Regulation of Fc-induced IL-6 from human peripheral blood mononuclear cells

Previous experiments demonstrated that aggregated immunoglobulin and the Fc fragment of human IgG can induce interleukin-6 (IL-6) secretion from peripheral blood monocytes. The data herein indicate that Fc-induced IL-6 is modulated by IL-1, IL-4 and interferon (IFN-gamma). When added with Fc fragments, IL-1 and IFN-gamma increased IL-6 production. IL-4 added with Fc fragment did not influence IL-6 production although IL-4 added with LPS was inhibitory to IL-6 production. However, when PBMC were pre-treated with IL-4, IL-4 downregulated Fc-induced IL-6 secretion. The inhibitory effect of IL-4 in the pre-treatment phase could be overcome with a high concentration of IFN-gamma added with the IL-4. Both IL-4 and IFN-gamma acted in a dose- and time-dependent manner. By dot blot analysis, IL-6 mRNA production appeared to be decreased in amount and duration by IL-4 whereas IFN-gamma increased the amount of IL-6 mRNA production. Hence, IL-4 and IFN-gamma appear to have opposing effects and may play a balancing role in the regulation of IL-6 production secondary to Fc exposure.