Endogenous interleukin 6 plays an obligatory role in interleukin 4‐dependent human IgE synthesis

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Abstract
The lymphokine interleukin (IL) 4 plays a crucial role in the regulation of IgE synthesis. In the present study, the cellular and cytokine requirements for the IL 4-dependent induction of IgE synthesis in humans were analyzed. Recombinant IL4 could induce IgE synthesis by peripheral blood mononuclear cells and autologous T/B cell mixtures, but not by highly purified B cells. IgE induction by IL4 was strongly decreased in monocyte-depleted peripheral blood mononuclear cells. These results show that the induction of IgE synthesis by recombinant IL 4 is T cell dependent and optimal in the presence of monocytes. IL5 and IL6, but not IL2, IL1 and tumor necrosis factor-α, strongly up-regulated the IL4-dependent synthesis of IgE, with modest effects on cell proliferation. An anti-IL6 polyclonal antibody strongly inhibited IL4-driven IgE production. Endogenous IL6 plays, therefore, an obligatory role in the IL4-dependent induction of IgE. However, a combination of IL 4, IL 5 and IL 6 (with or without IL 1) at optimal concentrations could not induce IgE synthesis by purified normal B cells, indicating that cytokine-mediated signals, although essential, are not sufficient for the IL 4-dependent induction of IgE synthesis.