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Interleukin-1 (IL-1) treatment of human WI-38 lung fibroblasts results in granulocyte-macrophage colony-stimulating factor (GM-CSF) expression as well as a delayed increase in prostaglandin E2 (PGE2) production that closely correlates with the decline of GM-CSF mRNA levels. Pretreatment with PGE2 reduces the IL-1 induced GM-CSF mRNA and protein expression to 10% to 15% of control values at concentrations of PGE2 that are endogenously produced after IL-1 stimulation. Inhibition of PGE2 synthesis by indomethacin prolongs the IL-1 induced GM-CSF mRNA expression and increases the cumulative GM-CSF protein secretion. Exposure of WI-38 fibroblasts to PGE2 results in an increase in intracellular cyclic adenosine monophosphate (cAMP) levels. The inhibition of GM-CSF expression by PGE2 can be mimicked by stable cAMP analogs as well as cAMP elevating agents such as cholera toxin, forskolin, and isobutylmethylxanthine. Thus the inhibition exerted by PGE2 is mediated via cAMP. Taken together, these results suggest that IL-1 stimulation of human fibroblasts provides not only the upregulatory signal for GM-CSF expression but also a delayed and indirect downregulatory signal that serves to limit GM-CSF expression in the continued presence of IL-1.

Diethyldithiocarbamate (DDTC) is a biochemical modulating agent that protects murine bone marrow progenitor cells from the cytotoxicity of a variety of cancer chemotherapeutic agents. However, the mechanism of this protection is not well understood. Long-term human bone marrow cultures (LTBMC) were established and at day 17 treated with 30 mumol/L DDTC for 1 hour, after which DDTC was removed and replaced with complete medium. Conditioned medium was then collected 6, 12, 24, and 48 hours later and analyzed for the presence of cytokines. A time- dependent increase in granulocyte-macrophage colony-stimulating factor (GM-CSF) (12-fold), granulocyte-CSF (G-CSF) (66-fold), interleukin (IL)- 6, (three-fold), IL-1 beta (161-fold), and tumor necrosis factor (TNF)- alpha (25-fold) was observed. The maximum increase for the factors other than TNF-alpha was at 24 to 48 hours posttreatment. However, TNF- alpha peaked as early as 6 hours post-DDTC. When conditioned medium from these cultures was tested in a granulocyte-macrophage progenitor cell (GM-CFC) assay, an increase in colony formation was observed that correlated with the increased levels of cytokines in the medium. The specificity of this effect was confirmed by the fact that the closely related congener bis(hydroxyethyl)dithiocarbamate was devoid of colony- stimulating activity. The addition of antibodies for TNF-alpha and/or IL-1 alpha following DDTC treatment did not inhibit the release of GM- CSF, G-CSF, or IL-6 from the LTBMC. These results suggest that DDTC accelerates bone marrow recovery following myelotoxic drug treatment via increased production of cytokines that are known to be essential for hematopoiesis.