Negative feedback regulation of T helper type 1 (Th1)/Th2 cytokine balance via dendritic cell and natural killer T cell interactions.

The ability of extracellular stimuli to modulate dendritic cell (DC) activation of natural killer T (NKT) cells was not well understood. We investigated the effects of the T helper type 1 (Th1)/Th2-cytokine environment on DC induction of NKT cell-mediated cytokine production in mice. Pretreatment of myeloid DCs with Th1 or Th2 cytokines, interleukin (IL)-4 or interferon (IFN)-gamma, led to the enhanced production of reciprocal cytokines by NKT cells (eg, IL-4 pretreatment led to the enhanced production of Th1 cytokines) in vitro and in vivo. Thus, the recognition of Th1 or Th2 cytokines by DCs acts as a negative feedback loop to maintain Th1/Th2-cytokine balance via NKT cell functions. Using these data, we manipulated cytokine levels and innate cytolytic activity in vivo to increase an antitumor response. This is the first description of a novel regulation system governing Th1/Th2 cytokine balance involving DCs and NKT cells.