrenergic mediated mechanism. Both NE and cAMP down-regulated TNF-a mRNA and preliminary experiments suggest that this involves altered TNF-a mRNA stability. Conclusion: These investigations argue that stress mediated through NE may impair innate immunity and apoptosis in macrophages by down-regulation of TNF-a through a b-adrenergic/cAMP-dependent mechanism in parallel with NE control of TNF-a in lymphocytes. Supported by DE13684