Inhibitor κB and nuclear factor κB in granulocyte-macrophage colony-stimulating factor antagonism of dexamethasone suppression of the macrophage response to Aspergillus fumigatus conidia

Abstract

Background. The dexamethasone (DEX) immunosuppressive effect on macrophage killing activity and cytokine production in response to Aspergillus fumigatus conidia is antagonized by granulocyte-macrophage colony-stimulating factor (GM-CSF). The molecular mechanism is unknown. We postulated that this antagonism is mediated by inhibitor κB (IκB) induction by DEX and is opposed by acceleration of IκB degradation by GM-CSF with or without conidia stimulation, with corresponding effects on translocation and activation of nuclear factor κB (NF-κB). Methods. We studied 2 types of cells, resident peritoneal macrophages from CD-1 mice and the murine macrophage RAW264.7 cell line. Cells were unstimulated or stimulated with conidia and simultaneously treated with DEX, GM-CSF, or DEX plus GM-CSF, for 2-4 hours. IκB degradation and NF-κB activation were assessed by Western blot. Results. Macrophages stimulated with conidia alone increased NF-κB translocation. DEX increased IκB levels in cytoplasm and blocked translocation of NF-κB to the nucleus in unstimulated and conidia-stimulated macrophages. Conversely, GM-CSF decreased IκB levels. GM-CSF reversed the effect of DEX on IκB levels. NF-κB levels were minimal in DEX-treated macrophage nuclear extracts, compared with those from GM-CSF-treated and GM-CSF plus DEX-treated macrophages. Conclusion. GM-CSF can reverse the DEX immunosuppressive effect by enhancing IκB degradation and promoting NF-κB translocation. This would allow macrophage production of proinflammatory cytokines, facilitating resistance to aspergillosis. © 2006 by the Infectious Diseases Society of America. All rights reserved.