ABSTRACT
We have previously shown that IFN-beta, a key cytokine associated with the early phase of the innate host defense, can prevent the generation of human Th1 cells. Specifically, we demonstrated that IFN-beta prevents the in vitro monocyte-derived mature dendritic cell (DC)-dependent differentiation of naive Th cells into IFN-gamma-secreting Th cells, as a result of its ability to inhibit DC IL-12 secretion. The goal of the present study was to identify how IFN-beta negatively regulates IL-12 secretion by DC. We report that in our Th cell differentiation model, DC IL-12 secretion is dependent on the CD40L/CD40 accessory pathway, and, utilizing a Th cell-free system, we find that IFN-beta inhibits anti-CD40 mAb-induced DC secretion of the p40 chain of the IL-12 heterodimer. In addition, we show that IFN-beta-mediated inhibition of CD40 signaling does not interfere with all signaling pathways emanating from CD40, since anti-CD40 mAb-induced DC IL-6 secretion is augmented by IFN-beta. Thus, our results demonstrate that signaling from CD40 is differentially regulated by IFN-beta. A second critical element of innate immunity involves the response against components of bacterial membranes such as LPS. DC respond to LPS by secreting IL-6 and IL-12. In contrast to CD40-dependent IL-6 and IL-12 secretion, we find that LPS-induced DC secretion of p40 IL-12 and IL-6 is not affected by IFN-beta. Our findings show that IFN-beta influences the generation of acquired immune responses through its regulation of CD40-dependent DC functions.
